Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2002
Publication Date: 9/19/2002
Interpretive Summary: The texture of endosperm has an impact on the utility of grain. Knowing the genetics and biochemistry for hard and soft wheat facilitates breeding efforts and studies of end-use quality. Puroindoline proteins in wheat were thought to be the primary determinant of endosperm texture (hard wheat or soft wheat). There has been controversy about whether puroindolines actually affect grain texture or are merely a compound associated with hardness or softness. In this research, a hard wheat with a mutation in one of its puroindoline proteins (pinB), thought to be the cause of hardness, was used as the subject for experimental transformation. A non-mutated, soft version of pinB was inserted into the hard wheat. Analysis showed that the soft type puroindoline was successfully expressed and that hard-textured grain was now very soft-textured, due only to the presence of the puroindoline protein. This shows unequivocally that puroindolines are, indeed, the cause of hard or soft wheat and that they do represent the Ha (Hardness) gene.
Technical Abstract: Wheat grain hardness is a major factor in wheat end-product quality. Grain hardness in wheat affects such parameters as milling yield, starch damage and baking properties. A single locus determines whether wheat is hard or soft textured. This locus, termed Hardness (Ha), resides on the short arm of chromosome 5D. Sequence alterations in the tryptophan-rich proteins puroindoline a and b (PINA and PINB) are inseparably linked to hard textured grain, but their role in endosperm texture has been controversial. Here, we show that the pinB-D1b alteration, common in hard textured wheats, can be complemented by the expression of wild-type pinB-D1a in transformed plants. Transgenic wheat seeds expressing wild-type pinB were soft in phenotype, having greatly increased friabilin levels, and greatly decreased kernel hardness and damaged starch. These results indicate that the pinB-D1b alteration is most likely the causative Ha mutation in the majority of hard wheats.