ACYL-ACP THIOESTERASES AND MUTANTS THEREOF
Novel plant acyl-ACP thioesterase genes of the FatB and FatA classes and proteins encoded by these genes are disclosed. The genes are useful for constructing recombinant host cells having altered fatty acid profiles. Expression of the novel and/or mutated FATB and FATA genes is demonstrated in oleaginous microalga host cells. Furthermore, a method for producing an oil elevated in one or more of C12:0, C14:0, C16:0, C18:0 and/or C18:1 fatty acids includes transforming a cell with novel and/or mutated FATB and/or FATA genes, e.g., having an N-terminal deletion. The cells produce triglycerides with altered and useful fatty acid profiles.
This application is a continuation of U.S. application Ser. No. 14/858,527, filed on Sep. 18, 2015, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62/052,440, filed on Sep. 18, 2014, and U.S. Provisional Application No. 62/075,168, filed on Nov. 4, 2014, all of which are hereby incorporated herein in their entireties.
SEQUENCE LISTINGThis instant application contains a Sequence Listing which has been submitted electronically in ASCCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Nov. 20, 2015, is named SOLAP0281412A01_SL.txt and is 163,325 bytes in size.
BackgroundCertain organisms including plants and some microalgae use a type II fatty acid biosynthetic pathway, characterized by the use of discrete, monofunctional enzymes for fatty acid synthesis. In contrast, mammals and fungi use a single, large, multifunctional protein.
Type II fatty acid biosynthesis typically involves extension of a growing acyl-ACP (acyl-carrier protein) chain by two carbon units followed by cleavage by an acyl-ACP thioesterase. In plants, two main classes of acyl-ACP thioesterases have been identified: (i) those encoded by genes of the FatA class, which tend to hydrolyze oleoyl-ACP into oleate (an 18:1 fatty acid) and ACP, and (ii) those encoded by genes of the FatB class, which liberate C8-C16 fatty acids from corresponding acyl-ACP molecules.
Different FatB genes from various plants have specificities for different acyl chain lengths. As a result, different gene products will produce different fatty acid profiles in plant seeds. See, U.S. Pat. Nos. 5,850,022; 5,723,761; 5,639,790; 5,807,893; 5,455,167; 5,654,495; 5,512,482;5,298,421;5,667,997; and 5,344,771; 5,304,481. Recently, FatB genes have been cloned into oleaginous microalgae to produce triglycerides with altered fatty acid profiles. See, WO2010/063032, WO2011/150411, WO2012/106560, and WO2013/158938.
SUMMARYAccording to an embodiment, there is a nucleic acid construct comprising a polynucleotide sequence encoding a heterologous regulatory element and a FatB acyl-ACP thioesterase gene operable to produce an altered fatty acid profile in an oil produced by a cell expressing the nucleic acid construct. The FatB gene expresses a protein having an amino acid sequence having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% identity to any of SEQ ID NOS: 1-18 or an amino acid sequence encoding a plastid targeting peptide fused upstream of any of SEQ ID NOS: 10-18.
Optionally, the acyl-ACP thioesterase coding sequence of the nucleic acid construct comprises at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% identity to any of SEQ ID NOS: 19-36 or any equivalent sequences by virtue of the degeneracy of the genetic code. In varying embodiments, the protein further comprises an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A).
In varying embodiments, the construct can have a plastid targeting peptide with at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% identity to SEQ ID NO: 37. In varying embodiments, the construct can have a plastid targeting peptide with at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% identity to SEQ ID NO: 40.
The FatB gene can express an active acyl-ACP-thioesterase protein having an amino acid sequence having:
(a) greater than 94.5, 94.6, 94.7, 94.8, 94.9, 95, or 95.1% identity to SEQ ID NO: 5;
(b) greater than 95.7, 95.8, 95.9, 96, 96.1 or 96.2% identity to SEQ ID NO: 14;
(c) greater than 95.4, 95.5, 95.6, 95.7, 95.8, 95.9, or 96% identity to SEQ ID NO: 3;
(d) greater than 94.5, 94.6, 94.7, 94.8, 94.9, 95, or 95.1% identity to SEQ ID NO: 12;
(e) greater than 94.8, 94.9, 95, 95.1, 95.2, 95.3, or 95.4% identity to SEQ ID NO: 1;
(f) greater than 95.9, 96.0, 96.1, 96.2, 96.3 or 96.4% identity to SEQ ID NO: 10;
(g) greater than 94.5, 94.6, 94.7, 94.8, 94.9, 95, or 95.1% identity to SEQ ID NO: 6;
(h) greater than 95.7, 95.8, 95.9, 96, 96.1 or 96.2% identity to SEQ ID NO: 15;
(i) greater than 94.5, 94.6, 94.7, 94.8, 94.9, 95, or 95.1% identity to SEQ ID NO: 4;
(j) greater than 95.7, 95.8, 95.9, 96, 96.1 or 96.2% identity to SEQ ID NO: 13;
(k) greater than 94.3, 94.4, 94.5, 94.6, 94.7, 94.8, or 94.9% identity to SEQ ID NO: 2;
(l) greater than 94.9, 95, 95.1, 95.2, 95.3, 95.4, or 95.5% identity to SEQ ID NO: 11;
(m) greater than 93.5, 93.6, 93.7, 93.8, 93.9, 94.0, or 94.1% identity to SEQ ID NO: 7;
(n) greater than 92.8, 92.9, 93.0, 93.1, 93.2, 93.3, or 93.4% identity to SEQ ID NO: 16;
(o) greater than 86.5, 86.6, 86.7, 86.8, 86.9, 87, or 87.1% identity to SEQ ID NO: 8;
(p) greater than 85.1, 85.2, 85.3, 85.4, 85.5, 85.6 or 85.7% identity to SEQ ID NO: 17;
(q) greater than 88, 88.1, 88.2, 88.3, 88.4, 88.5, or 88.6% identity to SEQ ID NO: 9; or
(r) greater than 87.6, 87.7, 87.8, 87.9, 88, 88.1, or 88.2% identity to SEQ ID NO: 18.
In another embodiment, a host cell is capable of expressing the nucleic acid construct so as to produce a triglyceride oil having an altered composition relative to a control cell without the construct. Optionally the oil has an increase in C8-C12 fatty acids.
The host cell can be selected, without limitation, from a plant cell, a microbial cell, and a microalgal cell.
In a third embodiment, a recombinant host cell produces an altered fatty acid profile, using a method comprising transforming the host cell with the nucleic acid construct. The host cell can, without limitation, be a microbial cell, a plant cell, or a microalgal cell. In varying embodiments, the host cell expresses a nucleic acid encoding a protein having an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A), and produces at least 2-fold the amount of C18:0 and/or C18:1 fatty acids compared to a host cell that expresses the wild-type protein.
In a fourth embodiment, a method produces an oil or oil-derived product, by cultivating a host cell as mentioned above and extracting the oil produced. Optionally, the cultivation is by heterotrophic growth on sugar. Optionally, the method also includes producing a fatty acid, fuel, chemical, food, or other oil-derived product from the oil. Optionally, an oil is produced having a fatty acid profile comprising at least 20% C8, C10, C12, C14, C16 or C18 (e.g., C18:0 and/or C18:1) fatty acids. Where the oil is produced by a microalgae, the oil can have a microalgal sterol profile and optionally lack C24-alpha sterols. The oil can be used to produce an oil-derived product, optionally a fatty acid, fuel, chemical, food, or other oil-derived product from the oil produced by the above method.
In a fifth embodiment, there is a method for producing an oil. The method includes providing a plastidic, oleaginous cell, optionally a microbial cell expressing a functional, acyl-ACP thioesterase gene encoded by a FATB gene having a deletion mutation in a region corresponding to the region coding for amino acids 66-98 of SEQ ID NO: 8. cultivating the cell to produce a cell-oil, and isolating the cell-oil from the cell. The cell-oil can be enriched in C12 due to the deletion. The FATB gene can encode a protein with at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NOS: 40 to 43. The FATB gene can have least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NOS: 44 or 45 or equivalent sequence by virtue of the degeneracy of the genetic code.
In a sixth embodiment, a cDNA, gene, expression cassette or host cell comprising a polynucleotide encoding a FATB protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to any of SEQ ID NOS: 40 to 43.
In a seventh embodiment, a cDNA, gene, expression cassette or host cell comprises a polynucleotide having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NOS 44 or 45, or equivalent sequence by virtue of the degeneracy of the genetic code.
In an eight embodiment, a method of genetically engineering a cell includes expressing in the cell, a polynucleotide that encodes a protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to any of SEQ ID NOS: 40 to 43; or has at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NOS: 47 or 48, or equivalent sequence by virtue of the degeneracy of the genetic code.
In a further aspect, provided is a cDNA, gene, expression cassette or host cell comprising a polynucleotide encoding a FATA protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61 and wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A). In a further aspect, provided is a cDNA, gene, expression cassette or host cell comprising a polynucleotide encoding a FATA protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61, or equivalent sequence by virtue of the degeneracy of the genetic code and wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A). In a further aspect, provided is a method of genetically engineering a cell comprising expressing in the cell, a polynucleotide that (a) encodes a protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61, wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A).
In a further aspect, provided is a host cell capable of expressing the nucleic acid construct encoding a FATA protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61 and wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A) so as to produce a triglyceride oil having an altered composition relative to a control cell without the construct, the oil optionally having an increase in C18 fatty acids, including C18:0 and C18:1 fatty acids. In varying embodiments, the host cell is selected from a plant cell, a microbial cell, and a microalgal cell. In a further aspect, provided is a method of producing a recombinant cell that produces an altered fatty acid profile, the method comprising transforming the cell with a nucleic acid encoding a FATA protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61 and wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A). In a further aspect, provided is a host cell produced according to such a method. In some embodiments, the host cell is selected from a plant cell, a microbial cell, and a microalgal cell. In a further aspect, provided is a method for producing an oil or oil-derived product, the method comprising cultivating a host cell encoding a FATA protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61 and wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A) and extracting oil produced thereby, optionally wherein the cultivation is by heterotrophic growth on sugar. In varying embodiments, the methods further comprise producing a fatty acid, fuel, chemical, food, or other oil-derived product from the oil. In varying embodiments, the host cell produces at least 2-fold the amount of C18:0 and/or C18:1 fatty acids compared to a host cell that expresses the wild-type protein. In a further aspect, further provided is an oil produced by the method of expressing in a host cell a polynucleotide encoding a FATA protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61 and wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A), optionally having a fatty acid profile comprising at least 20% C8, C10, C12, C14, C16 or C18 (e.g., C18:0 and/or C18:1) fatty acids. In varying embodiments, the oil is produced by a microalgae, has a microalgal sterol profile, and/or optionally, lacks C24-alpha sterols. Further provided is an oil-derived product, optionally a fatty acid, fuel, chemical, food, or other oil-derived product from the oil produced by the method of expressing in a host cell a polynucleotide encoding a FATA protein having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO:61 and wherein the protein has an alanine (A) at one or both positions corresponding to position 126 of SEQ ID NO: 61 (D124A) and 211 of SEQ ID NO: 61 (D209A).
Description of Illustrative Embodiments DefinitionsAs used with respect to nucleic acids, the term “isolated” refers to a nucleic acid that is free of at least one other component that is typically present with the naturally occurring nucleic acid. Thus, a naturally occurring nucleic acid is isolated if it has been purified away from at least one other component that occurs naturally with the nucleic acid.
A “cell oil” or “natural fat” shall mean a predominantly triglyceride oil obtained from an organism, where the oil has not undergone blending with another natural or synthetic oil, or fractionation so as to substantially alter the fatty acid profile of the triglyceride. In connection with an oil comprising triglycerides of a particular regiospecificity, the cell oil or natural fat has not been subjected to interesterification or other synthetic process to obtain that regiospecific triglyceride profile, rather the regiospecificity is produced naturally, by a cell or population of cells. In connection with a cell oil or natural fat, and as used generally throughout the present disclosure, the terms oil and fat are used interchangeably, except where otherwise noted. Thus, an “oil” or a “fat” can be liquid, solid, or partially solid at room temperature, depending on the makeup of the substance and other conditions. Here, the term “fractionation” means removing material from the oil in a way that changes its fatty acid profile relative to the profile produced by the organism, however accomplished. The terms “cell oil” and “natural fat” encompass such oils obtained from an organism, where the oil has undergone minimal processing, including refining, bleaching and/or degumming, which does not substantially change its triglyceride profile. A cell oil can also be a “noninteresterified cell oil”, which means that the cell oil has not undergone a process in which fatty acids have been redistributed in their acyl linkages to glycerol and remain essentially in the same configuration as when recovered from the organism.
“Exogenous gene” shall mean a nucleic acid that codes for the expression of an RNA and/or protein that has been introduced into a cell (e.g. by transformation/transfection), and is also referred to as a “transgene”. A cell comprising an exogenous gene may be referred to as a recombinant cell, into which additional exogenous gene(s) may be introduced. The exogenous gene may be from a different species (and so heterologous), or from the same species (and so homologous), relative to the cell being transformed. Thus, an exogenous gene can include a homologous gene that occupies a different location in the genome of the cell or is under different control, relative to the endogenous copy of the gene. An exogenous gene may be present in more than one copy in the cell. An exogenous gene may be maintained in a cell, for example, as an insertion into the genome (nuclear or plastid) or as an episomal molecule.
“Fatty acids” shall mean free fatty acids, fatty acid salts, or fatty acyl moieties in a glycerolipid. It will be understood that fatty acyl groups of glycerolipids can be described in terms of the carboxylic acid or anion of a carboxylic acid that is produced when the triglyceride is hydrolyzed or saponified.
“Microalgae” are microbial organisms that contain a chloroplast or other plastid, and optionally that are capable of performing photosynthesis, or a prokaryotic microbial organism capable of performing photosynthesis. Microalgae include obligate photoautotrophs, which cannot metabolize a fixed carbon source as energy, as well as heterotrophs, which can live solely off of a fixed carbon source. Microalgae include unicellular organisms that separate from sister cells shortly after cell division, such as Chlamydomonas, as well as microbes such as, for example, Volvox, which is a simple multicellular photosynthetic microbe of two distinct cell types. Microalgae include cells such as Chlorella, Dunaliella, and Prototheca. Microalgae also include other microbial photosynthetic organisms that exhibit cell-cell adhesion, such as Agmenellum, Anabaena, and Pyrobotrys. Microalgae also include obligate heterotrophic microorganisms that have lost the ability to perform photosynthesis, such as certain dinoflagellate algae species and species of the genus Prototheca.
An “oleaginous” cell is a cell capable of producing at least 20% lipid by dry cell weight, naturally or through recombinant or classical strain improvement. An “oleaginous microbe” or “oleaginous microorganism” is a microbe, including a microalga that is oleaginous.
The term “percent sequence identity,” in the context of two or more amino acid or nucleic acid sequences, refers to two or more sequences or subsequences that are the same or have a specified percentage of amino acid residues or nucleotides that are the same, when compared and aligned for maximum correspondence, as measured using a sequence comparison algorithm or by visual inspection. For sequence comparison to determine percent nucleotide or amino acid identity, typically one sequence acts as a reference sequence, to which test sequences are compared. When using a sequence comparison algorithm, test and reference sequences are input into a computer, subsequence coordinates are designated, if necessary, and sequence algorithm program parameters are designated. The sequence comparison algorithm then calculates the percent sequence identity for the test sequence(s) relative to the reference sequence, based on the designated program parameters. Optimal alignment of sequences for comparison can be conducted using the NCBI BLAST software (ncbi.nlm.nih.gov/BLAST/) set to default parameters. For example, to compare two nucleic acid sequences, one may use blastn with the “BLAST 2 Sequences” tool Version 2.0.12 (Apr. 21, 2000) set at the following default parameters: Matrix: BLOSUM62; Reward for match: 1; Penalty for mismatch: −2; Open Gap: 5 and Extension Gap: 2 penalties; Gap x drop-off: 50; Expect: 10; Word Size: 11; Filter: on. For a pairwise comparison of two amino acid sequences, one may use the “BLAST 2 Sequences” tool Version 2.0.12 (Apr. 21, 2000) with blastp set, for example, at the following default parameters: Matrix: BLOSUM62; Open Gap: 11 and Extension Gap: 1 penalties; Gap x drop-off 50; Expect: 10; Word Size: 3; Filter: on.
Numbering of a given amino acid polymer or nucleic acid polymer “corresponds to” or is “relative to” the numbering of a selected amino acid polymer or nucleic acid polymer when the position of any given polymer component (e.g., amino acid, nucleotide, also referred to generically as a “residue”) is designated by reference to the same or to an equivalent position (e.g., based on an optimal alignment or a consensus sequence) in the selected amino acid or nucleic acid polymer, rather than by the actual numerical position of the component in the given polymer.
A “variant” is a polypeptide comprising a sequence which differs in one or more amino acid position(s) from that of a parent polypeptide sequence (e.g., by substitution, deletion, or insertion). A variant may comprise a sequence which differs from the parent polypeptides sequence in up to 40% of the total number of residues of the parent polypeptide sequence, such as in up to 40%, 35%, 30%, 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3% 2% or 1% of the total number of residues of the parent polypeptide sequence. For example, a variant of a 400 amino acid polypeptide sequence comprises a sequence which differs in up to 40% of the total number of residues of the parent polypeptide sequence, that is, in up to 160 amino acid positions within the 400 amino acid polypeptide sequence (such as in 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 78, 79, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, or 160 amino acid positions within the reference sequence.
“Naturally occurring” as applied to a composition that can be found in nature as distinct from being artificially produced by man. For example, a polypeptide or polynucleotide that is present in an organism (including viruses, bacteria, protozoa, insects, plants or mammalian tissue) that can be isolated from a source in nature and which has not been intentionally modified by man in the laboratory is naturally occurring. “Non-naturally occurring” (also termed “synthetic” or “artificial”) as applied to an object means that the object is not naturally-occurring—i.e., the object cannot be found in nature as distinct from being artificially produced by man.
In connection with a cell oil, a “profile” is the distribution of particular species or triglycerides or fatty acyl groups within the oil. A “fatty acid profile” is the distribution of fatty acyl groups in the triglycerides of the oil without reference to attachment to a glycerol backbone. Fatty acid profiles are typically determined by conversion to a fatty acid methyl ester (FAME), followed by gas chromatography (GC) analysis with flame ionization detection (FID). The fatty acid profile can be expressed as one or more percent of a fatty acid in the total fatty acid signal determined from the area under the curve for that fatty acid. FAME-GC-FID measurement approximate weight percentages of the fatty acids.
As used herein, an oil is said to be “enriched” in one or more particular fatty acids if there is at least a 10% increase in the mass of that fatty acid in the oil relative to the non-enriched oil. For example, in the case of a cell expressing a heterologous FatB gene described herein, the oil produced by the cell is said to be enriched in, e.g., C8 and C16 fatty acids if the mass of these fatty acids in the oil is at least 10% greater than in oil produced by a cell of the same type that does not express the heterologous FatB gene (e.g., wild type oil).
“Recombinant” is a cell, nucleic acid, protein or vector that has been modified due to the introduction of an exogenous nucleic acid or the alteration of a native nucleic acid. Thus, e.g., recombinant (host) cells can express genes that are not found within the native (non-recombinant) form of the cell or express native genes differently than those genes are expressed by a non-recombinant cell. Recombinant cells can, without limitation, include recombinant nucleic acids that encode a gene product or suppression elements such as mutations, knockouts, antisense, interfering RNA (RNAi) or dsRNA that reduce the levels of active gene product in a cell. A “recombinant nucleic acid” is a nucleic acid originally formed in vitro, in general, by the manipulation of nucleic acid, e.g., using polymerases, ligases, exonucleases, and endonucleases, using chemical synthesis, or otherwise is in a form not normally found in nature. Recombinant nucleic acids may be produced, for example, to place two or more nucleic acids in operable linkage. Thus, an isolated nucleic acid or an expression vector formed in vitro by nucleic by ligating DNA molecules that are not normally joined in nature, are both considered recombinant herein. Recombinant nucleic acids can also be produced in other ways; e.g., using chemical DNA synthesis. Once a recombinant nucleic acid is made and introduced into a host cell or organism, it may replicate using the in vivo cellular machinery of the host cell; however, such nucleic acids, once produced recombinantly, although subsequently replicated intracellularly, are still considered recombinant herein. Similarly, a “recombinant protein” is a protein made using recombinant techniques, i.e., through the expression of a recombinant nucleic acid.
Embodiments relate to the use of novel FatB acyl-ACP thioesterase genes (e.g. in the form of cDNA, vectors, and constructs in vitro or in host cells) gene-variants, and peptides isolated from plants which can be expressed in a host cell in order to alter the fatty acid profile of an oil produced by the cell. The genes were discovered by obtaining cDNA from various plant species and transforming a model organism —the obligate heterotrophic microalga, Prototheca moriformis. Although P. moriformis was used to screen the FatB genes for ability to the alter fatty acid profile, the genes and corresponding gene-products are useful in a wide variety of host cells. For example, the genes can be expressed in bacteria, other microalgae, or higher plants. The genes can be expressed in higher plants according to the methods of U.S. Pat. Nos. 5,850,022; 5,723,761; 5,639,790; 5,807,893; 5,455,167; 5,654,495; 5,512,482; 5,298,421; 5,667,997; 5,344,771; and 5,304,481. The fatty acids can be further converted to triglycerides, fatty aldehydes, fatty alcohols and other oleochemicals either synthetically or biosynthetically.
Additionally, in the course of obtaining the novel FatB sequences, we discovered that certain N-terminal deletions in the FatB cDNAs led to desirably altered fatty acid profiles in the microalgal model.
In an embodiment, there is a polynucleotide comprising a nucleic acid sequence operably linked to a heterologous expression control sequence, wherein said nucleic acid sequence is selected from the group consisting of SEQ ID NOs: 19-36, a sequence encoding the amino acid sequence of the group consisting of SEQ ID NOs: 1-18, or a variant thereof with acyl-ACP thioesterase activity when expressed in a plastidic oleaginous cell.
In an embodiment, triglycerides are produced by a host cell expressing a novel FatB gene of Table 1. A triglyceride-containing cell oil can be recovered from the host cell. The cell oil can be refined, degummed, bleached and/or deodorized. The oil, in its natural or processed form, can be used for foods, chemicals, fuels, cosmetics, plastics, and other uses.
The genes can be used in a variety of genetic constructs including plasmids or other vectors for expression or recombination in a host cell. The genes can be codon optimized for expression in a target host cell (e.g., using the codon usage tables of Tables 2-5.) For example, at least 60, 65, 70, 75, 80, 85, 90, 95 or 100% of the codons used can be the most preferred codon according to Table 2, 3, 4 or 5. Alternately, at least 60, 65, 70, 75, 80, 85, 90, 95 or 100% of the codons used can be the first or second most preferred codon according to Table 2, 3, or 5. The proteins produced by the genes can be used in vivo or in purified form.
For example, the gene can be prepared in an expression vector comprising an operably linked promoter and 5′UTR. Where a plastidic cell is used as the host, a suitably active plastid targeting peptide (also “transit peptide”) can be fused to the FATB gene, as in the examples below. Transit peptides are denoted by underlined or outlined text in some of the FATB peptide sequences that appear below. Generally, for the newly identified FATB genes, there are roughly 50 amino acids at the N-terminal that constitute a plastid transit peptide, which are responsible for transporting the enzyme to the chloroplast. In the examples below, this transit peptide is replaced with a 38 amino acid sequence (SEQ ID NO: 37) that is effective in Prototheca moriformis host cells for transporting the enzyme to the plastids of those cells. Thus, we contemplate deletions and fusion proteins in order to optimize enzyme activity in a given host cell. For example, a transit peptide from the host or related species may be used instead of that of the newly discovered plant genes described here. In general, plastid targeting peptides are less conserved than the enzymatic domains of FATB genes. Plastid targeting peptides can be substituted with other sequences such as those found in plant-derived sequences of plastid targeting genes (e.g., those for FATA, FATB, SAD or KAS genes) in the ThYme database of thioesters-active enzymes hosted by Iowa State University/NSF Engineering Research Center for Biorenewable Chemicals. Accordingly, certain embodiments describe percent identity to gene or protein sequences to FATB genes lacking the plastid targeting peptide.
A selectable marker gene may be included in the vector to assist in isolating a transformed cell. Examples of selectable markers useful in microalgae include sucrose invertase, antibiotic resistance, and thiamine synthesis genes.
The gene sequences disclosed can also be used to prepare antisense, or inhibitory RNA (e.g., RNAi or hairpin RNA) to inhibit complementary genes in a plant or other organism.
FatB genes found to be useful in producing desired fatty acid profiles in a cell are summarized below in Table 1. Nucleic acids or proteins having the sequence of SEQ ID NOS: 19-36 can be used to alter the fatty acid profile of a recombinant cell. Variant nucleic acids can also be used; e.g., variants having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NOS: 19-36. Codon optimization of the genes for a variety of host organisms is contemplated, as is the use of gene fragments. Preferred codons for Prototheca strains and for Chlorella protothecoides are shown below in Tables 2 and 3, respectively. Codon usage for Cuphea wrightii is shown in Table 4. Codon usage for Arabidopsis is shown in Table 5; for example, the most preferred of codon for each amino acid can be selected. Codon tables for other organisms including microalgae and higher plants are known in the art. In some embodiments, the first and/or second most preferred Prototheca codons are employed for codon optimization. In specific embodiments, the novel amino acid sequences contained in the sequence listings below are converted into nucleic acid sequences according to the preferred codon usage in Prototheca, Chlorella, Cuphea wrightii, or Arabidopsis as set forth in tables 2 through 5 or nucleic acid sequences having at least 65, 70, 80, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to these derived nucleic acid sequences.
In embodiments, there is protein or a nucleic acid encoding a protein having any of SEQ ID NOS: 1-18. In an embodiment, there is protein or a nucleic acid encoding a protein having at least 80, 85, 85.1, 85.2, 85.3,85.4, 85.5, 86, 86.5, 86.6, 86.7, 87, 87.5, 87.6, 87.7, 87.8, 87.9, 88, 89, 90, 91, 92, 92.5, 92.6, 92.7, 92.8, 92.9, 93, 93.5, 93.6, 93.7, 93.8, 94, 94.1, 94.2, 94.3, 94.4, 94.5, 94.6, 94.7, 94.8, 94.9, 95, 95.1, 95.2, 95.3, 95.4, 95.6, 95.7, 95.8, 95.9, 96, 96.1, 96.2, 96.3, 96.4, 96.5, 97, 98, 99, or 100% sequence identity with any of SEQ ID NOS: 1-18. An embodiment comprises a fragment of any of the above-described proteins or nucleic acids (including fragments of protein or nucleic acid variants), wherein the protein fragment has acyl-ACP thioesterase activity or the nucleic acid fragment encodes such a protein fragment. In other embodiments, the fragment includes a domain of an acyl-ACP thioesterase that mediates a particular function, e.g., a specificity-determining domain. Illustrative fragments can be produced by C-terminal and/or N-terminal truncations and include at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% of the full-length sequences disclosed herein.
In certain embodiments, percent sequence identity for variants of the nucleic acids or proteins discussed above can be calculated by using the full-length nucleic acid sequence (e.g., one of SEQ ID NOS: 19-36) or full-length amino acid sequence (e.g., one of SEQ ID NOS: 1-18) as the reference sequence and comparing the full-length test sequence to this reference sequence. In some embodiments relating to fragments, percent sequence identity for variants of nucleic acid or protein fragments can be calculated over the entire length of the fragment.
The nucleic acids can be in isolated form, or part of a vector or other construct, chromosome or host cell. It has been found that is many cases the full length gene (and protein) is not needed; for example, deletion of some or all of the N-terminal hydrophobic domain (typically an 18 amino acid domain starting with LPDW) (SEQ ID NO:62) yields a still-functional gene. In addition, fusions of the specificity determining regions of the genes in Table 1 with catalytic domains of other acyl-ACP thioesterases can yield functional genes. Certain embodiments encompass functional fragments (e.g., specificity determining regions) of the disclosed nucleic acid or amino acids fused to heterologous acyl-ACP thioesterase nucleic acid or amino acid sequences, respectively.
The host cell can be a single cell (e.g., microalga, bacteria, yeast) or part of a multicellular organism such as a plant or fungus. Methods for expressing Fatb genes in a plant are described, e.g., in U.S. Pat. Nos. 5,850,022; 5,723,761; 5,639,790; 5,807,893; 5,455,167; 5,654,495; 5,512,482; 5,298,421; 5,667,997; 5,344,771; and 5,304,481, or can be obtained using other techniques generally known in plant biotechnology. Engineering of oleaginous microbes including those of Chlorophyta is disclosed in WO2010/063032, WO2011/150411, and WO2012/106560 and in the examples below.
Examples of oleaginous host cells include plant cells and microbial cells having a type II fatty acid biosynthetic pathway, including plastidic oleaginous cells such as those of oleaginous algae. Specific examples of microalgal cells include heterotrophic or obligate heterotrophic microalgae of the phylum Chlorophtya, the class Trebouxiophytae, the order Chlorellales, or the family Chlorellacae. Examples of oleaginous microalgae are provided in Published PCT Patent Applications WO2008/151149, WO2010/06032, WO2011/150410, and WO2011/150411, including species of Chlorella and Prototheca, a genus comprising obligate heterotrophs. The oleaginous cells can be, for example, capable of producing 20, 25, 30, 40, 50, 60, 70, 80, 85, or about 90% oil by cell weight, ±5%. Optionally, the oils produced can be low in DHA or EPA fatty acids. For example, the oils can comprise less than 5%, 2%, or 1% DHA and/or EPA. The above-mentioned publications also disclose methods for cultivating such cells and extracting oil, especially from microalgal cells; such methods are applicable to the cells disclosed herein and incorporated by reference for these teachings. When microalgal cells are used they can be cultivated autotrophically (unless an obligate heterotroph) or in the dark using a sugar (e.g., glucose, fructose and/or sucrose). In any of the embodiments described herein, the cells can be heterotrophic cells comprising an exogenous invertase gene so as to allow the cells to produce oil from a sucrose feedstock. Alternately, or in addition, the cells can metabolize xylose from cellulosic feedstocks. For example, the cells can be genetically engineered to express one or more xylose metabolism genes such as those encoding an active xylose transporter, a xylulose-5-phosphate transporter, a xylose isomerase, a xylulokinase, a xylitol dehydrogenase and a xylose reductase. See WO2012/154626, “GENETICALLY ENGINEERED MICROORGANISMS THAT METABOLIZE XYLOSE”, published Nov. 15, 2012. The cells can be cultivated on a depolymerized cellulosic feedstock such as acid or enzyme hydrolyzed bagasse, sugar beet pulp, corn stover, wood chips, sawdust or switchgrass. Optionally, the cells can be cultivated on a depolymerized cellulosic feedstock comprising glucose and at least 5, 10, 20, 30 or 40% xylose, while producing at least 20% lipid by dry weight. Optionally, the lipid comprises triglycerides having a fatty acid profile characterized by at least 10, 15 or 20% C12:0
Oils and Related ProductsThe oleaginous cells express one or more exogenous genes encoding fatty acid biosynthesis enzymes. As a result, some embodiments feature cell oils that were not obtainable from a non-plant or non-seed oil, or not obtainable at all.
The oleaginous cells produce a storage oil, which is primarily triacylglyceride and may be stored in storage bodies of the cell. A raw oil may be obtained from the cells by disrupting the cells and isolating the oil. WO2008/151149, WO2010/06032, WO2011/150410, and WO2011/1504 disclose heterotrophic cultivation and oil isolation techniques. For example, oil may be obtained by cultivating, drying and pressing the cells. Methods for pressing cells are given in WO2010/120939. The oils produced may be refined, bleached and deodorized (RBD) as known in the art or as described in WO2010/120939. The raw or RBD oils may be used in a variety of food, chemical, and industrial products or processes. After recovery of the oil, a valuable residual biomass remains. Uses for the residual biomass include the production of paper, plastics, absorbents, adsorbents, as animal feed, for human nutrition, or for fertilizer.
Where a fatty acid profile of a triglyceride (also referred to as a “triacylglyceride” or “TAG”) cell oil is given here, it will be understood that this refers to a nonfractionated sample of the storage oil extracted from the cell analyzed under conditions in which phospholipids have been removed or with an analysis method that is substantially insensitive to the fatty acids of the phospholipids (e.g. using chromatography and mass spectrometry). The oil may be subjected to an RBD process to remove phospholipids, free fatty acids and odors yet have only minor or negligible changes to the fatty acid profile of the triglycerides in the oil. Because the cells are oleaginous, in some cases the storage oil will constitute the bulk of all the TAGs in the cell.
The stable carbon isotope value δ13C is an expression of the ratio of 13C/12C relative to a standard (e.g. PDB, carbonite of fossil skeleton of Belemnite americana from Peedee formation of South Carolina). The stable carbon isotope value δ13C (0/00) of the oils can be related to the δ13C value of the feedstock used. In some embodiments, the oils are derived from oleaginous organisms heterotrophically grown on sugar derived from a C4 plant such as corn or sugarcane. In some embodiments the δ13C (0/00) of the oil is from −10 to −17 0/00 or from −13 to −16 0/00.
The oils produced according to the above methods in some cases are made using a microalgal host cell. As described above, the microalga can be, without limitation, fall in the classification of Chlorophyta, Trebouxiophyceae, Chlorellales, Chlorellaceae, or Chlorophyceae. It has been found that microalgae of Trebouxiophyceae can be distinguished from vegetable oils based on their sterol profiles. Oil produced by Chlorella protothecoides was found to produce sterols that appeared to be brassicasterol, ergosterol, campesterol, stigmasterol, and β-sitosterol, when detected by GC-MS. However, it is believed that all sterols produced by Chlorella have C24β stereochemistry. Thus, it is believed that the molecules detected as campesterol, stigmasterol, and β-sitosterol, are actually 22,23-dihydrobrassicasterol, proferasterol and clionasterol, respectively. Thus, the oils produced by the microalgae described above can be distinguished from plant oils by the presence of sterols with C24β stereochemistry and the absence of C24α stereochemistry in the sterols present. For example, the oils produced may contain 22, 23-dihydrobrassicasterol while lacking campesterol; contain clionasterol, while lacking in β-sitosterol, and/or contain poriferasterol while lacking stigmasterol. Alternately, or in addition, the oils may contain significant amounts of Δ7-poriferasterol.
In one embodiment, the oils provided herein are not vegetable oils. Vegetable oils are oils extracted from plants and plant seeds. Vegetable oils can be distinguished from the non-plant oils provided herein on the basis of their oil content. A variety of methods for analyzing the oil content can be employed to determine the source of the oil or whether adulteration of an oil provided herein with an oil of a different (e.g. plant) origin has occurred. The determination can be made on the basis of one or a combination of the analytical methods. These tests include but are not limited to analysis of one or more of free fatty acids, fatty acid profile, total triacylglycerol content, diacylglycerol content, peroxide values, spectroscopic properties (e.g. UV absorption), sterol profile, sterol degradation products, antioxidants (e.g. tocopherols), pigments (e.g. chlorophyll), d13C values and sensory analysis (e.g. taste, odor, and mouth feel). Many such tests have been standardized for commercial oils such as the Codex Alimentarius standards for edible fats and oils.
Sterol profile analysis is a particularly well-known method for determining the biological source of organic matter. Campesterol, b-sitosterol, and stigmasterol are common plant sterols, with b-sitosterol being a principle plant sterol. For example, b-sitosterol was found to be in greatest abundance in an analysis of certain seed oils, approximately 64% in corn, 29% in rapeseed, 64% in sunflower, 74% in cottonseed, 26% in soybean, and 79% in olive oil (Gul et al. J. Cell and Molecular Biology 5:71-79, 2006).
Oil isolated from Prototheca moriformis strain UTEX1435 were separately clarified (CL), refined and bleached (RB), or refined, bleached and deodorized (RBD) and were tested for sterol content according to the procedure described in JAOCS vol. 60, no. 8, August 1983. Results of the analysis are shown below (units in mg/100 g):
These results show three striking features. First, ergosterol was found to be the most abundant of all the sterols, accounting for about 50% or more of the total sterols. The amount of ergosterol is greater than that of campesterol, β-sitosterol, and stigmasterol combined. Ergosterol is steroid commonly found in fungus and not commonly found in plants, and its presence particularly in significant amounts serves as a useful marker for non-plant oils. Secondly, the oil was found to contain brassicasterol. With the exception of rapeseed oil, brassicasterol is not commonly found in plant based oils. Thirdly, less than 2% β-sitosterol was found to be present. β-sitosterol is a prominent plant sterol not commonly found in microalgae, and its presence particularly in significant amounts serves as a useful marker for oils of plant origin. In summary, Prototheca moriformis strain UTEX1435 has been found to contain both significant amounts of ergosterol and only trace amounts of β-sitosterol as a percentage of total sterol content. Accordingly, the ratio of ergosterol: β-sitosterol or in combination with the presence of brassicasterol can be used to distinguish this oil from plant oils.
In some embodiments, the oil content of an oil provided herein contains, as a percentage of total sterols, less than 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% β-sitosterol. In other embodiments the oil is free from β-sitosterol.
In some embodiments, the oil is free from one or more of β-sitosterol, campesterol, or stigmasterol. In some embodiments the oil is free from β-sitosterol, campesterol, and stigmasterol. In some embodiments the oil is free from campesterol. In some embodiments the oil is free from stigmasterol.
In some embodiments, the oil content of an oil provided herein comprises, as a percentage of total sterols, less than 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% 24-ethylcholest-5-en-3-ol. In some embodiments, the 24-ethylcholest-5-en-3-ol is clionasterol. In some embodiments, the oil content of an oil provided herein comprises, as a percentage of total sterols, at least 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% clionasterol.
In some embodiments, the oil content of an oil provided herein contains, as a percentage of total sterols, less than 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% 24-methylcholest-5-en-3-ol. In some embodiments, the 24-methylcholest-5-en-3-ol is 22, 23-dihydrobrassicasterol. In some embodiments, the oil content of an oil provided herein comprises, as a percentage of total sterols, at least 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% 22,23-dihydrobrassicasterol.
In some embodiments, the oil content of an oil provided herein contains, as a percentage of total sterols, less than 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% 5,22-cholestadien-24-ethyl-3-ol. In some embodiments, the 5, 22-cholestadien-24-ethyl-3-ol is poriferasterol. In some embodiments, the oil content of an oil provided herein comprises, as a percentage of total sterols, at least 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% poriferasterol.
In some embodiments, the oil content of an oil provided herein contains ergosterol or brassicasterol or a combination of the two. In some embodiments, the oil content contains, as a percentage of total sterols, at least 5%, 10%, 20%, 25%, 35%, 40%, 45%, 50%, 55%, 60%, or 65% ergosterol. In some embodiments, the oil content contains, as a percentage of total sterols, at least 25% ergosterol. In some embodiments, the oil content contains, as a percentage of total sterols, at least 40% ergosterol. In some embodiments, the oil content contains, as a percentage of total sterols, at least 5%, 10%, 20%, 25%, 35%, 40%, 45%, 50%, 55%, 60%, or 65% of a combination of ergosterol and brassicasterol.
In some embodiments, the oil content contains, as a percentage of total sterols, at least 1%, 2%, 3%, 4% or 5% brassicasterol. In some embodiments, the oil content contains, as a percentage of total sterols less than 10%, 9%, 8%, 7%, 6%, or 5% brassicasterol.
In some embodiments the ratio of ergosterol to brassicasterol is at least 5:1, 10:1, 15:1, or 20:1.
In some embodiments, the oil content contains, as a percentage of total sterols, at least 5%, 10%, 20%, 25%, 35%, 40%, 45%, 50%, 55%, 60%, or 65% ergosterol and less than 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% β-sitosterol. In some embodiments, the oil content contains, as a percentage of total sterols, at least 25% ergosterol and less than 5% β-sitosterol. In some embodiments, the oil content further comprises brassicasterol.
Sterols contain from 27 to 29 carbon atoms (C27 to C29) and are found in all eukaryotes. Animals exclusively make C27 sterols as they lack the ability to further modify the C27 sterols to produce C28 and C29 sterols. Plants however are able to synthesize C28 and C29 sterols, and C28/C29 plant sterols are often referred to as phytosterols. The sterol profile of a given plant is high in C29 sterols, and the primary sterols in plants are typically the C29 sterols b-sitosterol and stigmasterol. In contrast, the sterol profile of non-plant organisms contain greater percentages of C27 and C28 sterols. For example the sterols in fungi and in many microalgae are principally C28 sterols. The sterol profile and particularly the striking predominance of C29 sterols over C28 sterols in plants has been exploited for determining the proportion of plant and marine matter in soil samples (Huang, Wen-Yen, Meinschein W. G., “Sterols as ecological indicators”; Geochimica et Cosmochimia Acta. Vol 43. pp 739-745).
In some embodiments the primary sterols in the microalgal oils provided herein are sterols other than b-sitosterol and stigmasterol. In some embodiments of the microalgal oils, C29 sterols make up less than 50%, 40%, 30%, 20%, 10%, or 5% by weight of the total sterol content.
In some embodiments the microalgal oils provided herein contain C28 sterols in excess of C29 sterols. In some embodiments of the microalgal oils, C28 sterols make up greater than 50%, 60%, 70%, 80%, 90%, or 95% by weight of the total sterol content. In some embodiments the C28 sterol is ergosterol. In some embodiments the C28 sterol is brassicasterol.
In embodiments, oleaginous cells expressing one or more of the genes of Table 1 can produce an oil with at least 20, 40, 60 or 70% of C8, C10, C12, C14 or C16 fatty acids. In a specific embodiment, the level of myristate (C14:0) in the oil is greater than 30%.
Thus, in embodiments, there is a process for producing an oil, triglyceride, fatty acid, or derivative of any of these, comprising transforming a cell with any of the nucleic acids discussed herein. In another embodiment, the transformed cell is cultivated to produce an oil and, optionally, the oil is extracted. Oil extracted in this way can be used to produce food, oleochemicals or other products.
The oils discussed above alone or in combination are useful in the production of foods, fuels and chemicals (including plastics, foams, films, etc). The oils, triglycerides, fatty acids from the oils may be subjected to C—H activation, hydroamino methylation, methoxy-carbonation, ozonolysis, enzymatic transformations, epoxidation, methylation, dimerization, thiolation, metathesis, hydro-alkylation, lactonization, or other chemical processes.
After extracting the oil, a residual biomass may be left, which may have use as a fuel, as an animal feed, or as an ingredient in paper, plastic, or other product. For example, residual biomass from heterotrophic algae can be used in such products.
Deletion Mutants of FATB Genes that Enhance Production of Mid-Chain Fatty Acids in Host Cells
In another embodiment, there is a method for increasing the production of C12 or C10 fatty acids. The method comprises producing a polynucleotide having a sequence encoding a FATB acyl-ACP thioesterase but encoding a deletion mutation in the region corresponding to amino acids 66-98 of the SalFATB2 gene (SEQ ID NO: 8); i.e., a deletion in the FATB region corresponding to that characterized by SEQ ID NO: 42. In some cases, the region of the deletion mutant for the starting FATB already contains gaps; in this case, further residues in the region can be removed. For example, UcFATB2 has a 2-residue gap at positions 95-96 relative to SalFatB2, UcFatB1 has a 6-residue gap at positions 92-97 relative to SalFatB2, and LbeFatB1 has a 4-residue gap at positions 94-97 relative to SalFatB2. The full 32 amino acid deletion or shorter deletions (i.e., of 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 or 31 amino acid residues) may also be effective in increasing C12 fatty acids in the FATB enzymes disclosed here or others known in the art (e.g., those with at least 80, 85, 90 or 95% identity to one of SEQ ID NOs: 1-18); this can readily be determined using the techniques disclosed here including the Examples.
Vectors containing genes that encode the deletion mutants can be expressed in an oleaginous host cell (single or multicellular) and compared to an untransformed cell to select mutants that increase the production of mid-chain fatty acids by the cell. This can be determined by extracting the oil and using has chromatography techniques.
Accordingly, in an embodiment, there is a method for increasing the production of C10-C14 fatty acids in a cell. The method comprises producing or providing an exogenous polynucleotide, the exogenous polynucleotide comprising an, optionally heterologous, control sequence fused to a coding region that encodes a plastid targeting sequence and a mutant FATB acyl-ACP thioesterase enzyme domain. The FATB acyl-ACP thioesterase enzyme domain has a deletion in the region corresponding to amino acids 66-98 of SEQ ID NO: 8. The exogenous polynucleotide is expressed in an oleaginous host cell. As a result of the expression, the host cell produces an oil that is enriched in C12 fatty acids, relative to a control cell lacking the exogenous polynucleotide. In specific embodiments, the sum of C10 and C12 fatty acids in the fatty acid profile of the oil is increased by at least 10, 20, 30, 50, 100, 150, or 200%. For example, the amount of C12 fatty acids in the oil is increased by at least 2-fold relative to the control cell. The starting FATB gene is not the CcFATB4 gene (SEQ ID NO: 46), because this gene already has a gap spanning the domain in which the deletion is made. In a related embodiment, the deletion leads to an increase in C8 and/or C10 fatty acids.
In an embodiment, there is a polynucleotide encoding a protein sequence having at least 75, 80, 85, 85.5, 86, 86.5, 87, 87.5, 88, 88.5, 89, 89.5, 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5 or 99% amino acid identity to any of SEQ ID NOs: 43-46, 50, 51, 54 or 55. The polynucleotide can comprise at least 60,65,70, 75, 80, 85, 85.5, 86, 86.5, 87, 87.5, 88, 88.5, 89, 89.5, 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5 or 99% sequence identity to any of SEQ ID NOs 47, 48, 52, or 56, or equivalent sequence by virtue of the degeneracy of the genetic code. The sequence has a deletion in the region corresponding to amino acids 66-98, and is not that of CcFatB4 (SEQ ID NO: 46). In related embodiments, there is a protein encoded by one of the above sequences, a vector for transforming a host cell, or a host cell expressing one of the sequences. There is also a method of producing an oil comprising expressing one of these sequences in an oleaginous host cell, cultivating the cell, and isolating an oil from the cell. The oil recovered can be elevated in C12 fatty acids 10, 20, 50, 100, 150, 200% or more relative to a control cell lacking the polynucleotide. Example 3 demonstrates the increase in C12:0 fatty acids resulting from expression of the deletion mutants in a Eukaryotic microalga, relative to controls lacking the deletion.
The polynucleotide sequence can be codon optimized for a variety of organisms including according to Tables 2-5.
In accordance with an embodiment, a method of genetically engineering a cell includes expressing in the cell, a polynucleotide that encodes a protein having at least 65, 70, 80, 85, 86, 86, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to any of SEQ ID NOS: 40 to 43, 50, 51, 54 or 55; or has at least 65, 70, 80, 85, 86, 86, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% sequence identity to SEQ ID NO: 44, 45, 52 or 56, or equivalent sequence by virtue of the degeneracy of the genetic code. In a specific embodiment, a method of genetically engineering a cell includes expressing in the cell, a polynucleotide that encodes a protein having at least 86.7% sequence identity to 42, at least 80.7% sequence identity to 43, at least 88.2% sequence identity SEQ ID NOS: 51.
EXAMPLE 1 Discovery of Novel FATB SequencesRNA was extracted from dried plant seeds and submitted for paired-end sequencing using the Illumina Hiseq 2000 platform. RNA sequence reads were assembled into corresponding seed transcriptomes using the Trinity software package and putative thioesterase-containing cDNA contigs were identified by mining transcriptomes for sequences with homology to known thioesterases. In some cases, these in silico identified putative thioesterase cDNAs were verified by direct reverse transcription PCR analysis using seed RNA and primer pairs targeting full-length thioesterase cDNAs. The resulting amplified products were cloned and sequenced de novo to confirm authenticity of identified thioesterase genes and to identify sequence variants arising from expression of different gene alleles or diversity of sequences within a population of seeds. For some sequences, a high-confidence, full-length transcript was assembled using Trinity and reverse transcription was not deemed to be necessary. The resulting amino acid sequences of all new putative FATB thioesterases were subjected to phylogenetic analyses using published full-length (Mayer and Shanklin, 2007) and truncated (THYME database) sequences as well as an extensive in-house phylogeny developed at Solazyme from FATB sequences identified in numerous oilseed transcriptomes. The in-house phylogeny comprising the acyl-ACP FATB thioesterases allows for prediction, in many cases, of the midchain specificity for each thioesterase; the FATBs predicted to be involved in biosynthesis of C8-C12 fatty acids were pursued.
The amino acid sequence and nucleic acid CDSs (native to the plant and codon optimized for Prototheca moriformis) of the novel FatB genes with and without their N-terminal plastid targeting peptides are shown in Table 1, above.
EXAMPLE 2 Expression of Transforming Vectors Expressing Acyl-ACP FATB ThioesterasesThe nine acyl-ACP FATB thioesterase genes of Example 1 were synthesized in a codon-optimized form to reflect Prototheca moriformis (UTEX 1435) codon usage. A representative transforming construct and the sequence of the FATB enzymes is provided in SEQ ID NO: 38, using CcrasFATB1 as an example. The new thioesterases were synthesized with a modified transit peptide from Chlorella protothecoides (Cp) (SEQ ID NO: 40) in place of the native transit peptide. The modified transit peptide derived from the CpSAD1 gene, “CpSAD1tp_trimmed”, was synthesized as an in-frame, N-terminal fusion to the FATB thioesterases in place of the native transit peptide.
Transgenic strains were generated via transformation of the base strain S7485 with a construct encoding 1 of the 12 FatB thioesterases. The construct pSZ5342/D4219 encoding CcrasFATB1 is shown as an example, but identical methods were used to generate each of the remaining 11 constructs encoding the different respective thioesterases. Construct pSZ5342 can be written as THI4A_5′::CrTUB2-ScSUC2-PmPGH:PmSAD2-2ver3-CpSAD1tp_trmd:CcrasFATB1-CvNR-THI4A_3′. The relevant restriction sites in the construct from 5′-3′, BspQ1, KpnI, BamHI, EcoRV, SpeI, XhoI, SacI, BspQ1, respectively, are indicated in lowercase, bold, and underlined. BspQ1 sites delimit the 5′ and 3′ ends of the transforming DNA. Bold, lowercase sequences at the 5′ and 3′ end of the construct represent genomic DNA from UTEX 1435 that target integration to the THI4A locus via homologous recombination. Proceeding in the 5′ to 3′ direction, the selection cassette has the C. reinhardtii β-tubulin promoter driving expression of the S. cerevisiae gene SUC2 (conferring the ability to grow on sucrose) and the P.moriformis PGH gene 3′ UTR. The promoter is indicated by lowercase, boxed text. The initiator ATG and terminator TGA for ScSUC2 are indicated by bold, uppercase italics, while the coding region is indicated with lowercase italics. The 3′ UTR is indicated by lowercase underlined text. The spacer region between the two cassettes is indicated by upper case text. The second cassette containing the codon optimized CcrasFATB1 gene from Cuphea crassiflora fused to the heterologous C. protothecoides SAD1 plastid-targeting transit peptide, CpSAD1tp_trimmed, is driven by the P.moriformis SAD2-2ver3 pH5-responsive promoter and has the Chlorella vulgaris Nitrate Reductase (NR) gene 3′ UTR. In this cassette, the PmSAD2-2ver3 promoter is indicated by lowercase, boxed text. The initiator ATG and terminator TGA for the CcrasFATB1 gene are indicated in bold, uppercase italics, while the coding region is indicated by lowercase italics. The 3′ UTR is indicated by lowercase underlined text.
The sequence for all of the thioesterase constructs is identical with the exception of the encoded thioesterase. The full sequence for pSZ5342/D4219 integrating construct (SEQ ID NO: 38) is provided.
Constructs encoding heterologous FATB genes were transformed into a high-lipid-producing Prototheca strain and selected for the ability to grow on sucrose. Transformations, cell culture, lipid production and fatty acid analysis were all carried out as in WO2013/158938. Multiple transformations were performed. The fatty acid profiles of the strain with the highest C10 (for the first 6 genes listed), or C12 production (for the remaining genes) is reported in Table 8.
The six thioesterases from the Lythraceae cluster all display specificity towards C10:0 fatty acids: CcrasFATB1, which exhibits 4% C10:0 and 1% C12:0 fatty acid levels; CkoeFATB3, which exhibits 9% C10:0 and 2% C12:0 fatty acid levels; CleptFATB1, which exhibits 6% C10:0 and 1% C12:0 fatty acid levels; CangFATB1, which exhibits 4% C10:0 and 1% C12:0 fatty acid levels; CllaFATB1, which exhibits 9% C10:0 and 1% C12:0 fatty acid levels; and, ClopFATB1, which exhibits 7% C10:0 and 1% C12:0 fatty acid levels.
SalFATB1 and LbeFATB1, both of the Lauraceae family, exhibit substantial activity towards C12:0 fatty acids.
EXAMPLE 3 FATB Deletion Mutants of Lauraceae FATB GenesTransforming vectors for deletion variants, of SalFATB1, and LbeFATB1, known respectively as SalFATB 1 a and LbeFATB1a, were synthesized, using the expression cassette and transit-peptide described in Example 2. The deletion variants had deletions in the region corresponding to amino acids 66-98 of the SalFATB2 gene (SEQ ID NO: 8). The constructs were codon-optimized to reflect UTEX 1435 codon usage. Transformations, cell culture, lipid production and fatty acid analysis were carried out as in Example 2. Constructs encoding heterologous FATB genes were transformed into a Prototheca moriformis strain and selected for the ability to grow on sucrose. The results for the two novel FATB thioesterases are displayed in Table 9.
SalFATB1 and LbeFATB1, both of the Lauraceae family, exhibit substantial activity towards C12:0 fatty acids. SalFATB1a, which has a deletion of the 32 amino acids LFAVITTIFSVAEKQWTNLEWKPKPKPRLPQL (SEQ ID NO: 47), produced up to 15% C12:0 compared to 7% produced by the wild-type SalFATB1. The mean C12:0 level in SalFATB1a was 8.3% compared to 3.7% in SalFATB1, demonstrating a greater than 2-fold increase in activity upon deletion of the 32 amino acids. LbeFATB1a, which had a deletion of the 28 amino acids LLTVITTIFSAAEKQWTNLERKPKPPHL (SEQ ID NO: 48), produced up to 28% C12:0 compared to 11% produced by the wild-type LbeFATB1. The mean C12:0 level in LbeFATB1a is 17.2% compared to just 5.7% in LbeFATB1, demonstrating a greater than 3.0-fold increase in activity upon deletion of the 28 amino acids. The data suggest that deletion of those amino acids significantly improves (e.g., by 2-3 fold) the C12 activity of two other Lauraceae family thioesterases, SalFATB1 and LbeFATB1.
EXAMPLE 4 Additional Deletion Mutants from FATB Genes from LythraceaeP. moriformis was transformed with additional deletion mutants of Lythraceae FATB genes above for Lauraceae FATB genes. Two deletion mutants were identified that showed elevated midchain (C8-14) fatty acid levels in cell-oil extracted from the microalga relative an equivalent transformation lacking the deletion. These are listed in Table 9, above in which they appear as CpauFATB1Δ28 and ChFATB2Δ27. Fatty acid profiles obtained in the P. moriformis model system are reported below in Table 10. ChFATB2Δ27 demonstrated an increase in C8 and C10 fatty acids when compared to the wild-type, elaborating an average of 3.8% C8:0 and 11.5% C10:0 compared to 2.7% C8:0 and 8.0% C10:0, respectively. CpauFATB1Δ28 demonstrates an increase in C10, C12 and C14 fatty acids when compared to the wild-type, elaborating an average of 7.6% C10:0 compared to 4.1% C10:0, respectively.
In the example below, we demonstrate the ability of modifying the enzyme specificity of a FATA thioesterase originally isolated from Brassica napus (BnOTE, accession CAA52070), by site directed mutagenesis targeting two amino acids positions (D124 and D209).
To determine the impact of each amino acid substitution on the enzyme specificity of the BnOTE, the wild-type and the mutant BnOTE genes were cloned into a vector enabling expression within the lower palmitate P. moriformis strain S8588. The Saccharomyces carlsbergensis MEL1 gene (Accession no: AAA34770) was utilized as the selectable marker to introduce the wild-type and mutant BnOTE genes into FAD2-2 locus of P. moriformis strain S8588 by homologous recombination using previously described transformation methods (biolistics). The constructs that have been expressed in S8588 are listed in Table 11. S8588 is a recombinant P. moriformis strain having a FATA knockout and expressing an exogenous SUC2 gene and an exogenous P. moriformis KASII gene in the FATA locus. FATA knockouts that express sucrose invertase and/or KASII are described in co-owned applications WO2012/106560, WO2013/158938, WO2015/051319 and their respective priority applications thereof, all of which are herein incorporated by reference.
Construct pSZ6315: FAD2-2::PmHXT1-ScarMEL1-PmPGK:PmSAD2-2 V3-CpSADtp-BnOTE-PmSAD2-1 utr::FAD2-2
The sequence of the pSZ6315 transforming DNA is provided in SEQ ID NO: 57. Relevant restriction sites in pSZ6315 are indicated in lowercase, bold and underlining and are 5′-3′ SgrAI, Kpn I, SnaBI, AvrII, SpeI, AscI, ClaI, Sac I, SbfI, respectively. SgrAI and SbfI sites delimit the 5′ and 3′ ends of the transforming DNA. Bold, lowercase sequences represent FAD2-2 genomic DNA that permit targeted integration at FAD2-2 locus via homologous recombination. Proceeding in the 5′ to 3′ direction, the P. moriformis HXT1 promoter driving the expression of the Saccharomyces carlsbergensis MEL1 gene is indicated by boxed text. The initiator ATG and terminator TGA for MEL1 gene are indicated by uppercase, bold italics while the coding region is indicated in lowercase italics. The P. moriformis PGK 3′ UTR is indicated by lowercase underlined text followed by the P. moriformis SAD2-2 V3 promoter, indicated by boxed italics text. The Initiator ATG and terminator TGA codons of the wild-type BnOTE are indicated by uppercase, bold italics, while the remainder of the coding region is indicated by bold italics. The three-nucleotide codon corresponding to the target two amino acids, D124 and D209, are double underlined. The P. moriformis SAD2-1 3′UTR is again indicated by lowercase underlined text followed by the FAD2-2 genomic region indicated by bold, lowercase text.
Construct pSZ6316: FAD2-2::PmHXT1-ScarMEL1-PmPGK:PmSAD2-2 V3-CpSADtp-BnOTE (D124A)-PmSAD2-1 utr::FAD2-2
The sequence of the pSZ6316 transforming DNA is same as pSZ6315 except the D124A point mutation, the BnOTE D124A DNA sequence is provided in SEQ ID NO: 58.
Construct pSZ6317: FAD2-2::PmHXT1-ScarMEL1-PmPGK:PmSAD2-2 V3-CpSADtp-BnOTE (D209A)-PmSAD2-1 utr::FAD2-2
The sequence of the pSZ6317 transforming DNA is same as pSZ6315 except the D209A point mutation, the BnOTE D209A DNA sequence is provided in SEQ ID NO: 59.
Construct pSZ6318: FAD2-2::PmHXT1-ScarMEL1-PmPGK:PmSAD2-2 V3-CpSADtp-BnOTE (D124A, D209A)-PmSAD2-1 utr::FAD2-2
The sequence of the pSZ6318 transforming DNA is same as pSZ6315 except two point mutations, D124A and D209A, the BnOTE (D124A, D209A) DNA sequence is provided in SEQ ID NO:60.
ResultsThe DNA constructs containing the wild-type and mutant BnOTE genes were transformed into the low palmitate parental strain S8588, primary transformants were clonally purified and grown under standard lipid production conditions at pH5.0. The resulting profiles from representative clones arising from transformations with pSZ6315, pSZ6316, pSZ6317, and pSZ6318 into S8588 are shown in Table 12. The parental strain S8588 produces 5.4% C18:0, when transformed with the DNA cassette expressing wild-type BnOTE, the transgenic lines produce approximately 11% C18:0. The BnOTE mutant (D124A) increased the amount of C18:0 by at least 2 fold compared to the wild-type protein. In contrast, the BnOTE D209A mutation appears to have no impact on the enzyme activity/specificity of the BnOTE thioesterase. Finally, expression of the BnOTE (D124A, D209A) resulted in very similar fatty acid profile to what we observed in the transformants from S8588 expressing BnOTE (S124A), again indicating that D209A has no significant impact on the enzyme activity.
It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes.
Informal Sequence Listing
Claims
1. A cDNA or nucleic acid construct comprising a polynucleotide sequence encoding a heterologous regulatory element and a FatB acyl-ACP thioesterase gene operable to produce an altered fatty acid profile in an oil produced by a cell expressing the nucleic acid construct, wherein the FatB gene expresses a protein having an amino acid sequence having at least 65% identity to SEQ ID NO: 40 or SEQ ID NO: 42.
2. The cDNA or nucleic acid construct of claim 1, wherein the acyl-ACP thioesterase coding sequence comprises at least 65% identity to SEQ ID NO: 44 or any equivalent sequences by virtue of the degeneracy of the genetic code.
3. (canceled)
4. The nucleic acid construct of claim 1, further comprising a polynucleotide encoding a plastid targeting peptide with at least 65% identity to SEQ ID NO: 37.
5. (canceled)
6. A host cell capable of expressing the cDNA or nucleic acid construct of claim 1 so as to produce a triglyceride oil having an altered composition relative to a control cell without the construct, the oil optionally having an increase in C8-C12 fatty acids.
7. A host cell capable of expressing the cDNA or nucleic acid construct of claim 1 so as to produce a triglyceride oil having an altered composition relative to a control cell without the construct, the oil optionally having an increase in C10 and C12 fatty acids.
8. The host cell of claim 6, wherein the host cell is selected from the group consisting of a plant cell, a microbial cell, and a microalgal cell.
9. A method of producing a recombinant cell that produces an altered fatty acid profile, the method comprising transforming a cell with a cDNA or nucleic acid construct of claim 1.
10. A host cell produced by the method of claim 9.
11. The host cell of claim 10, wherein the host cell is selected from the group consisting of a plant cell, a microbial cell, and a microalgal cell.
12. A method for producing an oil or oil-derived product, the method comprising cultivating a host cell of claim 6 and extracting oil produced thereby, optionally wherein the cultivation is by heterotrophic growth on sugar.
13. The method of claim 12, further comprising producing a fatty acid, fuel, chemical, food, or other oil-derived product from the oil.
14. (canceled)
15. An oil produced by the method of claim 12, optionally having a fatty acid profile comprising at least 20% C8, C10, C12, C14, C16 or C18 fatty acids.
16. The oil of claim 15, wherein the oil is produced by a microalgae, has a microalgal sterol profile, and optionally, lacks C24-alpha sterols.
17. (canceled)
18. A method for producing an oil, the method comprising:
- (a) providing a plastidic, oleaginous cell, optionally a microbial cell, the cell expressing a functional, acyl-ACP thioesterase gene encoded by a FATB gene having a deletion mutation in a region corresponding to the region coding for amino acids 66-98 of SEQ ID NO: 8;
- (b) cultivating the cell to produce a cell-oil; and
- (c) isolating the cell-oil from the cell.
19. The method of claim 17, wherein the cell-oil is enriched in C12 due to the deletion.
20. The method of claim 18 wherein the FATB gene encodes a protein with at least 65% sequence identity to SEQ ID NO: 42.
21. (canceled)
22.-38. (canceled)
39. The oil produced by the method of claim 19, wherein the fatty acid profile of the cell-oil comprises at least 5% C12 fatty acids.
40. The oil produced by the method of claim 39, wherein the fatty acid profile of the cell-oil comprises at least 10% C12 fatty acids.
41. The oil produced by the method of claim 40, wherein the fatty acid profile of the cell-oil comprises at least 15% C12 fatty acids.
Type: Application
Filed: Nov 9, 2018
Publication Date: Jun 27, 2019
Inventors: Jason Casolari (Palo Alto, CA), George N. Rudenko (Mountain View, CA), Scott Franklin (Woodside, CA), Xinhua Zhao (Dublin, CA)
Application Number: 16/185,705
