A leucine to proline mutation in puroindoline b is frequently present in hard wheats from Northern Europe

Endosperm hardness in wheat (Triticum aestivum L.) is determined by one major genetic factor, the Hardness (Ha) gene on the short arm of chromosome 5D. Grain hardness has previously been reported to result from either a failure to express puroindoline a (Pina-D1b) or a glycine to serine mutation at position 46 in puroindoline b (Pinb-D1b). In this study, which involves a large survey of 343 wheat genotypes of mostly Northern European origin, we report two new mutations in puroindoline b associated with hard endosperm. These were characterized as involving a leucine to proline change at position 60 (Pinb-D1c), and a tryptophan to arginine change at position 44 (Pinb-D1d), respectively. While the former seems to be widely distributed in germplasm around the world, the latter was only found in three winter wheats from Sweden and Netherlands. As discussed in the paper, the three known mutations in puroindoline b can be considered ''loss-of-function" mutations (i.e. soft to hard), and structural analysis may serve to predict that their dramatic effect on wheat grain texture is a result of reduced lipid-binding ability.