Molecular genetics of puroindolines and related genes: allelic diversity in wheat and other grasses.

The hardness or texture of cereal grains is a primary determinant of their technological and processing quality. Among members of the Triticeae, most notably wheat, much of the variation in texture is controlled by a single locus comprised of the Puroindoline a, Puroindoline b and Grain Softness Protein-1 (Gsp-1) genes. Puroindolines confer the three major texture classes of soft and hard common wheat and the very hard durum wheat. The protein products of these genes interact with lipids and are associated with the surface of isolated starch (as a protein fraction known as 'friabilin'). During the past ten years a great diversity of alleles of both Puroindoline genes have been discovered and significant advances made in understanding the relationship between the gene presence/absence, sequence polymorphism and texture of cereal grains. Efforts have also focussed on Puroindoline and Gsp-1 genes in diploid progenitors, other Triticeae grasses and synthetic wheats in order to understand the evolution of this gene family and find potentially useful variants. The puroindoline homologues in other cereals such as rye and barley are also receiving attention. This work summarises new developments in molecular genetics of puroindolines in wheat and related Triticeae grasses, and the related genes in other cereals.