The effect of modifying carbohydrate metabolism on seed protein gene expression in peas

Mutations at the r locus in peas (Pisum sativum L.) affect starch content and composition by altering the activity of a specific isoform (SBEI) of starch-branching enzyme. There are several pleiotropic consequences of homozygosity for a mutant allele at the r locus, including seed wrinkling, and increased lipid and sugar concentrations that are thought to be, at least in part, a consequence of the re-partitioning of carbon that is incorporated into starch in the wild-type line. Mutant alleles at the r locus also have an effect on storage protein gene expression, apparently through the specific destabilization of legumin mRNAs in the high-sugar environment of the developing rr seed; the amounts of vicilin and convicilin mRNAs are unaffected. Other wrinkled-seeded mutants have been identified that perturb starch synthesis and result in elevated sugar levels in developing seeds; these include rb, a mutation in one of the structural genes for ADPglucose pyrophosphorylase. The recent production of a series of near-isogenic mutant and double mutant backcross lines for r and rb, and of near-isogenic lines containing four additional mutations that influence starch synthesis (lam, rug-3, rug-4 and rug-5, defective in a granule-bound starch synthase, plastidial phosphoglucomutase, sucrose synthase and a soluble starch synthase, respectively) has provided the opportunity to examine the expression of legumin and vicilin genes in a range of different near-isogenic lines with different patterns of carbohydrate metabolism. We report and discuss here analyses of legumin and vicilin deposition in pea genotypes RRRbRb (wild-type round-seeded), rrRbRb, RRrbrb, rrrbrb (all wrinkled-seeded), the homozygous wrinkled-seeded mutants rug-3, rug-4 and rug-5 and the round-seeded low-amylose mutant lam.