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 cont ent and composition by altering the activity of a specific isoform (SB EI) of starch-branching enzyme. There are several pleiotropic conseque nces of homozygosity for a mutant allele at the r locus, including see d wrinkling, and increased lipid and sugar concentrations that are tho ught 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 exp ression, apparently through the specific destabilization of legumin mR NAs in the high-sugar environment of the developing rr seed; the amoun ts of vicilin and convicilin mRNAs are unaffected. Other wrinkled-seed ed mutants have been identified that perturb starch synthesis and resu lt in elevated sugar levels in developing seeds; these include rb, a m utation in one of the structural genes for ADPglucose pyrophosphorylas e. The recent production of a series of near-isogenic mutant and doubl e mutant backcross lines for r and rb, and of near-isogenic lines cont aining 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 ex pression of legumin and vicilin genes in a range of different near-iso genic lines with different patterns of carbohydrate metabolism. We rep ort and discuss here analyses of legumin and vicilin deposition in pea genotypes RRRbRb (wild-type round-seeded), rrRbRb, RRrbrb, rrrbrb (al l wrinkled-seeded), the homozygous wrinkled-seeded mutants rug-3, rug- 4 and rug-5 and the round-seeded low-amylose mutant lam.