Gsp-1 genes comprise a multigene family in wheat that exhibits a unique combination of sequence diversity yet conservation

While the commercially important trait of grain hardness in wheat is largely determined by the puroindoline proteins, a number of studies suggest additional loci, and a role for the grain softness protein-1 (GSP-1), encoded by the gene Gsp-1 tightly linked to the puroindoline genes, remains ambiguous. To investigate their role individual Gsp-1 genes were cloned from several accessions of durum, diploid and hexaploid wheat, rather than sequencing of genomic DNA PCR products. Analysis of clones identified >1 restriction fragment length polymorphisms (RFLPs) in some 2n progenitors, >2 RFLP types in several durums and >3 in common wheat. DNA sequencing identified 30 different Gsp-1 haplotypes from various 2n, 4n and 6n wheats, exhibiting extensive single nucleotide polymorphisms (SNPs) and a 3-base deletion, all but three haplotypes being novel. Shared SNPs between various diploids, indicated an ancient origin of this gene family, but certain aspects were unique to durums, and existence of multigenes in at least some genomes was confirmed through single plant analysis of select accessions of Aegilops speltoides, durum and common wheat. Most interestingly, despite the great sequence diversity, the functionally important amino acids involved in lipid binding, i.e., the 10 cysteines and two tryptophans, were retained in all putative proteins. The results suggest that these genes may be functionally important, particularly in durums which lack puroindolines, and may have major roles in plant defence and only a minor influence on grain texture.