Influence of the Genes at the Ha Loci on Hardness in Wheat

Grain hardness is a prime determinant of wheat quality. Variations in grain hardness directly affect milling properties and end-use quality of wheat. It is now well established that puroindoline (Pin) genes located on the Ha locus control the grain hardness. Grain softness protein-1 gene (GSP-1) at the same locus may also play minor role in grain hardness. Several mutant alleles of Pina and Pinb have been reported in recent years. The presence of certain combinations of specific Pina and Pinb alleles is believed to determine grain softness/hardness. However, the variation in grain hardness among the different cultivars containing identical Pina and Pinb alleles hasn’t yet been explained. To further understand grain hardness we have analysed transcript data of 32 worldwide wheat varieties at two stages of seed development; 14 and 30, days post anthesis (DPA). Differential patterns of Pina, Pinb and GSP-1 gene expression were observed in different varieties. Overall, higher expression of Pina than Pinb was observed in most of the varieties except six varieties which showed quite discrete patterns of expression and displayed hard texture without the presence of any mutant allele. Reduced expression of Pinb and GSP-1 was observed in Pina-D1b mutants whereas in Pinb-D1b mutants increased expression of Pina and GSP-1 was observed. Statistical analysis showed that gene expression at 14 DPA can explain hardness better than gene expression at 30 DPA. Results of this study indicate that different patterns of Pina and Pinb expression may have a significant impact on variation in wheat grain hardness.