A glycine to serine change in puroindoline b is associated with wheat grain hardness and low levels of starch-surface friabilin

Abstract

The quantitative level of friabilin 15-kDa protein present on the surface of water-washed starch is highly correlated with wheat grain softness. Friabilin is composed primarily, if not exclusively, of the proteins 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 chromosomal location of the Hardness gene. We report here a glycine to serine 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 properties of puroindolines. No recombination was observed between the serine puroindoline-b mutation, hard grain texture and low levels of starch surface friabilin among a set of 83 homozygous 5D recombinant lines derived from the soft-textured variety 'Chinese Spring' and the substitution line 'Chinese Spring' containing the 5D chromosome of the hard-textured variety 'Cheyenne'. The sequence change reported here may adversely affect the lipid-binding properties of puroindoline-b and so effect hard grain texture. The results suggest that grain hardness results from puroindoline-b functionality such that the Hardness gene is a direct manifestation of puroindoline structure. We are suggesting the tentative molecular marker loci designations of Pinb-D1a and Pinb-D1b for the glycine and serine puroindoline-b types, respectively.