Natural variation of TaGASR7-A1 affects grain length in common wheat under multiple cultivation conditions

GASR7 is a member of Snakin/GASA gene family in higher plants and has been found associated with grain length (GL) in rice and wheat under normal growth conditions. Here, we report the characterization of three distinct TaGASR7 homoeologs (TaGASR7-A1, TaGASR7-B1 and TaGASR7-D1) in common wheat and their deduced proteins and haplotype variation. TaGASR7 homoeologs were located on wheat group 7 chromosomes. Compared with previously characterized Snakin/GASA members, the central region in deduced TaGASR7 proteins and their orthologs was unique in containing a polyglycine tract. Through analyzing longer genomic sequence, more nucleotide differences were found for the two previously reported major haplotypes (H1c and H1g) of TaGASR7-A1. In contrast, no haplotype variation was detected for TaGASR7-B1 and TaGASR7-D1 in the 94 elite common wheat varieties examined. H1c, but not H1g, tended to associate with larger GL values in nine cultivation environments differing in water and nutrient application. However, the positive association between H1c and other grain traits (grain weight and yield) was affected by cultivation environment. Both H1c- and H1g-type alleles were more highly expressed in the unfertilized caryopses and those collected at 5 days after flowering (DAF). Interestingly, at 5 DAF, the expression level of H1c-type alleles was significantly lower than that of H1g-type alleles. By combining our data with those published previously, we suggest that TaGASR7-A1 is mainly a genetic determinant of GL in wheat with pleiotropic effects on grain weight and yield. Potential mechanism underlying TaGASR7-A1 function and its utility in enhancing genetic and breeding studies of wheat grain morphometric and yield traits are discussed.