Endophytes and related methods
The present invention relates to a method for identifying and/or characterising an endophyte strain, said method including providing a plurality of samples of endophytes, subjecting said endophytes to genetic analysis, subjecting said endophytes to metabolic analysis and selecting endophytes having a desired genetic and metabolic profile. The present invention also relates to novel endophytes having a desired toxin profile wherein the endophyte produces significantly less toxic alkaloids compared with a control endophyte such as standard toxic (ST) endophyte; and/or significantly more alkaloids conferring beneficial properties compared with a control endophyte such as ST endophyte. The present invention also relates to endophyte variants having a desired genetic and metabolic profile, wherein said endophyte variants possess genetic and/or metabolic characteristics that result in a beneficial phenotype in a plant harbouring or otherwise associated with the endophyte variant. Preferably said endophyte variants are generated by polyploidisation or induced chromosome doubling.
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This application is a continuation in part of PCT/AU2011/000020, filed Jan. 7, 2011, which claims priority from Australian Patent Application 2010900054 filed Jan. 7, 2010, and Australian Patent Application 2010902821, filed Jun. 25, 2010, and also claims priority from Australian Patent Application Nos. 2012902275 and 2012902276, filed Jun. 1, 2012. All of these applications are incorporated herein by reference in their entirety.
FIELD OF THE INVENTIONThe present invention relates to endophytic fungi (endophytes), including modified variants thereof, and to nucleic acids thereof. The present invention also relates to plants infected with endophytes and to related methods, including methods of selecting, breeding, characterising and/or modifying endophytes.
BACKGROUND OF THE INVENTIONImportant forage grasses perennial ryegrass and tall fescue are commonly found in association with fungal endophytes.
Both beneficial and detrimental agronomic properties result from the association, including improved tolerance to water and nutrient stress and resistance to insect pests.
Insect resistance is provided by specific metabolites produced by the endophyte, in particular loline alkaloids and peramine. Other metabolites produced by the endophyte, lolitrems and ergot alkaloids, are toxic to grazing animals and reduce herbivore feeding.
Considerable variation is known to exist in the metabolite profile of endophytes. Endophyte strains that lack either or both of the animal toxins have been introduced into commercial cultivars.
Molecular genetic markers such as simple sequence repeat (SSR) markers have been developed as diagnostic tests to distinguish between endophyte taxa and detect genetic variation within taxa. The markers may be used to discriminate endophyte strains with different toxin profiles.
However, there remains a need for methods of identifying, isolating, characterising and/or modifying endophytes and a need for new endophyte strains having desired properties.
In the fungal kingdom, there is no differentiation of individuals into sexes generating different gametes, but instead mating-type identity is determined by inheritance of alleles at specific mating-type loci.
The mating-type (MAT) genes constitute master regulators of sexual reproduction in filamentous fungi. Although mating-type loci consist of one to a few linked genes, and are thus limited to a small genomic region, alternate sequences at MAT, denoted idiomorphs, lack significant sequence similarity and encode different transcriptional regulators.
Fusion events are required during sexual reproduction in filamentous ascomycete species. Although cell fusion processes associated with vegetative growth as opposed to sexual development serve different developmental functions, both require extracellular communication and chemotropic interactions, followed by cell wall breakdown, membrane-merger and pore formation.
A number of genes have been characterised that are required for both sexual reproduction and vegetative hyphal fusion, including components of the MAPK pathway which is activated in response to pheromone perception during mating. The expression of pheromone precursors and pheromone receptor genes is directly controlled by transcription factors encoded by the mating-type genes.
Hyphal fusion occurs readily within an individual colony during vegetative growth, maintaining the physiological continuity of the organism. Hyphal fusion between different endophyte strains of opposite mating-type may be promoted by treating the mycelia with a combination of cell wall-degrading enzymes and fusion agents such as PEG4000.
However, there remains a need for methods of molecular breeding of endophytes and for new endophyte strains having desired properties.
Neotyphodium endophytes are not only of interest in agriculture, as they are a potential source for bioactive molecules such as insecticides, fungicides, other biocides and bioprotectants, allelochemicals, medicines and nutraceuticals.
Difficulties in artificially breeding of these endophytes limit their usefulness. For example, many of the novel endophytes known to be beneficial to pasture-based agriculture exhibit low inoculation frequencies and are less stable in elite germplasm.
Thus, there remains a need for methods of generating novel, highly compatible endophytes.
There also remains a need for more endophyte strains with desirable properties and for more detailed characterisation of their toxin and metabolic profiles, antifungal activity, stable host associations and their genomes.
It is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties or deficiencies associated with the prior art.
In a first aspect, the present invention provides a method for selecting and/or characterising an endophyte strain, said method including:
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- providing a plurality of samples of endophytes;
- subjecting said endophytes to genetic analysis;
- subjecting said endophytes to metabolic analysis; and
- selecting endophytes having a desired genetic and metabolic profile.
In a preferred embodiment, this aspect of the invention may include the further step of assessing geographic origin of the endophytes and selecting endophytes having a desired genetic and metabolic profile and a desired geographic origin.
In a preferred embodiment, the plurality of samples of endophytes may be provided by a method including:
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- providing a plurality of plant samples; and
- isolating endophytes from said plant samples.
In a preferred embodiment, the method may be performed using an electronic device, such as a computer.
Applicant has surprisingly found that specific detection of endophytes in planta with markers such as SSR markers has provided the tools for efficient assessment of endophyte genetic diversity in diverse grass populations and the potential discovery of novel endophyte strains.
A large scale endophyte discovery program was undertaken to establish a ‘library’ of novel endophyte strains. A collection of perennial ryegrass and tall fescue accessions was established.
Genetic analysis of endophytes in these accessions has lead to the identification of a number of novel endophyte strains. These novel endophyte strains are genetically distinct from known endophyte strains.
Metabolic profiling was undertaken to determine the toxin profile of these strains grown in vitro and/or following inoculation in planta.
Specific detection of endophytes in planta with SSR markers may be used to confirm the presence and identity of endophyte strains artificially inoculated into, for example, grass plants, varieties and cultivars.
The endophytes have been genetically characterised to demonstrate genetic distinction from known endophyte strains and to confirm the identity of endophyte strains artificially inoculated into, for example, grass plants, varieties and cultivars.
By a ‘plurality’ of samples of endophytes or plant samples is meant a number sufficient to enable a comparison of genetic and metabolic profiles of individual endophytes.
Preferably, between approximately 10 and 1,000,000 endophytes are provided, more preferably between approximately 100 and 1,000 endophytes.
Phenotypic screens were established to select for novel ‘designer’ grass-endophyte associations. These screens were for desirable characteristics such as enhanced biotic stress tolerance, enhance drought tolerance and enhanced water use efficiency, and enhanced plant vigour.
Novel ‘designer’ endophytes were generated by targeted methods including polyploidisation and X-ray mutagenesis.
These endophytes may be characterised, for example using antifungal bioassays, in vitro growth rate assays and/or genome survey sequencing (GSS).
Metabolic profiling may also be undertaken to determine the toxin profile of these strains grown in vitro and/or following inoculation in planta.
These endophytes may be delivered into plant germplasm to breed ‘designer’ grass endophyte associations.
Specific detection of endophytes in planta with SSR markers may be used to confirm the presence and identity of endophyte strains artificially inoculated into, for example, grass plants, varieties and cultivars.
The endophytes may be subject to genetic analysis (genetically characterized) to demonstrate genetic distinction from known endophyte strains and to confirm the identity of endophyte strains artificially inoculated into, for example, grass plants, varieties and cultivars.
By ‘genetic analysis’ is meant analysing the nuclear and/or mitochondrial DNA of the endophyte.
This analysis may involve detecting the presence or absence of polymorphic markers, such as simple sequence repeats (SSRs) or mating-type markers. SSRs, also called microsatellites, are based on a 1-7 nucleotide core element, more typically a 1-4 nucleotide core element, that is tandemly repeated. The SSR array is embedded in complex flanking DNA sequences. Microsatellites are thought to arise due to the property of replication slippage, in which the DNA polymerase enzyme pauses and briefly slips in terms of its template, so that short adjacent sequences are repeated. Some sequence motifs are more slip-prone than others, giving rise to variations in the relative numbers of SSR loci based on different motif types. Once duplicated, the SSR array may further expand (or contract) due to further slippage and/or unequal sister chromatid exchange. The total number of SSR sites is high, such that in principle such loci are capable of providing tags for any linked gene.
SSRs are highly polymorphic due to variation in repeat number and are co-dominantly inherited. Their detection is based on the polymerase chain reaction (PCR), requiring only small amounts of DNA and suitable for automation. They are ubiquitous in eukaryotic genomes, including fungal and plant genomes, and have been found to occur every 21 to 65 kb in plant genomes. Consequently, SSRs are ideal markers for a broad range of applications such as genetic diversity analysis, genotypic identification, genome mapping, trait mapping and marker-assisted selection.
Known SSR markers which may be used to investigate endophyte diversity in perennial ryegrass are described in van Zijll de Jong et al (2003).
Alternatively, or in addition, the genetic analysis may involve sequencing genomic and/or mitochondrial DNA and performing sequence comparisons to assess genetic variation between endophytes.
The endophytes may be subject to metabolic analysis to identify the presence of desired metabolic traits.
By ‘metabolic analysis’ is meant analysing metabolites, in particular toxins, produced by the endophytes. Preferably, this is done by generation of inoculated plants for each of the endophytes and measurement of toxin levels in planta. More preferably, this is done by generation of isogenically inoculated plants for each of the endophytes and measurement of toxin levels in planta.
By a ‘desired genetic and metabolic profile’ is meant that the endophyte includes genetic and metabolic characteristics that result in a beneficial phenotype in a plant harbouring, or otherwise associated with, the endophyte.
Such beneficial properties include improved tolerance to water and/or nutrient stress, improved resistance to pests and/or diseases, enhanced biotic stress tolerance, enhanced drought tolerance, enhanced water use efficiency, reduced toxicity and enhanced vigour in the plant with which the endophyte is associated, relative to a control endophyte such as standard toxic (ST) endophyte or to a no endophyte control plant.
For example, tolerance to water and/or nutrient stress may be increased by at least approximately 5%, more preferably at least approximately 10%, more preferably at least approximately 25%, more preferably at least approximately 50%, more preferably at least approximately 100%, relative to a control endophyte such as standard toxic (ST) endophyte or to no endophyte control plant. Preferably, tolerance to water and/or nutrient stress may be increased by between approximately 5% and approximately 50%, more preferably between approximately 10% and approximately 25%, relative to a control endophyte such as ST or to a no endophyte control plant.
Such beneficial properties also include reduced toxicity of the associated plant to grazing animals.
For example, toxicity may be reduced by at least approximately 5%, more preferably at least approximately 10%, more preferably at least approximately 25%, more preferably at least approximately 50%, more preferably at least approximately 100%, relative to a control endophyte such as ST endophyte. Preferably, toxicity may be reduced by between approximately 5% and approximately 100%, more preferably between approximately 50% and approximately 100% relative to a control endophyte such as ST endophyte.
In a preferred embodiment toxicity may be reduced to a negligible amount or substantially zero toxicity.
For example, water use efficiency and/or plant vigour may be increased by at least approximately 5%, more preferably at least approximately 10%, more preferably at least approximately 25%, more preferably at least approximately 50%, more preferably at least approximately 100%, relative to a control endophyte such as ST or to a no endophyte control plant. Preferably, tolerance to water and/or nutrient stress may be increased by between approximately 5% and approximately 50%, more preferably between approximately 10% and approximately 25%, relative to a control endophyte such as ST or to a no endophyte control plant.
The methods of the present invention may be applied to a variety of plants. In a preferred embodiment, the methods may be applied to grasses, preferably forage, turf or bioenergy grasses such as those of the genera Lolium and Festuca, including L. perenne (perennial ryegrass) and L. arundinaceum (tall fescue).
The methods of the present invention may be applied to a variety of endophytes. In a preferred embodiment, the methods may be applied to fungi of the genus Neotyphodium, including N. lolii and N. coenophialum. In another preferred embodiment, the methods may be applied to fungi of the genus Epichloë, including E. festucae and E. typhina. However, the methods may also be used to identify endophytes of previously undescribed taxa.
Applicants have surprisingly found that endophyte E1 is a genetically novel, non-Neotyphodium lolii, endophyte. E1 is representative of an as yet un-named taxon. This finding is supported by mitochondrial and nuclear genome sequence analysis.
While applicants do not wish to be restricted by theory, on the basis of DNA specific content, the predicted alkaloid profile of E1 indicates that lolitrem B toxins deleterious to animal health are not produced by this endophyte. Endophyte E1 has the mating-type MAT1-1, the opposite mating-type to that carried by the N. lolii endophytes previously characterized. Endophyte E1 also has a high inoculation success rate in perennial ryegrass as compared to other endophytes.
Accordingly, in a second aspect, the present invention provides a substantially purified or isolated endophyte selected from the group consisting of E1, NEA10, NEA11 and NEA12, which were deposited at The National Measurement Institute, 1/153 Bertie Street, Port Melbourne, Victoria, Australia, 3207, on 5 Jan. 2010 with accession numbers V10/000001, V10/000002, V10/000003 and V10/000004, respectively. Replacement deposits were made on Apr. 15, 2016 in response to a notification of non-viability, and were assigned the same accession numbers.
The present invention also provides a substantially purified or isolated endophyte selected from the group consisting of NEA13 and NEA14, which were deposited at the National Measurement Institute, 1/153 Bertie Street, Port Melbourne, Victoria, Australia, 3207, on 23 Dec. 2010 with accession numbers V10/030285 and V10/030284, respectively. Replacement deposits were made on Apr. 15, 2016 in response to a notification of non-viability, and were assigned the same accession numbers.
In a further aspect the present invention provides a substantially purified or isolated endophyte having a desired toxin profile. Preferably the endophyte is isolated from a fescue species, preferably tall fescue. Preferably, the endophyte is of the genus Neotyphodium, more preferably it is from a species selected from the group consisting of N. uncinatum, N. coenophialum and N. lolii, most preferably N. coenophialum. The endophyte may also be from the genus Epichloe, including E. typhina, E. baconii and E. festucae. The endophyte may also be of the non-Epichloe out-group. The endophyte may also be from a species selected from the group consisting of FaTG-3 and FaTG-3 like, and FaTG-2 and FaTG-2 like.
By a ‘desired toxin profile’ is meant that the endophyte produces significantly less toxic alkaloids, such as ergovaline, compared with a plant inoculated with a control endophyte such as standard toxic (ST) endophyte; and/or significantly more alkaloids conferring beneficial properties such as improved tolerance to water and/or nutrient stress and improved resistance to pests and/or diseases in the plant with which the endophyte is associated, such as peramine, N-formylloline, N-acetylloline and norloline, again when compared with a plant inoculated with a control endophyte such as ST or with a no endophyte control plant.
For example, toxic alkaloids may be present in an amount less than approximately 11.1 g/g dry weight, for example between approximately 1 and 0.001 μg/g dry weight, preferably less than approximately 0.5 μg/g dry weight, for example between approximately 0.5 and 0.001 μg/g dry weight, more preferably less than approximately 0.2 μg/g dry weight, for example between approximately 0.2 and 0.001 μg/g dry weight.
For example, said alkaloids conferring beneficial properties may be present in an amount of between approximately 5 and 100 μg/g dry weight, preferably between approximately 10 and 50 μg/g dry weight, more preferably between approximately 15 and 30 μg/g dry weight.
In a particularly preferred embodiment, the present invention provides a substantially purified or isolated endophyte selected from the group consisting of NEA16, NEA17, NEA18, NEA19, NEA20, NEA21 and NEA23, which were deposited at The National Measurement Institute, 1/153 Bertie Street, Port Melbourne, Victoria, Australia, 3207, on 3 Apr. 2012 with accession numbers V12/001413, V12/001414, V12/001415, V12/001416, V12/001417, V12/001418 and V12/001419, respectively. Replacement deposits were made on Apr. 15, 2016 in response to a notification of non-viability, and were assigned the same accession numbers. Such endophytes may have a desired toxin profile as hereinbefore described.
In a further aspect the present invention provides an endophyte variant having a desired genetic and metabolic profile. Preferably the endophyte variant is generated by polyploidisation or induced chromosome doubling, for example by treating the endophyte with colchicine or a similar compound. Alternatively, the endophyte variant may be generated by X-ray mutagenesis or exposing the endophyte to ionising radiation, for example from a caesium source.
Preferably the endophyte which is treated to generate the endophyte variant is isolated from a Lolium species, preferably Lolium perenne. Preferably, the endophyte is of the genus Neotyphodium, more preferably it is from a species selected from the group consisting of N uncinatum, N coenophialum and N lolii, most preferably N lolii. The endophyte may also be from the genus Epichloe, including E typhina, E baconii and E festucae. The endophyte may also be of the non-Epichloe out-group. The endophyte may also be from a species selected from the group consisting of FaTG-3 and FaTG-3 like, and FaTG-2 and FaTG-2 like.
In a preferred embodiment, the endophyte variant may have a desired toxin profile. By a ‘desired toxin profile’ is meant that the endophyte produces significantly less toxic alkaloids, such as ergovaline, compared with a plant inoculated with a control endophyte such as standard toxic (ST) endophyte; and/or significantly more alkaloids conferring beneficial properties such as improved resistance to pests and/or diseases in the plant with which the endophyte is associated, such as peramine, N-formylloline, N-acetylloline and norloline, again when compared with a plant inoculated with a control endophyte such as ST or with a no endophyte control plant.
For example, toxic alkaloids may be present in an amount less than approximately 11.1 g/g dry weight, for example between approximately 1 and 0.001 μg/g dry weight, preferably less than approximately 0.5 μg/g dry weight, for example between approximately 0.5 and 0.001 μg/g dry weight, more preferably less than approximately 0.2 μg/g dry weight, for example between approximately 0.2 and 0.001 μg/g dry weight.
For example, said alkaloids conferring beneficial properties may be present in an amount of between approximately 5 and 100 μg/g dry weight, preferably between approximately 10 and 50 μg/g dry weight, more preferably between approximately 15 and 30 μg/g dry weight.
In a particularly preferred embodiment, the present invention provides an endophyte variant selected from the group consisting of NEA12dh5, NEA12dh6, NEA12dh13, NEA12dh14, and NEA12dh17, which were deposited at The National Measurement Institute, 1/153 Bertie Street, Port Melbourne, Victoria, Australia, 3207, on 3 Apr. 2012 with accession numbers V12/001408, V12/001409, V12/001410, V12/001411 and V12/001412, respectively. Replacement deposits were made on Apr. 15, 2016 in response to a notification of non-viability, and were assigned the same accession numbers. Such endophytes may have a desired genetic and metabolic profile as hereinbefore described.
In a preferred embodiment, the endlphyte may be substantially purified.
By ‘substantially purified’ is meant that the endophyte is free of other organisms. The term therefore includes, for example, an endophyte in axenic culture. Preferably, the endophyte is at least approximately 90% pure, more preferably at least approximately 95% pure, even more preferably at least approximately 98% pure.
The term ‘isolated’ means that the endophyte is removed from its original environment (eg. the natural environment if it is naturally occurring). For example, a naturally occurring endophyte present in a living plant is not isolated, but the same endophyte separated from some or all of the coexisting materials in the natural system, is isolated.
On the basis of the deposits referred to above, the entire genome of an endophyte selected from the group consisting of E1, NEA10, NEA11, NEA12, NEA13, NEA14, NEA21, NEA23, NEA18, NEA19, NEA16, NEA20, NEA12dh5, NEA12dh6, NEA12dh13, NEA12dh14 and NEA12dh17, is incorporated herein by reference.
Thus, in a further aspect, the present invention includes identifying and/or cloning nucleic acids including genes encoding polypeptides or transcription factors, for example transcription factors that are involved in sexual reproduction or vegetative hyphal fusion, in an endophyte. For example, the nucleic acids may encode mating-type genes, such as MAT1-1.
Methods for identifying and/or cloning nucleic acids encoding such genes are known to those skilled in the art and include creating nucleic acid libraries, such as cDNA or genomic libraries, and screening such libraries, for example using probes for genes of the desired type, for example mating-type genes; or mutating the genome of the endophyte of the present invention, for example using chemical or transposon mutagenesis, identifying changes in the production of polypeptides or transcription factors of interest, for example those that are involved in sexual reproduction or vegetative hyphal fusion, and thus identifying genes encoding such polypeptides or transcription factors.
Thus, in a further aspect of the present invention, there is provided a substantially purified or isolated nucleic acid encoding a polypeptide or transcription factor from the genome of an endophyte of the present invention. Preferably, the nucleic acid may encode a polypeptide or transcription factor that is involved in sexual reproduction or vegetative hyphal fusion in an endophyte.
In a preferred embodiment, the nucleic acid may include a mating-type gene, such as MAT1-1, or a functionally active fragment or variant thereof.
In a particularly preferred embodiment, the nucleic acid may include a nucleotide sequence selected from the group consisting of sequences shown in
By ‘nucleic acid’ is meant a chain of nucleotides capable of carrying genetic information. The term generally refers to genes or functionally active fragments or variants thereof and or other sequences in the genome of the organism that influence its phenotype. The term ‘nucleic acid’ includes DNA (such as cDNA or genomic DNA) and RNA (such as mRNA or microRNA) that is single- or double-stranded, optionally containing synthetic, non-natural or altered nucleotide bases, synthetic nucleic acids and combinations thereof.
By a ‘nucleic acid encoding a polypeptide or transcription factor’ is meant a nucleic acid encoding an enzyme or transcription factor normally present in an endophyte of the present invention.
By a ‘nucleic acid encoding a polypeptide or transcription factor involved sexual reproduction or vegetative hyphal fusion’ is meant a nucleic acid encoding an enzyme or transcription factor normally present in an endophyte of the present invention, which catalyses or regulates a step involved in sexual reproduction or vegetative hyphal fusion in the endophyte, or otherwise regulates sexual reproduction or vegetative hyphal fusion in the endophyte.
The present invention encompasses functionally active fragments and variants of the nucleic acids of the present invention. By ‘functionally active’ in relation to the nucleic acid is meant that the fragment or variant (such as an analogue, derivative or mutant) is capable of manipulating the function of the encoded polypeptide, for example by being translated into an enzyme or transcription factor that is able to catalyse or regulate a step involved in the relevant pathway, or otherwise regulate the pathway in the endophyte. For example, the fragment or variant may be capable of manipulating sexual reproduction or vegetative hyphal fusion in an endophyte, for example by being translated into an enzyme or transcription factor that is able to catalyse or regulate a step involved in sexual reproduction or vegetative hyphal fusion in the endophyte, or otherwise regulate sexual reproduction or vegetative hyphal fusion in the endophyte.
Such variants include naturally occurring allelic variants and non-naturally occurring variants. Additions, deletions, substitutions and derivatizations of one or more of the nucleotides are contemplated so long as the modifications do not result in loss of functional activity of the fragment or variant. Preferably the functionally active fragment or variant has at least approximately 80% identity to the relevant part of the above mentioned sequence to which the fragment or variant corresponds, more preferably at least approximately 90% identity, even more preferably at least approximately 95% identity, most preferably at least approximately 98% identity. Such functionally active variants and fragments include, for example, those having conservative nucleic acid changes. Examples of suitable nucleic acid changes are also shown in
Preferably the fragment has a size of at least 20 nucleotides, more preferably at least 50 nucleotides, more preferably at least 100 nucleotides.
By ‘conservative nucleic acid changes’ is meant nucleic acid substitutions that result in conservation of the amino acid in the encoded protein, due to the degeneracy of the genetic code. Such functionally active variants and fragments also include, for example, those having nucleic acid changes which result in conservative amino acid substitutions of one or more residues in the corresponding amino acid sequence.
By ‘conservative amino acid substitutions’ is meant the substitution of an amino acid by another one of the same class, the classes being as follows:
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- Nonpolar: Ala, Val, Leu, Ile, Pro, Met, Phe, Trp
- Uncharged polar: Gly, Ser, Thr, Cys, Tyr, Asn, Gln
- Acidic: Asp, Glu
- Basic: Lys, Arg, His
Other conservative amino acid substitutions may also be made as follows:
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- Aromatic: Phe, Tyr, His
- Proton Donor: Asn, Gln, Lys, Arg, His, Trp
- Proton Acceptor: Glu, Asp, Thr, Ser, Tyr, Asn, Gln
In a further aspect of the present invention, there is provided a genetic construct including a nucleic acid according to the present invention.
By ‘genetic construct’ is meant a recombinant nucleic acid molecule.
In a preferred embodiment, the genetic construct according to the present invention may be a vector.
By a ‘vector’ is meant a genetic construct used to transfer genetic material to a target cell.
The vector may be of any suitable type and may be viral or non-viral. The vector may be an expression vector. Such vectors include chromosomal, non-chromosomal and synthetic nucleic acid sequences, eg. derivatives of plant viruses; bacterial plasmids; derivatives of the Ti plasmid from Agrobacterium tumefaciens; derivatives of the Ri plasmid from Agrobacterium rhizogenes; phage DNA; yeast artificial chromosomes; bacterial artificial chromosomes; binary bacterial artificial chromosomes; vectors derived from combinations of plasmids and phage DNA. However, any other vector may be used as long as it is replicable or integrative or viable in the target cell.
In a preferred embodiment of this aspect of the invention, the genetic construct may further include a promoter and a terminator; said promoter, gene and terminator being operatively linked.
By a ‘promoter’ is meant a nucleic acid sequence sufficient to direct transcription of an operatively linked nucleic acid sequence.
By ‘operatively linked’ is meant that the nucleic acid(s) and a regulatory sequence, such as a promoter, are linked in such a way as to permit expression of said nucleic acid under appropriate conditions, for example when appropriate molecules such as transcriptional activator proteins are bound to the regulatory sequence. Preferably an operatively linked promoter is upstream of the associated nucleic acid.
By ‘upstream’ is meant in the 3′->5′ direction along the nucleic acid.
The promoter and terminator may be of any suitable type and may be endogenous to the target cell or may be exogenous, provided that they are functional in the target cell.
A variety of terminators which may be employed in the genetic constructs of the present invention are also well known to those skilled in the art. The terminator may be from the same gene as the promoter sequence or a different gene. Particularly suitable terminators are polyadenylation signals, such as the (CaMV)35S polyA and other terminators from the nopaline synthase (nos) and the octopine synthase (ocs) genes.
The genetic construct, in addition to the promoter, the gene and the terminator, may include further elements necessary for expression of the nucleic acid, in different combinations, for example vector backbone, origin of replication (ori), multiple cloning sites, spacer sequences, enhancers, introns (such as the maize Ubiquitin Ubi intron), antibiotic resistance genes and other selectable marker genes [such as the neomycin phosphotransferase (nptII) gene, the hygromycin phosphotransferase (hph) gene, the phosphinothricin acetyltransferase (bar or pat) gene], and reporter genes [such as beta-glucuronidase (GUS) gene (gusA) and the green fluorescent protein (GFP) gene (gfp)]. The genetic construct may also contain a ribosome binding site for translation initiation. The genetic construct may also include appropriate sequences for amplifying expression.
Those skilled in the art will appreciate that the various components of the genetic construct are operably linked, so as to result in expression of said nucleic acid. Techniques for operably linking the components of the genetic construct of the present invention are well known to those skilled in the art. Such techniques include the use of linkers, such as synthetic linkers, for example including one or more restriction enzyme sites.
Preferably, the genetic construct is substantially purified or isolated.
By ‘substantially purified’ is meant that the genetic construct is free of the genes, which, in the naturally-occurring genome of the organism from which the nucleic acid or promoter of the invention is derived, flank the nucleic acid or promoter. The term therefore includes, for example, a genetic construct which is incorporated into a vector; into an autonomously replicating plasmid or virus; or into the genomic DNA of a prokaryote or eukaryote; or which exists as a separate molecule (eg. a cDNA or a genomic or cDNA fragment produced by PCR or restriction endonuclease digestion) independent of other sequences. It also includes a genetic construct which is part of a hybrid gene encoding additional polypeptide sequence.
Preferably, the substantially purified genetic construct is at least approximately 90% pure, more preferably at least approximately 95% pure, even more preferably at least approximately 98% pure.
The term “isolated” means that the material is removed from its original environment (eg. the natural environment if it is naturally occurring). For example, a naturally occurring nucleic acid present in a living plant is not isolated, but the same nucleic acid separated from some or all of the coexisting materials in the natural system, is isolated. Such nucleic acids could be part of a vector and/or such nucleic acids could be part of a composition, and still be isolated in that such a vector or composition is not part of its natural environment.
As an alternative to use of a selectable marker gene to provide a phenotypic trait for selection of transformed host cells, the presence of the genetic construct in transformed cells may be determined by other techniques well known in the art, such as PCR (polymerase chain reaction), Southern blot hybridisation analysis, histochemical assays (e.g. GUS assays), thin layer chromatography (TLC), northern and western blot hybridisation analyses.
The genetic constructs of the present invention may be introduced into plants or fungi by any suitable technique. Techniques for incorporating the genetic constructs of the present invention into plant cells or fungal cells (for example by transduction, transfection, transformation or gene targeting) are well known to those skilled in the art. Such techniques include Agrobacterium-mediated introduction, Rhizobium-mediated introduction, electroporation to tissues, cells and protoplasts, protoplast fusion, injection into reproductive organs, injection into immature embryos and high velocity projectile introduction to cells, tissues, calli, immature and mature embryos, biolistic transformation, Whiskers transformation, and combinations thereof. The choice of technique will depend largely on the type of plant or fungus to be transformed, and may be readily determined by an appropriately skilled person. For transformation of protoplasts, PEG-mediated transformation is particularly preferred. For transformation of fungi PEG-mediated transformation and electroporation of protoplasts and Agrobacterium-mediated transformation of hyphal explants are particularly preferred.
Cells incorporating the genetic constructs of the present invention may be selected, as described below, and then cultured in an appropriate medium to regenerate transformed plants or fungi, using techniques well known in the art. The culture conditions, such as temperature, pH and the like, will be apparent to the person skilled in the art. The resulting plants or fungi may be reproduced, either sexually or asexually, using methods well known in the art, to produce successive generations of transformed plants or fungi. In a further aspect, the present invention provides a plant inoculated with an endophyte or endophyte variant as hereinbefore described, said plant comprising an endophyte-free host plant stably infected with said endophyte or endophyte variant.
Preferably, the plant is infected with the endophyte or endophyte variant by a method selected from the group consisting of inoculation, breeding, crossing, hybridization and combinations thereof.
In a preferred embodiment, the plant may be infected by isogenic inoculation. This has the advantage that phenotypic effects of endophytes may be assessed in the absence of host-specific genetic effects. More particularly, multiple inoculations of endophytes may be made in plant germplasm, and plantlets regenerated in culture before transfer to soil.
The identification of an endophyte of the opposite mating-type that is highly compatible and stable in planta provides a means for molecular breeding of endophytes for perennial ryegrass. Preferably the plant may be infected by hyper-inoculation.
Hyphal fusion between endophyte strains of the opposite mating-type provides a means for delivery of favourable traits into the host plant, preferably via hyper-inoculation. Such strains are preferably selected from the group including an endophyte strain that exhibits the favourable characteristics of high inoculation frequency and high compatibility with a wide range of germplasm, preferably elite perennial ryegrass and/or tall fescue host germplasm and an endophyte that exhibits a low inoculation frequency and low compatibility, but has a highly favourable alkaloid toxin profile.
It has generally been assumed that interactions between endophyte taxa and host grasses will be species specific. Applicants have surprisingly found that endophyte from tall fescue may be used to deliver favourable traits to ryegrasses, such as perennial ryegrass.
In a further aspect of the present invention there is provided a method of analysing metabolites in a plurality of endophytes, said method including:
-
- providing:
- a plurality of endophytes; and
- a plurality of isogenic plants;
- inoculating each isogenic plant with an endophyte;
- culturing the endophyte-infected plants; and
- analysing the metabolites produced by the endophyte-infected plants.
- providing:
By ‘metabolites’ is meant chemical compounds, in particular toxins, produced by the endophyte-infected plant, including, but not limited to, lolines, peramine, ergovaline, lolitrem, and janthitrems, such as janthitrem I, janthitrem G and janthitem F.
By Isogenic plants' is meant that the plants are genetically identical.
The endophyte-infected plants may be cultured by known techniques. The person skilled in the art can readily determine appropriate culture conditions depending on the plant to be cultured.
The metabolites may be analysed by known techniques such as chromatographic techniques or mass spectrometry, for example LCMS or HPLC. In a particularly preferred embodiment, endophyte-infected plants may be analysed by reverse phase liquid chromatography mass spectrometry (LCMS). This reverse phase method may allow analysis of specific metabolites (including lolines, peramine, ergovaline, lolitrem, and janthitrems, such as janthitrem I, janthitrem G and janthitem F) in one LCMS chromatographic run from a single endophyte-infected plant extract.
In another particularly preferred embodiment, LCMS including EIC (extracted ion chromatogram) analysis may allow detection of the alkaloid metabolites from small quantities of endophyte-infected plant material. Metabolite identity may be confirmed by comparison of retention time with that of pure toxins or extracts of endophyte-infected plants with a known toxin profile analysed under substantially the same conditions and/or by comparison of mass fragmentation patterns, for example generated by MS2 analysis in a linear ion trap mass spectrometer.
In a particularly preferred embodiment, the endophytes may be selected from the group consisting of E1, NEA10, NEA11, NEA12, NEA13, NEA14, NEA21, NEA23, NEA18, NEA19, NEA16 and NEA20.
In a particularly preferred embodiment, the endophyte variant may be selected from the group consisting of NEA12dh5, NEA12dh6, NEA12dh13, NEA12dh14, and NEA12dh17.
In a further aspect, the present invention provides a plant, plant seed or other plant part derived from a plant of the present invention and stably infected with an endophyte or endophyte variant of the present invention.
Preferably, the plant cell, plant, plant seed or other plant part is a grass, more preferably a forage, turf or bioenergy grass, such as those of the genera Lolium and Festuca, including L. perenne and L. arundinaceum.
By ‘plant cell’ is meant any self-propagating cell bounded by a semi-permeable membrane and containing plastid. Such a cell also required a cell wall if further propagation is desired. Plant cell, as used herein includes, without limitation, seeds suspension cultures, embryos, meristematic regions, callus tissue, leaves, roots, shoots, gametophytes, sporophytes, pollen and microspores.
In a further aspect, the present invention provides use of an endophyte or endophyte variant as hereinbefore described to produce a plant stably infected with said endophyte or endophyte variant.
In a still further aspect, the present invention provides a method of quantifying endophyte content of a plant, said method including measuring copies of a target sequence by quantitative PCR.
In a preferred embodiment, the method may be performed using an electronic device, such as a computer.
Preferably, quantitative PCR may be used to measure endophyte colonisation in planta, for example using a nucleic acid dye, such as SYBR Green chemistry, and qPCR-specific primer sets. The primer sets may be directed to a target sequence such as an endophyte gene, for example the peramine biosynthesis perA gene.
The development of a high-throughput PCR-based assay to measure endophyte biomass in planta may enable efficient screening of large numbers of plants to study endophyte-host plant biomass associations.
As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps.
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.
In the figures:
1 peramine (MW 247.3);
2 ergovaline (MW 533.6);
3 lolitrem B (MW 685.9);
4 janthitrem I (MW 645.8);
5 janthitrem G (MW 629.8);
6 janthitrem F (MW 645.8).
A. peramine
-
- NL: 7.47E4
- Base Peak m/z=47.50-248.50 F: ITMS+c ESI Full ms
- [150.00-2000.00] MS
B. ergovaline - NL: 1.64E6
- Base Peak m/z=533.40-534.40 F: ITMS+c ESI Full ms
- [150.00-2000.00] MS
C. lolitrem B
Base Peak m/z=685.50-687.00 F: ITMS+c ESI Full ms
[150.00-2000.00] MSA. AR37 no peramine
-
- NL: 3.14E3
- Base Peak m/z=247.50-248.50 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
B. AR37 no ergovaline - NL: 7.39E4
- Base Peak m/z=533.40-534.40 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
C. AR37 no lolitrem B - NL: 1.32E4
- Base Peak m/z=685.50-687.00 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
D. AR37 janthitrem - NL: 8.68E4
- Base Peak m/z=645.50-646.50 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
E. NEA12 no peramine - NL: 6.18E3
- Base Peak m/z=247.50-248.50 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
F. NEA12 no ergovaline - NL: 4.10E3
- Base Peak m/z=533.40-534.40 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
G. NEA12 no lolitrem B - NL: 1.32E4
- Base Peak m/z=685.50-687.00 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
H. NEA12 janthitrem - NL: 1.04E4
- Base Peak m/z=645.50-646.50 F: ITMS+c ESI
- Full ms [150.00-2000.00] MS
A collection of 244 perennial grass accessions was assembled for the discovery of novel endophyte strains. The collection targeted accessions from the Northern Mediterranean and Eastern Europe for endophytes that lack lolitrems, as well as accessions from the Middle East, the proposed centre of origin of perennial ryegrass and N. lolii.
Genotypic analysis of endophyte content was performed across a total of 189 accessions. From each accession 1-5 plant genotypes were analysed for endophyte. Endophyte incidence was low, with endophyte detected in 51% of accessions. Endophyte was consistently detected (with 0 SSR markers) in 77 of the accessions.
Endophytes representing five different taxa were detected across the 77 accessions with 18 SSR markers used to investigate endophyte diversity in perennial ryegrass (
Genetic variation in N. lolii appeared to be low. A total of 22 unique genotypes were detected across the 63 accessions host to N. lolii.
The likely toxin profiles of 14 of the 22 genotypes were established from comparisons with genetic and phenotypic data from previous studies. Most of these genotypes (12/14) showed genetic similarity to endophytes known to produce lolitrems.
There were two genotypes that showed genetic similarity to genotypes known to lack lolitrems but produce ergovaline. One of these genotypes was identical to the genotype detected in the endophyte NEA6. The likely toxin profiles of the remaining eight genotypes were not known. These genotypes did not show high levels of genetic similarity to the endophytes AR1, Endosafe, NEA3 or NEA5.
Plants carrying candidate endophytes were subjected to primary metabolic profiling in the endogenous genetic background, through clonal propagation and measurement of toxin levels. A total of 42 genotypes representing four of the five taxa were selected for toxin profiling, including the eight novel genotypes with unknown toxin profiles. The perennial ryegrass genotype North African 6 (NA6), which contains standard toxic (ST) endophyte, was used as a control.
For metabolic profiling, a complete randomised block design was used, with four replicate clones for each plant and using four hydroponics tubs as blocks. Following three months in hydroponics, whole shoot (leaf plus basal region) was harvested from each plant. The fresh and dry weights of each plant were measured and powdered sample material from 80 (20 genotypes×4 replicates) samples (three tillers per sample) analysed for alkaloid content (lolitrem, ergovaline and peramine).
EXAMPLE 2—CANDIDATE ENDOPHYTESCandidate endophytes for further study were chosen on the basis of their genetic identity and metabolic profile. Host-endophyte combinations producing significant amounts of lolitrem B were eliminated, as the ryegrass staggers syndrome produced by this alkaloid is the most important limitation for livestock production.
The candidate endophyte NEA10 (originating from Spain) was identified as a novel genotype in this analysis with an unknown toxin profile. Its genetic identity is a unique N. lolii strain. Following in planta metabolic profiling analysis, candidate endophyte NEA10 was found to produce ergovaline and peramine, and not lolitrem B.
The candidate endophyte NEA11 (originating from France) was identified as a novel genotype in this analysis with an unknown toxin profile. Its genetic identity is a unique LpTG-2 strain. Following in planta metabolic profiling analysis, candidate endophyte NEA11 was found to produce ergovaline and peramine, and not lolitrem B.
The candidate endophyte NEA12 (originating from France) was identified as a novel genotype in this analysis with an unknown toxin profile. NEA12 is a genetically novel, non-Neotyphodium lolii, endophyte representative of an as yet un-named taxon. Following in planta metabolic profiling analysis, candidate endophyte NEA12 was found to not produce the three alkaloids assessed (lolitrem B, ergovaline and peramine).
The candidate endophyte E1 was identified as a novel genotype in this analysis with an unknown toxin profile. E1 is a genetically novel, non-Neotyphodiumlolii, endophyte representative of an as yet un-named taxon. Following in planta metabolic profiling analysis, candidate endophyte E1 was found to not produce the three alkaloids assessed (lolitrem B, ergovaline and peramine).
EXAMPLE 3—METHODOLOGIES FOR ENDOPHYTE CHARACTERISATION Endophyte IsolationNovel candidate endophytes were isolated from their host plant to establish an in vitro culture. Following isolation, the genotype of each endophyte was confirmed by SSR analysis to ensure a high level of quality control prior to inception of isogenic inoculations.
Establishment of Meristem Cultures for a Diverse Perennial Ryegrass Host PanelA set of cultivars representing elite germplasm were obtained, including forage and turf types. Meristem cultures from different cultivars were established to evaluate and compare the phenotypic properties of novel endophyte strains in diverse isogenic host backgrounds. Embryogenic genotypes were identified for each of the cultivars through callus induction and proliferation. Subsequent regeneration of embryogenic genotypes identified primary tissue culture responsive (pTCR) genotypes for each of the cultivars. The number of pTCR genotypes with regeneration frequencies ranging from 80-100% varied from 1-4 per cultivar. pTCR genotypes were then prepared for meristem-derived callus induction to identify highly regenerable genotypes for isogeneic endophyte inoculation. Table 1 shows a selection of cultivars developed, and the tissue culture responsive (TCR) genotype, used for isogenic inoculation.
In order to accurately determine the phenotypic effects of different candidate endophytes in the absence of host-specific genetic effects, a system for isogenic inoculation was developed (
A quantitative score was used to assess endophyte inoculation frequency (Table 2). Three diagnostic SSR markers were used to determine endophyte presence and identity and samples were scored on a scale of 0-3.
Of the 570 inoculations tested, 195 (34.2%) could be positively scored with a high degree of confidence (Table 3). Successful inoculations are listed on Table 3.
Variation in inoculation success according to candidate endophyte identity was observed (Table 3). Endophyte NEA10 (2.2%), for example, exhibited relatively lower success rates as compared to NEA11 (67.2%), or the commercial endophyte ST (39.8%; Table 4) and only formed stable associations with one of the five hosts in the panel (Impact). Endophyte E1 is a highly compatible endophyte, which obtained a high rate of success of inoculation into perennial ryegrass (Table 3) compared to other endophytes examined, including the strain ST.
Variation was also observed between host plant genotypes for successful inoculations (Table 3). Tolosa (20.0%) appears to be more recalcitrant to inoculation compared to host plants such as Bronsyn (42.3%) and Impact (49.3%).
Vegetative Stability of Isogenic Perennial Ryegrass-Fungal Endophyte AssociationsFully confirmed endophyte positive plants from the targeted host-endophyte panel (host plants Bealey, Bronsyn, Barsandra, Tolosa and Impact; endophytes ST, NEA10, NEA11, NEA12) were retested 6-12 months after inoculation and 18-24 months after inoculation, to confirm the presence of endophyte and to assess vegetative stability. In this experiment, 3 replicates of 3 tillers each (total of 9 tillers) were collected for SSR-based analysis.
Most of the previously confirmed endophyte positive plants were again confirmed in this study at 6-12 months post inoculation, indicating that each of the host-endophyte combinations were stable (Table 4). Endophyte NEA12 appears to be less stable in planta, as 7 of the 13 previously confirmed samples could not be fully confirmed in this experiment (Table 4). ST also showed lower levels of stability compared to NEA11, with 7/21 samples not re-confirmed in this study (Table 4). Following this analysis, up to three independent inoculation events from each host plant-endophyte combination were retained for further study.
At 18-24 months post inoculation, plants were further assessed for long term vegetative stability (Table 4). ST, NEA10 and NEA11 each exhibit stable associations, with most plants retaining endophyte. NEA12 appears to be less stable in some associations, however does form stable long term associations with Tolosa.
Metabolic profiling was conducted to determine the stability of the predicted endophyte phenotype in a range of different host genotype backgrounds. Four replicates of three tillers each were grown under optimal conditions in hydroponics for six weeks prior to measuring lolitrem B, ergovaline and peramine levels. Each replicate plant was also tested for the presence/identity of endophyte using SSR-based genotyping in order to correlate toxin profile with endophyte presence, in particular for those instances were toxin profiles were negative for the alkaloids measured.
Table 5 summarises the outcomes of metabolic profiling in hydroponics for both the endophyte discovery phase and the isogenic inoculation phase. Toxin profiles were as predicted from the cluster assignment of the endophyte in the diversity analysis and the toxin profiles measured in the endogenous host plant.
Genome Survey Sequencing was performed for non-N. lolii strains NEA12 and E1, LpTG-2 strain NEA11 and Neotyphodium lolii strains including Standard Toxic (ST) and NEA10 using GSFLX Titanium (TI-GSFLX) pyrosequencing technology (Roche; as per manufacturers instructions). A further five N. lolii strains were sequenced using either GSFLX Standard or GS20 pyrosequencing technology. Genome assembly for each of the strains was conducted with GSFLX De Novo Assembler (Table 6).
A new genome assembly was performed for N. lolii strain ST (GSFLX De Novo Assembler), combining sequence reads from both GSFLX and TI-GSFLX runs. Table 7 compares the assembly of single and multiple strains. This combined assembly of the ST genome achieves c.12× coverage of the c.32 Mbp haploid genome. The genome is assembled into 7,875 large contigs (0.5 to 47 kb) of which the net length is 31,750,111 bp.
Analysis using Augustus gene prediction software trained for Fusarium graminearum shows that there are 11,517 predicted protein coding genes in the N. lolii genome.
The content of genes known to be involved in alkaloid production in each of the sequenced endophyte genomes was investigated. Sequence reads for each of the strains were subjected to a BLAST(N) search against each of the known toxin gene sequences (downloaded from NCBI) to determine the degree of gene coverage by sequence reads. Table 8 below shows the correlation between secondary metabolite production and toxin-related gene content in endophyte genomes.
Based on this analysis, endophyte strain E1 is predicted to produce the alkaloids peramine and ergovaline, but not loline or lolitrem B. In planta analysis of alkaloid content has shown that E1 does indeed not produce loline or lolitrem B.
NEA10 and NEA11 produce ergovaline and peramine, but not lolitrem B. The NEA11 sequence provides evidence for 2 peramine biosynthesis genes, as might be expected in a heteroploid genome.
NEA12, known to lack production of ergot alkaloids and lolitrem B, also lacks corresponding biosynthetic genes.
Nuclear Genome ComparisonComparison of the NEA12 Nuclear Genome to E. festucae E2368 and N. Lolii ST
To compare the nuclear genome of NEA12 to E. festucae and N. lolii, the contigs derived from NEA12 were split into 250 bp segments and these segments were used as BLAST(N) queries against E. festucae strain E2368 (University of Kentucky, http://www.genome.ou.edu.fungi.html) and N. lolii ST contigs. One hit was scored for each 250 bp contig if it was greater than 50 bp long and greater than 80% identity. Summary statistics were taken for NEA12 250 bp fragments against E. festucae and N. lolii (
The number of hits showing a given percent identity shows there are more 250 bp segments that give 100 percent identity matches against an E. festucae genome than a N. lolii genome.
The above statistic is independent of the length of the overlap. An identical 250 bp region would give a 250 bp overlap with a percent identity of 100. The number and proportion of these identical reads is given for the two searches below (Table 9).
There are also segments that have no match to either N. lolii (6051) or E. festucae (5670). These data suggest that NEA12 is a new endophyte taxon that is genetically closer to E. festucae than N. lolii. This data supports the earlier observation, using SSR-based genetic diversity analysis, that NEA12 is genetically distinct from N. lolii and E. festucae.
Comparison of E1 Nuclear Genome to NEA12, E. Festucae E2368 and N. lolii ST
For comparison at the whole genome level, the contigs from endophyte strain E1 were split into 123,258 250 bp segments. Each 250 bp segment was used as a BLAST(N) query against the assembled whole genome DNA sequences from NEA12, E. festucae E2368 and N. lolii ST (
The assembled contigs from NEA12 sum to c.17.3 Mb, so the level of sequence similarity to that endophyte is probably underestimated due to limited scope for comparison. If the similarity is expressed as a fraction of the total matches observed per comparison, strain E1 is seen to be more similar to strain NEA12 than to N. lolii strain ST (
The LpTG-2 endophyte strain NEA11 is reported to be a hybrid of N. lolii and E. typhina. Mitochondrial sequence analysis supports the hybridisation of E. typhina with a N. lolii with only the N. lolii mitochondria being retained.
Evidence for the hybrid nuclear genome is seen when nuclear genes are used as a query against contigs from the NEA11 genome assembly (
The panels below show a region of the ‘UDP-N-acetylglucosaminyltransferase’ gene from E. festucae being used as a BLAST(N) query against: E. festucae (E2368) genome contigs; N. lolii (ST) genome contigs; and LpTG-2 (NEA11) genome contigs. This result clearly shows a second variant of this gene in the NEA11 genome that has far more SNPs than the first NEA11 contig hit. This presumably represents the E. typhina copy of this gene that has been retained in the NEA11 genome. It is unlikely that this is a localised duplication in NEA11 as neither E. festucae, nor N. lolii has such a duplication.
The panel below shows the N. lolii peramine gene from GenBank used as a query against NEA11 genome assembly contigs. BLAST(N) alignment of LpTG-2 endophyte strain NEA11 reads against the peramine gene (perA) sequence (GenBank accession number: AB205145). (SEQ ID Nos: 16-21) The presence of SNP in one set of contigs indicates the presence of two copies of the peramine gene sequence in endophyte strain NEA11.
In heterothallic fungi, such as Epichloë spp, strains must be of opposite mating-type for sexual reproduction to proceed. In Epichloë spp, sexual development is regulated by alternative MAT1-1 (comprising MAT1-1-1, MAT1-1-2 and MAT1-1-3) and MAT1-2 (comprising MAT1-2-1) genes at the MAT locus. Although the flanking regions of MAT1-1 and MAT1-2 are homologous, the nucleotide sequences of MAT1-1 and MAT1-2 idiomorphs are highly dissimilar (
The mating-type locus of E. festucae E2368 was contained in contig 5 of the original assembly (University of Kentucky, http://www.genome.ou.edu.fungi.html). This contig was aligned with contigs derived from N. lolii endophyte strain ST. The MAT1-1 mating-type locus genes found in E. festucae (MAT1-1-1, MAT1-1-2, MAT1-1-3) were demonstrated to be absent in the N. lolii consensus sequence (
To assess the mating type of endophyte strain E1, the two possible mating type contigs were compared to E1 contigs. This activity proved that E1 contained the same three (MAT1-1-1, MAT1-1-2, MAT1-1-3) mating-type genes as E. festucae E2368 and is thus of the MAT1-1 mating-type. This is in contrast to the mating type gene of non-N. lolii strain NEA12, which is of the MAT1-2, N. lolii-like, mating-type.
Cluster analysis based on sequence nucleotide diversity shows that endophyte strains E1 and NEA12 cluster with E. festucae strain E2368, with their position in the tree switching between analysis based on the mating-type loci flanking sequence and the NoxR gene respectively, and suggesting that recombination has occurred in these lineages (
The identification of an endophyte strain of the opposite mating-type to previously characterised perennial ryegrass endophyte strains provides a means for molecular breeding of endophytes to deliver favourable traits into the plant endophyte symbiotum through the use of the novel E1 strain endophyte.
Mitochondrial Genome AnalysisThe mitochondrial genome of N. lolii endophyte strain Lp19 was present as a single c.88.7 kb contig. This sequence was used to identify contigs containing mitochondrial DNA sequences in the other N. lolii strains sequenced through BLAST(N)-based sequence similarity. Homology searches identified mitochondrial contigs in the E. festucae strain E2368 assembly the two non-N. lolii genomes and the LpTG-2 genome that were sequenced.
The mitochondrial genome sizes for each of the fungal endophytes sequenced in this study as well as the E. festucae strain E2368 are shown on Table 11. A representative of the Clavicipitaceae, Metarhizium anisopliae (Genbank reference number NC_008068.1), is shown for comparison. The N. lolii mitochondrial genomes are similar in size, ranging from 88,377 bp for G4 to 88,740 bp for AR1. LpTG-2 representative, NEA11 has a mitochondrion genome similar in size to N. lolii. The two non-N. lolii genomes, E1 (63,218 bp) and NEA12 (57,818 bp), have relatively smaller mitochondrial genomes more similar in size to that of E. festucae strain E2368 (69,614 bp) than that of N. lolii.
The multiple mitochondrial DNA sequences were used to generate a mitochondrial genome alignment along with the mitochondrial genome sequence of the Clavicipitaceae fungus Metarhizium anisopliae. The alignment demonstrated that while the different mitochondrial genomes vary in size, the genes are present in the same order and strand sense in all genomes, with differences being due to variable insertions in each strain (
Scoring block presence as 1 and absence as 0, a matrix was created to generate a parsimony tree of the relationships between the mitochondrial genomes (
A similar pattern is observed if a neighbour joining tree is constructed using ClustalW from a DNA alignment of only the 40 blocks of sequence that are shared across all endophyte species (c. 40 kb;
A quantitative PCR (qPCR) method for assaying endophyte biomass in planta has been developed and successfully implemented. The development of a high-throughput PCR-based assay to measure endophyte biomass in planta enables efficient screening of large numbers of plants to study endophyte-ryegrass biomass associations. qPCR-specific primer sets have been designed for the peramine biosynthesis gene (perA). To quantitatively assess in planta endophyte biomass, a standard curve, ranging from 2×102 to 2×106 copies of the target sequence, has been generated from endophyte DNA template (
A proof-of-concept study was conducted using a subset of plants which had been previously analysed using established SSR methodology. The analysis clearly shows a correlation between the quantitative SSR allele scoring and the presence of endophyte in planta (Table 12).
-
- Endophyte E1 is a genetically novel, non-Neotyphodiumlolii endophyte. E1 is representative of an as yet un-named taxon
- This supposition is supported by mitochondrial and nuclear genome sequence analysis
- On the basis of DNA specific content, the predicted alkaloid profile of E1 indicates that the lolitrem B toxins deleterious to animal health are not produced by this endophyte.
- The E1 endophyte does not produce lolitrem B, ergovaline, peramine, lolines or janthitrems in planta.
- Endophyte E1 has the mating-type MAT1-1, the opposite mating-type to that carried by all N. lolii endophytes previously characterised
- Endophyte E1 has a high inoculation success rate in perennial ryegrass as compared to other endophytes
- The identification of an endophyte of the opposite mating-type that is highly compatible and stable in planta provides a means for molecular breeding of endophytes for perennial ryegrass through hyper-inoculation
Hyphal fusion between endophyte strains of the opposite mating-type provides a means for delivery of favourable traits into the host plant via hyper-inoculation. Such strains would include: 1) an endophyte strain that exhibits the favourable characteristics of high inoculation frequency and high compatibility with a wide range of elite perennial ryegrass host germplasm and; 2) an endophyte that exhibits a low inoculation frequency and low compatibility, but has a highly favourable alkaloid toxin profile.
The E1 endophyte strain is genetically novel and is compatible with a wide range of elite germplasm as it can be inoculated with a high degree of success. E1 also is of the opposite mating-type to all of the previously characterised perennial ryegrass endophytes. Molecular breeding may therefore be applied by combining the highly compatible E1 endophyte traits with the favourable toxin profile traits of endophytes such as NEA12.
The process of molecular breeding through vegetative (hyphal) fusion may occur in planta by co-inoculation of two endophyte into the same plant. However, molecular breeding may be more efficiently achieved through vegetative fusion in in vitro culture of endophytes of the opposite mating-type, followed by hyper-inoculation of the resultant endophyte.
The following experimental design is applied for molecular breeding of fungal endophytes
1. Determine vegetative compatibility of known endophytes using established co-culturing methodologies.
2. Generation of auxotrophic mutants (e.g. by gene silencing techniques such as RNAi) for two strains of endophyte, such as E1 and NEA12, exhibiting opposite mating-types.
3. Development of vegetative (hyphal) fusion protocol using a combination of cell well degrading enzymes and PEG-4000.
4. Screen for regenerated endophytes based on survival (indicating complementarity of auxotrophic mutations).
5. Genetic screen using SSR and/or mating-type markers to confirm presence of the hybrid genome in a single nuclear compartment.
6. Inoculation and compatibility/stability assessment of endophytes using established methodologies.
7. Phenotypic assessment of endophyte-host associations using established methodologies.
Colchicine has been widely used for induction of polyploidy in plant species such as perennial ryegrass, as compared to the application to fungi, which has been limited to a few species.
The mitotic spindle inhibitor colchicine is capable of inducing autopolyploidisation, and may be applicable to the production of artificial polyploid endophytes.
Artificial polyploids were generated by colchicine induced chromosome doubling of the endophyte strains ST and NEA12.
NEA12, a janthitrem only producing endophyte, with superior bioprotective properties forms stable associations with a limited range of perennial ryegrass hosts. An artificial polyploid of NEA12 that is non-toxic to mammals, with enhanced bioprotective properties, that is broadly compatible and highly stable is highly desirable to industry.
Generation of Artificial PolyploidsExperiments were conducted to determine the range of colchicine concentrations in which the mycelia of the fungal endophyte N. lolii (strain ST) would grow successfully. Mycelia were grown in colchicine concentrations ranging from 0% to 1% for 21 days and monitored for growth (
Artificial polyploids were generated for endophyte strains ST and NEA12. Endophyte strains ST and NEA12 (n) were grown in 0, 0.1 and 0.2% colchicine and potato dextrose broth for 21 days followed by a 7-10 day recovery period in potato dextrose broth only. Protoplasts were generated from all colchicine concentrations and single colonies isolated (
N. coenophialum strain 13E9301 and LpTG-2 strain NEA11 which are natural heteroploids (3n and 2×n fused respectively) have been utilised as control material for assessment of ploidy changes using flow cytometry. An optimised protocol was established allowing analysis of fungal protoplasts via flow cytometry. A number of colonies have been identified with changes in nuclear DNA content relative to the control samples (
-
- Lolitrem B is the major alkaloid leading to ryegrass staggers in grazing animals.
- A method has been developed to eliminate the production of the detrimental alkaloid lolitrem B, using X-ray mutagenesis induced deletion of genes in the lolitrem B biosynthetic gene cluster, in the ST endophyte.
- Such an endophyte would be advantageous over existing commercial endophytes, as ST is highly stable and broadly compatible.
Ionising radiation is capable of introducing a broad range of mutagenic lesions and has been found to be very effective in many species. Published methods are available to readily detect deletion mutants in targeted plant genes (Li et al, 2002). Experiments have been performed to determine if N. lolii mycelia are amenable to production of mutagenic lesions by ionising radiation, in particular deletion mutations.
Generation of Novel Endophyte Variation Using Ionising RadiationN. lolii strain ST was grown in potato dextrose broth for different periods of time ranging from 2-14 days before exposure to ionising radiation. Radiation from a caesium source was applied to the liquid cultures in doses ranging from 10-30 Gy. Following a recovery period (10-14 days) the radiation dose was repeated. Protoplasts were generated and recovery of individual colonies monitored over a 4-6 week period.
Lolitrem B is the major alkaloid leading to ryegrass staggers in grazing animals. Three genes within the lolitrem B gene cluster, which contains 10 genes all required for synthesis of lolitrem B, were targeted to identify individual N. lolii colonies with deletions (Young et al, 2005). A high throughput PCR screening method was developed to detect for the presence and absence of the three lolitrem B genes (
The strategies implemented for perennial ryegrass endophyte discovery were extended to the resident endophytes of tall fescue (including the FaTG-2 and FaTG-3 taxonomic groups).
A targeted collection of tall fescue germplasm was made from throughout the range of natural growth and domesticated cultivation.
A total of 568 tall fescue accessions obtained from 40 different countries were tested for endophyte incidence using endophyte-specific simple sequence repeat (SSR) genetic markers. Twelve to twenty seeds from each accession were tested for endophyte presence. Total genomic DNA was extracted from two independent seed bulks of 6-10 seeds from each accession and endophytes were detected by PCR amplification with six endophyte-specific SSR markers.
Endophyte was detected in 40% (228/568) of the tall fescue accessions tested. Furthermore, accessions from 23 out of the 40 countries screened were endophyte positive (
A subset of selected endophyte positive samples, were selected for further analysis using 32 endophyte-specific SSR markers. The selected genotypes represent a broad range of known geographical origins, hence representing an effective survey of tall fescue endophyte genotypic variation. A set of 52 reference isolates representing several endophyte species, including the resident endophyte of tall fescue and meadow fescue were also included to the diversity analysis.
The UPGMA phenogram, constructed using average taxonomic distance based on SSR polymorphism across 203 endophyte positive accessions, represented six different known taxa, and two out-grouped clusters (
As defined by the N. coenophialum reference isolates, the N. coenophialum cluster comprised five main sub-clusters, of which the fifth sub-cluster is rather out grouped from the other four (
The genetic variation observed within N. coenophialum was high when comparing it with other taxonomic groups. In the phenogram N. coenophialum strains clustered for the most part according to their geographical origin (
FaTG-2 accessions formed a cluster close, but distinct from isolates of N. lolii (
A set of six endophyte genotypes formed a distinct cluster with putative FaTG-3 reference isolates as defined by the previously-analysed AR endophytes. Furthermore, 13 accessions primarily originating from Morocco (9/13) formed a sub-cluster with putative FaTG-3 isolates and those unidentified accessions, forming a cluster distinct to putative FaTG-3 were named “FaTG-3 like” endophytes (
The identities of selected putative FaTG-2 and FaTG-3 accessions are largely consistent with geographical provenance, as these taxa are known to be characteristic of populations from southern Europe and North Africa.
Two out grouped clusters were also identified and they were named as “out-group I” and “out-group II” (
A number of candidate novel endophytes have been identified.
Metabolic Profiling of Tall Fescue-Endophyte AssociationsRepresentative tall fescue-endophyte associations were selected for metabolic profiling analysis in order to determine the endophyte derived alkaloid profile, in particular, lolitrem B, ergot alkaloids, peramine and lolines.
Analysis of metabolite production was assessed under controlled conditions using a growth chamber. Tall fescue-endophyte associations were each replicated four times by clonal splitting and arranged in a randomised block design in the growth chamber. Plants were maintained in soil for six weeks, with trimming every two weeks to encourage growth. Following 6 weeks growth, pseudostem tissue was harvested and freeze dried prior to performing a metabolite extraction and LCMS analysis. The perennial ryegrass-N. lolii designer association Bronsyn-ST was used as a control as ST is known to produce lolitrem B, ergovaline and peramine. For each of the accessions, the presence and identity of the resident endophyte was confirmed through SSR analysis of the plant material harvested for metabolic profile analysis and endophyte negative samples were removed from further analysis.
The results of the qualitative assessment alkaloid of production for 20 novel tall fescue endophytes are summarised in Table 15. Relative quantitation data for Batch three, comprising 13 endophytes assessed in their endogenous hosts, are shown in
Tissue culture responsive genotypes from selected germplasm material have been generated (Drover, Dovey, Bariane, Barolex). Table 16 shows the host cultivars, and their tissue culture responsive genotype, selected for further study. Each of the selected genotypes has a regeneration frequency greater than 80%
Selected novel endophytes were isolated from tall fescue accessions (Table 17).
A set of ten novel tall fescue endophytes were selected for inoculation based on genetic novelty using SSR-based diversity analysis and the toxin profile based on qualitative metabolic profiling (Table 18). Included in the set was the endophyte AR542 a commercial endophyte in use globally. AR542 was discovered and isolated by AgResearch NZ and is marketed as MaxP™ and MaxQ™
In order to accurately determine the phenotypic effects of different candidate endophytes in the absence of host-specific genetic effects, a system for isogenic inoculation was used. Novel candidate endophytes were individually inoculated into elite tall fescue germplasm as well as the perennial ryegrass host genotype Bronsyn (Bro08). Following inoculation and plantlet regeneration in culture, plants were transferred to soil for three months to allow establishment of endophyte and host-plant associations. After this period, three tillers from each plant were sampled and tested for endophyte presence using SSR-based analysis.
Of the 498 isogenic inoculations tested, 109 (21.9%) could be positively scored with a high degree of confidence. Successful inoculations are listed on Table 19.
Variation in inoculation success according to candidate endophyte identity was observed. Endophyte strain 3 (4.3%), for example, exhibited relatively lower success rates as compared to strain 20 (51.1%), or the commercial endophyte AR542 (44.4%; Table 19) and only formed stable associations with one of the five hosts (Bariane). No successful inoculations were identified for endophyte strain 15. FaTG-2 endophyte, strain 17, is a highly compatible endophyte which obtains a high rate of success of inoculation into tall fescue (Table 19) compared to other endophytes examined, and is comparable to AR542. Out-group 1 endophyte strain 20 exhibits the highest level of compatibility as measured by its ability to be inoculated.
Both tall fescue endophytes inoculated into perennial ryegrass host Bro08, strain NEA13 and strain NEA14, were taken up successfully, establishing that endophyte inoculation across a range of host species is possible.
Neotyphodium endophytes at present are largely unexplored in terms of their production of novel antimicrobials.
While some Epichloë/Neotyphodium endophytes have been shown to inhibit the growth of plant-pathogenic fungi in vitro, the inhibitory substances produced have not been identified.
Endophytes with anti-fungal properties may benefit host plants by preventing pathogenic organisms from colonising them and causing disease. This is of particular interest to the turf grass industry.
A Bioassay to Assess Antifungal Activity of Neotyphodium EndophytesTo determine if endophytes of the species Neotyphodium produce anti-fungal substances in vitro representative species/strains from Neotyphodium were tested for the presence of anti-fungal activity against eight species of fungal plant pathogens.
Three types of inhibition reactions were observed. In the first reaction, pathogenic fungal growth was unaffected. In the second, growth of the pathogenic fungi was initially unaffected, but growth ceased when the colony margin approached a “critical” distance from the central endophyte colony. In the third stronger reaction type, the overall growth of the colony of the pathogenic fungi was reduced. Examples of inhibition reactions are shown in
Variation was observed within and between endophyte taxa. Non-N. lolii strain NEA12 exhibits the strongest and most broad spectrum antifungal activity. Variation was also observed among genetically distinct strains of N. lolii. Within N. lolii, strains with strongest to weakest effects were ST>AR1>NEA3>NEA10. ST exhibited the broadest spectrum of antifungal activity, inhibiting the growth of 7/8 fungi strains tested. The bioassay results showed that endophytes in vitro exhibit variation in anti-fungal activity that does not correlate with known toxin production (specifically, lolitrem B, ergovaline and peramine). For example NEA12 does not produce lolitrem B, ergovaline and peramine and has strong antifungal activity and ST does produce lolitrem B, ergovaline and peramine and also has strong antifungal activity.
Mass spectrometry was used to determine the relationship between antifungal activity and metabolite expression.
Endophyte strains representing the full spectrum of antifungal activity were selected for analysis in order to identify those alkaloids that may be associated with antifungal activity (
Endophyte strains were grown both in the presence and absence of the pathogenic fungi Rhizoctonia cerealis (
Following extraction, a validation assay was done to ensure that the alkaloids associated with antifungal activity had been appropriately extracted (
Perennial ryegrass cultivars inoculated with the NEA12 endophyte were analysed using LCMS. The toxins peramine, ergovaline and lolitrem B were not detected in the extract. The AR37 metabolite 11,12-epoxy janthitrem G was detected and its structure assigned based on retention time and MS analysis of an extract of the AR37 inoculated perennial ryegrass.
Metabolic Profiling of Endophyte NEA12 in Perennial Ryegrass.Perennial ryegrass cultivars inoculated with different endophytes were analysed for peramine (1), ergovaline (2), lolitrem B (3) and the AR37 isolated metabolites janthitrem l (4) (11,12-epoxy janthitrem G (janthitrem G (5)) by LCMS. Janthitrem G is an isomer of the previously described janthitrem F (6) and its structure was determined by NMR in the original patent describing AR37 (Latch et al, 2000; structures shown in
Standards were analysed to provide reference for the perennial ryegrass analyses. The lolitrem B standard had deteriorated significantly but a peak matching the expected m/z and approximate retention time could be found (
Data for AR37 inoculated endophyte and NEA12-inoculated ryegrass gave comparable results. Neither contained detectable levels of peramine, ergovaline or lolitrem B. Both contained 11,12-epoxy-janthitrem G (4) (
Analysis of NEA12 was carried out in a number of perennial ryegrass cultivars. It was present to a greater or lesser extent in the majority of those examined (Table 21). No attempt was made to quantitate the amount found. A standard toxic (ST) endophyte was analysed in the same perennial ryegrass cultivars. The ST endophyte produced peramine and ergovaline but not janthitrems (Table 21). The toxin profiles for ST and NEA12 are shown in
The NEA12 endophyte appears to have the same alkaloid profile as AR37 and is distinctly different from the ST endophyte.
EXAMPLE 10—TALL FESCUE ENDOPHYTE DISCOVERYThe objectives of this work on discovery and characterization of endophytes in tall fescue (Lolium arundinaceum) were:
1. Identification and characterisation of novel tall fescue endophytes for evaluation in germplasm.
2. Development and evaluation of optimised associations between novel endophytes and elite germplasm.
The endophyte discovery was based on screening 568 accessions to identify endophyte positive plants followed by genotyping 210 endophytes to identify novel endophytes in tall fescue.
The characterisation in planta of novel endophytes from tall fescue was based on the following steps:
-
- Meristem cultures for tall fescue cultivars were established for isogenic host panel
- Endogenous metabolic profiles were determined for 48 samples
- Isolation of 38 endophytes was undertaken
- Inoculation of 15-20 endophytes into isogenic host panel was undertaken
- Isogenic host-endophyte associations were characterised
Genotypic Analysis of Endophyte Content in Accessions from a Targeted Fescue Germplasm Collection
Initially, 472 accessions from 30 countries were tested for endophyte incidence; with 2 replicates of 6-10 seeds in each bulk per accession used in the analysis and endophyte incidence assessed with 6 SSRs.
New accessions were included in the analysis from the under-represented geographic origins; with a total of 568 accessions from 40 countries tested for endophyte incidence.
Genotypic analysis of endophyte content in accessions from a targeted fescue germplasm collection is shown in Table 22. 233 endophyte positive accessions (41%) were detected. The geographical origins are represented in the endophyte incidence assessment.
A genetic diversity analysis of tall fescue endophytes is shown in
Diversity of host and endophyte is shown in
Selection of fescue-endophyte combinations for metabolic profiling, endophyte isolation and isogenic inoculation is shown in
Selection of fescue-endophyte combinations for metabolic profiling, endophyte isolation and isogenic inoculation is shown in
The desired toxin profile of tall fescue endophytes is shown in
The experimental design used for semi-quantitative metabolic profile analysis of tall fescue-endophyte associations for the detection of alkaloid production in the endogenous host background is described below.
A metabolic profile analysis for detection of ergovaline and peramine is shown in
Endophytes selected for semi-quantitative analysis of metabolites are shown in
A metabolic analysis of tall fescue-endophyte associations for the detection of alkaloid production including loline, loline formate, peramine, ergovaline and lolitrem B in the endogenous host background is shown in
Further metabolic analysis of the fescue endophytes is shown in
In addition to the metabolic analysis of tall fescue-endophyte associations grown under standard conditions, for the detection of alkaloid production conferred by the endopohytes in the endogenous host background (
-
- Harvest (control)→freeze dry→50 mg pseudostem material→80% methanol extraction→LCMS analysis
- Recovery and water stress
- Second harvest (stress)→freeze dry→SSR confirm all of the plant material again.
This was performed in a controlled (growth chamber) environment simulating summer conditions, with light watering as required. Nine copies per accession were planted in general potting mix. A Randomized Complete Block with subsampling was used.
A total of 36 fescue endophytes have been isolated from a range of fescue accessions from different geographic origin as described in Table 24, and found to belong to different taxa as follows: 19 of them being N. coenophialum; 5 of them being FaTG-2; 3 of them being Outgroup; 3 of them being FaTG-3; 3 of them being FaTG-3 like; and 3 of them being N. uncinatum
Table 25 shows selected tall fescue and perennial ryegrass cultivars used to identify representative plant genotypes included in the diverse host panel for in planta inoculation of fescue endophytes. All the selected plant genotypes have a high regeneration frequency of >80%.
Isolated fungal endophytes from endophyte-containing fescue accessions selected for in planta isogenic inoculation into the diverse host panel are shown in
Results from the SSR genotyping indicating the allele number and sizes for different SSR markers for the different fescue endophyte strains are shown in Table 26.
Results from the in planta isogenic inoculation into the diverse host panel of selected isolated fungal endophytes from endophyte-containing fescue accessions are shown in Table 27. Data on number of inoculations tested, number of successful inoculations and % of successful inoculations are provided in Table 6 to illustrate the inoculation ability of tall fescue endophytes in tall fescue and perennial ryegrass hosts.
Following in planta isogenic inoculation with a range of selected isolated endophytes from fescue accessions, the endophyte vegetative stability of these endophytes in the different tall fescue and perennial host genotypes (i.e. BRO 08, BARI 27, DOV 24) was assessed, showing that:
-
- Several tall fescue endophytes (e.g. NEA17, NEA18, NEA19) were stable in perennial ryegrass (BRO08).
- BAR127 formed stable associations with all endophytes except for NEA15.
- NEA15 failed to form stable associations with any of host genotypes tested.
- DOV24 formed few stable associations.
The stability of these associations of novel tall fescue endophytes inoculated in different tall fescue and perennial ryegrass genotypes from the diverse host panel was assessed 12 months post-inoculation. Corresponding results are shown in Table 28.
The range of novel fescue endophytes selected for in planta isogenic inoculation is shown in
Table 29 shows additional novel tall fescue endophytes (e.g. NEA20, NEA21, NEA22, etc.) selected for in planta isogenic inoculations in tall fescue genotypes (i.e. BARI 27, JESS 01 and QUAN 17) from the diverse host panel, based on the following selection criteria:
-
- 1. Produce little or no ergovaline
- 2. Produce no lolitrem B
- 3. Produce lolines and/or peramine
Metabolic profiling of endophyte-tall fescue associations established following in planta isogenic inoculations of novel tall fescue endophytes in tall fescue genotypes from the diverse host panel is shown in
-
- Compare semi-quantitative alkaloid profiles of selected endophytes across different isogenic hosts
- Compare semi-quantitative alkaloid profiles for diverse endophytes in an isogenic host
- Compare semi-quantitative alkaloid profiles of tall fescue and perennial ryegrass endophytes in the perennial ryegrass genotype Bro08
Table 30 shows metabolic profiling of endophyte-tall fescue associations established following in planta isogenic inoculations of novel tall fescue endophytes in tall fescue genotypes from the diverse host panel. Confirmed endophyte positive (E+) plants were split to 5 replicates and regularly trimmed to promote tillering. Four months later E+ plants were re-potted in 12 replicates. One month later E+ plants were re-potted if less than 9 positive copies were available at the time. Endophyte status was tested using SSR markers after each re-potting.
A range of endophyte-tall fescue associations established following in planta isogenic inoculations of novel tall fescue endophytes in tall fescue genotypes from the diverse host panel were selected for metabolic profiling (Table 30). In total, 29 isogenic host-endophyte associations were subject to LCMS analysis, following the experimental design described below:
Experimental Design
-
- Trim and re-pot plants
- 16 h Light, 30° C.; 18 h Dark, 20° C.
- Harvest (control)→freeze dry→50 mg pseudostem material→80% methanol extraction→LCMS analysis
- Recovery and water stress
- Second harvest (stressed)→freeze dry→50 mg pseudostem material→80% methanol extraction→LCMS analysis.
This was performed in a controlled (growth chamber) environment simulating summer conditions, with light watering as required. Nine copies per accession were planted in general potting mix. A Randomized Complete Block with subsampling was used.
EXAMPLE 16—BIO-PROTECTIVE PROPERTIES OF FESCUE ENDOPHYTESThree fungal pathogens (i.e. Colletrotrichum graminicola, Drechslera brizae and Rhizoctonia cerealis)—causing a range of fungal diseases and infecting a range of different plant hosts—were included in antifungal bioassays used to analyse the potential anti-fungal activities of isolated fescue endophytes.
A range of novel tall fescue endophtyes were subjected to genome survey sequencing (GSS).
Table 37 shows results from the assessment of alkaloid biosynthetic gene presence/absence for different endophytes by mapping genome survey sequence reads corresponding to the different alkaloid biosynthetic genes/gene clusters as well as corresponding alkaloid profile observed for corresponding tall fescue-endophyte associations.
Table 38 shows novel fescue endophytes (NEA16, NEA18, NEA19, NEA20, NEA21 and NEA23) with favourable toxin profiles.
A genotypic analysis of the novel fescue endophytes NEA23 and NEA21 is shown in
The objective of this work was to create novel variants of the perennial ryegrass endophyte, Neotyphodium lolii, through induced polyploidisation and mutagenesis, with desirable properties such as enhanced bioactivities (e.g. antifungal acitivity), and/or altered plant colonization ability and stability of grass host-endophyte variant associations (e.g. altered in vitro growth), and/or altered growth performance (e.g. enhanced plant vigour, enhanced drought tolerance, enhanced water use efficiency) of corresponding grass host-endophyte variant associations. These grass host-endophyte variant associations are referred to as novel ‘designer’ grass-endophyte associations.
Experimental Strategies for the Generation and Characterisation of Novel Designer Neotyphodium Endophyte Variant Strains Through MutagenesisThe experimental activities thus included:
1. Establishment of phenotypic screens for novel ‘designer’ grass-endophyte associations such as:
-
- Enhanced biotic stress tolerance
- Enhanced drought tolerance and enhanced water use efficiency
- Enhanced plant vigour
2. Targeted generation (i.e. polyploidisation and X-ray mutagenesis) and characterisation (i.e. antifungal bioassays, in vitro growth rate, genome survey sequencing [GSS]) of novel ‘designer’ endophytes
3. Breeding of ‘designer’ grass-endophyte associations - Delivery of ‘designer’ endophytes into grass (e.g. perennial ryegrass) germplasm development process.
Assessment of enhanced biotic stress tolerance using NEA12 is shown in
Assessment of enhanced drought tolerance and enhanced water use efficiency is shown in
This involved creation of novel variation in Neotyphodium endophytes without the use of transgenic technology. Colchicine has been widely and successfully used for chromosome doubling in plants, e.g. perennial ryegrass. It inhibits chromosome segregation during mitosis inducing autopolyploidisation (chromosome doubling; see
The experimental work flow for chromosome doubling is shown in
Flow cytometry calibrations to assess DNA content in Neotyphodium endophytes are shown in
Flow cytometry analysis of NEA12dh strains is shown in
1. ST endophyte strain is highly stable, broadly compatible and produces lolitrems, peramine and ergovaline. 2. NEA12 endophyte strain produces janthitrem only. 3. AR1 produces peramine only.
Analysis of growth rate of NEA12dh Neotyphodium variant endophyte strains in in vitro culture after 8 weeks is shown in
NEA12dh17 grows significantly faster (p<0.01**)
NEA12dh4 grows significantly slower (p<0.05*)
Analysis of growth rate of NEA12dh Neotyphodium variant endophyte strains in in vitro culture over 5 weeks is shown in
NEA12dh17 grows significantly faster (p<0.01**)
NEA12dh15 grows significantly slower (p<0.01**)
A list of fungal pathogens (causing a range of fungal diseases and infecting a range of different plant hosts) that were included in antifungal bioassays used to analyse NEA12dh Neotyphodium variant endophyte strains to assess their spectrum of antifungal activities is shown in Table 40.
Antifungal bioassays of NEA12dh Neotyphodium variant endophyte strains are shown in
NEA12dh Neotyphodium variant endophyte strains with enhanced antifungal activity, showing faster in vitro growth rate and higher DNA content were subjected to genome survey sequencing (GSS). Sequence data was generated for 10 NEA12dh strains and control NEA12 strain (highlighted in blue on Table 41).
Genome survey sequencing (GSS) data obtained for NEA12dh Neotyphodium variant endophyte strains derived from colchicine treated NEA12 control strain (highlighted in blue on Table 41) were analysed as follows:
-
- De-novo assembly of the GSS data from NEA12 control strain—to act as a reference genome sequence for the analysis of the NEA12dh Neotyphodium variant endophyte strains
- Map the GSS data sequence reads from the NEA12dh Neotyphodium variant endophyte strains to the NEA12 reference genome sequence
- Identify potentially duplicated regions, i.e. regions with higher than expected sequence coverage
- Identify gene sequences that may have been duplicated
Analysis of GSS read depth of NEA12dh Neotyphodium variant endophyte strains is shown in
Analysis of GSS sequence assemblies for the NEA12dh Neotyphodium variant endophyte strains and the control NEA12 strain is shown in Table 42.
Independent de novo sequence assemblies were performed using parameters identical to those used in assembling the genome sequence for the control NEA12 endophyte strain. Differences in sequence assembly statistics may indicate genomic differences between strains. GSS data obtained for the NEA12dh Neotyphodium variant endophyte strains and used in the sequence assemblies reveal fewer bases incorporated into the sequence assembly and produce more sequence contigs. Increased numbers of smaller sequence contigs may be caused by transposon movement/replication.
Analysis of sequence reads mapping to the NEA12 genome sequence assembly is shown in
Sequence read depth changes were analysed in NEA12dh Neotyphodium variant endophyte strains compared with the control NEA12 strain. Whilst no large partial genome sequence duplication events were detected, the occurrence of full genome duplication events in the NEA12dh Neotyphodium variant endophyte strains cannot be excluded based on the GSS sequence analysis.
De novo sequence assemblies were independently performed on GSS data obtained from the NEA12dh Neotyphodium variant endophyte strains. Differences in sequence assembly statistics indicate that genomic changes were caused by the colchicine-treatment in the NEA12dh Neotyphodium variant endophyte strains. The number of sequence reads from NEA12dh Neotyphodium variant endophyte strains mapping to the NEA12 reference genome sequence varies between strains. All GSS data analyses performed on the NEA12dh Neotyphodium variant endophyte strains indicate genomic differences.
In summary, the following novel designer endophytes were generated by colchicine treatment of NEA12 endophytes:
-
- Four NEA12dh Neotyphodium variant endophyte strains (dh5, dh6, dh13 and dh14) with enhanced bioprotective properties (i.e. antifungal bioactivities);
- One NEA12dh Neotyphodium variant endophyte strain (dh17) with higher in vitro growth rate than control NEA12 strain (i.e. potentially with enhanced stability/host colonization ability);
- Ten NEA12dh Neotyphodium variant endophyte strains (including dh5, dh6, dh13, dh14 and dh17) and control NEA12 strain subjected to genome survey sequencing; and
- Five NEA12dh Neotyphodium variant endophyte strains (including dh5, dh13 and dh17) selected and subjected to isogenic inoculation in planta.
The following NEA12dh Neotyphodium variant endophyte strains and control NEA12 strain were used for in planta isogenic inoculation in perennial ryegrass:
-
- NEA12
- NEA12dh5 showing higher antifungal activity than control NEA12
- NEA12dh13 showing higher antifungal activity than control NEA12
- NEA12dh4 showing slower in vitro growth rate than control NEA12
- NEA12dh15 showing slower in vitro growth rate than control NEA12
- NEA12dh17 showing faster in vitro growth rate than control NEA12
The generation of designer Neotyphodium endophytes genotypes by X-ray mutagenesis offers the opportunity to create novel endophyte variant strains with enhanced properties, such as enhanced stability in grass hosts, broader host compatibility as well as improved toxin profiles e.g. following elimination of the production of the detrimental alkaloid lolitrem B in the highly stable and broadly compatible ST endophyte.
Such an novel designer endophyte would be advantageous over existing commercial endophytes, such as AR1 and AR37, as it would be highly stable and broadly compatible and with optimal toxin profile.
In a preliminary primary screen >5,000 colonies of X-ray irradiated N. lolii—established as an initial resource of novel variation of N. lolii endoophytes induced through X-ray mutagenesis and representing a mutagenised N. lolii endophyte strain collection—of were screened by multiplex PCR analysis for the presence of targeted Ltm genes leading to a preliminary identification of ˜140 putative lolitrem B gene cluster PCR-negative colonies (˜2.5% of 5,000 colonies screened). In a secondary screen high quality DNA was extracted (140 liquid cultures) and PCR analysis conducted. This identified 2 putative deletion mutants for one of the lolitrem B genes (Itm J).
EXAMPLE 27—ANTIFUNGAL BIOASSAYS OF DESIGNER X-RAY IRRADIATED N. BORN VARIANT STRAINSThere were eight X-ray irradiated N. lolii variant strains (i.e. X-ray mutagenesis derived variant strains 1-35, 4-7, 7-22, 7-47, 123-20, 124-6, 139-6, 144-16 and 145-15) and one control N. lolii strain (i.e. ST endophyte strain).
Five fungal pathogens (causing a range of fungal diseases and infecting a range of different plant hosts) were included in antifungal bioassays used to analyse the X-ray irradiated N. lolii variant strains, as follows:
-
- Bipolaris portulacae
- Colletotrichum graminicola
- Drechslera brizae
- Phoma sorghina
- Rhizoctonia cerealis
No significant difference in antifungal activities of X-ray irradiated N. lolii variant strains tested was observed compared to the spectrum of antifungal activities observed for the control ST endophyte strain.
EXAMPLE 28—IN VITRO GROWTH OF DESIGNER X-RAY IRRADIATED N. LOLII VARIANT STRAINSResults from the analysis of in vitro growth rate of designer X-ray irradiated N. lolii variant strains are shown in
Eight X-ray irradiated N. lolii ST variant strains and corresponding control ST strain were subjected to genome survey sequencing (GSS), leading to 46-fold to 79-fold genome sequence coverage for the different strains as shown in Table 45.
Results from the analysis to detect genome sequence variation in X-ray irradiated N. lolii variant strains are shown in
Results on sequence analysis for Ltm gene clusters are shown in
Table 46 shows examples of some of these genome sequence deletions detected in X-ray irradiated N. lolii variant deletion mutant strains.
The X-ray irradiated N. lolii variant deletion mutant strain #7_47, which was generated following two X-irradiation treatments at 10 Gy dose (10Gy*2) of N. lolii ST endophyte, had the greatest number of large deletions.
EXAMPLE 32—ANNOTATION OF DELETED SEQUENCES IN THE GENOMES OF X-RAY IRRADIATED N. LOLII VARIANT DELETION MUTANT STRAINS X-Ray Irradiated N. Lolii Variant Mutant Strain 1_35:For the X-ray irradiated N. lolii variant mutant strain 1_35 the following deleted sequences in ST454Contig00831 contig with a ˜4,400-8,000 bp length was detected, with this genome sequence region containing the following two predicted genes:
ST454contig00831_AUGUSTUS_gene_3318:6018 (847 letters)
1) ref |XP_386347.1| hypothetical protein FG06171.1 [Gibberella 660×0.0 gb|EAW12630.1| DUF500 domain protein [Aspergillus NRRL 1]; 253×9e-66, and ST454contig00831_AUGUSTUS_gene_3958:4728 (183 letters); and
2) gb|EAW13545.1| 2,3-cyclic-nucleotide 2-phosphodiesterase [Aspergillus 32×2.4
X-Ray Irradiated N. lolii Variant Mutant Strain 7_47:
For the X-ray irradiated N. lolii variant mutant strain 7_47 the following deleted sequences in ST454Contig01082, ST454Contig01131 and ST454Contig02985, with these genome sequence regions containing no predicted genes:
Given that ST endophyte has approximately 443.5 genes per Mb, using 10Gy*2 treatment, the expected rate of SNP/INDEL occurrence is 0.33 per gene in the genome.
SummaryX-ray irradiated N. lolii variant deletion mutant strains were analysed for many types of genome sequence variation i.e. deletions, SNPs, INDELs, inversions and translocations. SNPs, INDELs, deletions and duplications were identified in the genome survey sequences of X-ray irradiated N. lolii variant deletion mutant strains. There was an apparent peak in number of SNPs and INDELs in X-ray irradiated N. lolii variant deletion mutant strains recovered from administering 10Gy*2 X-ray irradiation treatment to N. lolii ST endophyte. The X-ray irradiated N. lolii variant deletion mutant strain 7_47 had 3 large deletions. It was demonstrated that this mutagenesis method based on X-ray irradiation can be used to create novel designer Neotyphodium endophyte strains, and enabled:
-
- 5,000 X-ray irradiated N. lolii variant endophyte strains derived from X-ray irradiation of ST N. lolii endophyte were screened;
- 140 putative X-ray irradiated N. lolii variant endophyte mutant strains were identified;
- 9 X-ray irradiated N. lolii variant endophyte mutant strains were subjected to antifungal bioassays;
- 9 X-ray X-ray irradiated N. lolii variant endophyte mutant strains were subjected to in vitro growth assays;
- 9 X-ray irradiated N. lolii variant endophyte mutant strains were subjected to genome survey sequencing;
- 2 X-ray irradiated N. lolii variant endophyte mutant strains with gene deletions (1_35 and 7_47) were identified; and
- 3 X-ray irradiated N. lolii variant endophyte mutant strains with gene duplications (124_6, 139_6 and 145_15) were identified.
Results from metabolic profiling of colchicine treatment derived NEA12dh endophyte variant strains is shown in
Results from metabolic profiling of X-ray irradiation treatment derived N. lolii ST endophyte variant strains is shown in
The following endophytes were grown on PDB for 3 weeks:
-
- Control N. lolii ST endophyte strain
- X-ray irradiation treatment derived N. lolii ST endophyte variant strain 4-7
- X-ray irradiation treatment derived N. lolii ST endophyte variant strain 139-6
- X-ray irradiation treatment derived N. lolii ST endophyte variant strain 144-16
- X-ray irradiation treatment derived N. lolii ST endophyte variant strain 145-15
and subjected to metabolic profiling using LCMS on corresponding - 1. Liquid filtrate
- 2. Mycelial extract
The X-ray irradiation treatment derived N. lolii ST endophyte variant strains could be readily distinguished from control N. lolii ST strain using mycelia extracts or filtrates alone.
It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.
REFERENCES
- Bouton, J. H., G. C. M. Latch, N. S. Hill, C. S. Hoveland, M. A. McCann, R. H. Watson, J. A. Parish, L. L. Hawkins and F. N. Thompson (2002) Agronomy Journal 94(3): 567 574.
- Latch, G. C. M, Christensen, M. J, Tapper, B. A, Easton, H. S, Hume, D. E, Fletcher, L. R. (2000) U.S. Pat. No. 6,111,170 and references therein.
- Li, X and Zhang, Y., (2002) Comparative and Functional Genomics 3: 158-160.
- Tapper, B. A, Cooper, B. M, Easton, H. S, Fletcher, L. R, Hume, D. E, Lane, G. A, Latch, G. C. M, Pennell, C. G. L, Popay, A. J, Christensen, M. J. (2004) International Patent Application No. WO 2004/106487 and references therein.
- Van Zijll de Jong E, Guthridge K M, Spangenberg G C, Forster J W (2003) Genome 46 (2): 277-290
- Young, C. A., Bryant, M. K., Christensen, M. J., Tapper, B. A., Bryan, G. T., Scott, B. (2005) Molecular Genetics and Genomics, 274: 13-39.
Claims
1-32. (canceled)
33. A plant, seed, or part thereof,
- wherein the plant is a tall fescue or perennial ryegrass plant,
- wherein the plant, seed, or part thereof is associated with a fungal endophyte isolated from one of tall fescue and perennial ryegrass, said endophyte being selected from the group consisting National Measurement Institute Accession Nos. V10/000002, V10/000003, V10/00004, V10/00001, V10/030284, V10/030285, V12/001413, V12/001414, V12/001415, V12/001416, V12/001417, V12/001418 and V12/001419, and
- wherein the plant, seed or part thereof is associated with a fungal endophyte isolated from a different type of plant to form an association that does not occur in nature.
34. The plant, seed, or part thereof according to claim 33, wherein said plant is a tall fescue, the plant, seed, or part thereof is associated with an endophyte selected from the group consisting of National Measurement Institute Accession Nos. V10/000002, V10/000003, and V10/00004.
35. The plant, seed, or part thereof according to claim 33, wherein said plant is a perennial ryegrass plant, the plant, seed, or part thereof and is associated with an endophyte selected from the group consisting of National Measurement Institute Accession Nos. V10/00001, V10/030284, V10/030285, V12/001413, V12/001414, V12/001415, V12/001416, V12/001417, V12/001418 and V12/001419.
Type: Application
Filed: Nov 23, 2016
Publication Date: May 4, 2017
Applicant: Agriculture Victoria Services PTY LTD (Attwood)
Inventors: German Spangenberg (Bundoora), Kathryn Michaela Guthridge (Hadfield), John White Forster (Diamond Creek), Timothy Ivor Sawbridge (Coburg), Emma Jane Isobel Ludlow (Viewbank), Jatinder Kaur (Taylors Hill), Simone Jane Rochfort (Reservoir), Maia Andrea Rabinovich (Buenos Aires), Piyumi Ekanayake (Bundoora)
Application Number: 15/359,993
