Abstract: The present invention includes a transgenic plant containing a GDP-mannose pyrophosphorylase gene. A pathway for AsA biosynthesis that features GDP-mannose and L-galactose has recently been proposed for plants. A collection of AsA-deficient mutants of Arabidopsis thaliana that are valuable tools for testing of a novel AsA biosynthetic pathway have been isolated. The best characterized of these mutants (vtc1-vitamin c) contains ˜25% of wildtype AsA and is defective in AsA biosynthesis. Using a combination of biochemical, molecular, and genetic techniques, it has been conclusively demonstrated that the VTC1 locus encodes GDP-mannose pyrophosphorylase (mannose-1-P guanyltransferase). This enzyme provides GDP-mannose, which is used for cell wall carbohydrate biosynthesis and protein glycosylation, as well as for AsA biosynthesis.

Abstract: Disclosed are methods of increasing exogenous protein expression in a cell or a transgenic plant. Constructs, i.e., vectors, DNA fusions and polynucleotides, for use in conjunction with the methods to cause increased exogenous protein expression are also disclosed. These constructs generally include intron 1 and/or intron 2 of the PAT1 gene. Additionally disclosed are cells, including recombinant cells, and plant lines transformed with the described constructs. In particular, a cultivated, transgenic food plant, the genome of which has been augmented through the genomic introduction of a preselected exogenous protein gene not found in the genome of non-transformed parentage of the plant is described. Also described are seed, progeny and cells of the described transgenic food plant.