Genetic variability of Hin genes in selected barley germplasm and potential implications for grain texture

Abstract

Grain hardness (texture) in barley is a commercially important trait, associated with water-uptake during the steeping phase of malting, quantified by measuring endosperm hardness. Hordoindolines are seed proteins of barley, related to the wheat puroindoline proteins. The Hordoindoline genes Hina, Hinb-1 and Hinb-2 are orthologs of wheat Pin genes. The information on contributions of Hin genes to barley grain hardness is limited and somewhat ambiguous. Hence this study aimed to investigate the genetic diversity of Hin genes in 12 Australian barley cultivars and 14 landraces originating from geographic centers of diversity. The grain hardness was determined by the Single Kernel Characterisation System (SKCS) and ranged between 24.2–78.5 SKCS units for cultivars and 48.7–94.4 SKCS units for landraces. Hin gene amplifications and DNA sequencing indicated notable genetic diversity, with seven Hina, six Hinb-1 alleles and eight Hinb-2 alleles detected. Some of the SNPs led to substitutions at the potentially functionally important tryptophan rich domain and certain basic and hydrophobic residues in the putative proteins. A novel Hinb-1 allele with an insertion at nucleotide position 210, leading to a frame-shift mutation, was discovered in landrace L400211 from Ethiopia that had a high SKCS hardness value, indicating harder grain. The study suggests that Hin gene variations may contribute to barley grain hardness, and selection of certain alleles may be useful for breeding for varying barley grain textures.