Identification and genetic mapping of variant forms of puroindoline b expressed in developing wheat grain

Transcripts encoding three novel variant forms of puroindoline b have been identified in developing seeds of wheat. These show 57-60% sequence identity with the wild type form of Pin b but all lack one of the three tryptophan residues present in the “tryptophan loop” region of the wild type protein. Counts of ESTs and array analysis indicate that the transcripts encoding variant forms of Pin b are about an order of magnitude less abundant than those encoding wild type Pin b while array analysis also shows that expression of the variant form 1 declines more rapidly than that of the wild type form during the later stages of grain development. The gene(s) encoding variant form 1, named Pinb-A2, were mapped to the long arm of chromosome 7A of bread wheat where they show linkage to novel QTLs for hardness which have been identified in two doubled haploid populations derived from crosses between hard parental cultivars (Shamrock × Shango, Malacca × Charger).