A GLYCINE TO SERINE CHANGE IN PUROINDOLINE-B IS ASSOCIATED WITH WHEAT-GRAIN HARDNESS AND LOW-LEVELS OF STARCH-SURFACE FRIABILIN

The quantitative level of friabilin 15-kDa protein present on the surf ace of water-washed starch is highly correlated with wheat grain softn ess. Friabilin is composed primarily, if not exclusively, of the prote ins puroindoline a and b. The transcript levels of these two proteins are similar among hard and soft wheat varieties, and the expression of both is controlled by the short arm of chromosome 5D, also the chromo somal location of the Hardness gene. We report here a glycine to serin e sequence change in puroindoline b associated with hard grain texture . This amino acid change results from a single nucleotide mutation and resides in a region thought to be important for the lipid-binding pro perties of puroindolines. No recombination was observed between the se rine puroindoline-b mutation, hard grain texture and low levels of sta rch surface friabilin among a set of 83 homozygous 5D recombinant line s derived from the soft-textured variety 'Chinese Spring' and the subs titution line 'Chinese Spring' containing the 5D chromosome of the har d-textured variety 'Cheyenne'. The sequence change reported here may a dversely affect the lipid-binding properties of puroindoline-b and so effect hard grain texture. The results suggest that grain hardness res ults from puroindoline-b functionality such that the Hardness gene is a direct manifestation of puroindoline structure. We are suggesting th e tentative molecular marker loci designations of Pinb-D1a and Pinb-D1 b for the glycine and serine puroindoline-b types, respectively.