Function of TaGW2-6A and its effect on grain weight in wheat (Triticum aestivum L.)

Grain weight is an important factor contributing to grain yield in wheat. Markers closely linked to grain weight could be used in marker-assisted selection (MAS) to accelerate the wheat breeding process. In this paper, a second backcross recombinant inbred line (BC2F4) population, a recombinant inbred line (RIL) population, and one natural population were used to study the relationship between allelic variants of the grain weight gene TaGW2-6A and grain weight, width, and length with the goal of verifying the feasibility using the functional marker Hap-6A-P1/P2 in MAS. The differences in average grain weight, width, and length between haplotypes Hap-6A-G and Hap-6A-A were 8.09 g, 0.22 mm, and 0.38 mm, respectively, in the BC2F4 population; 4.01 g, 0.11 mm, and 0.10 mm in the RIL population; and 3.95 g, 0.10 mm, and 0.20 mm in the natural population. All the differences were significant. Sequencing results of the products of second round PCR indicated that a 167 bp TaqI restriction fragment had been generated from small-grain-size materials because of three TaqI restriction sites (TCGA). However, the large-grain-size variant generated a 218 bp fragment due to a single-nucleotide mutation (SNP) (TCGA -> TCGG) at the third site. TaGW2-6A expression levels were negative with respect to grain width, length, and weight. For this reason, Hap-6A-G was considered a superior allele. These results contradict those of a previous study, which showed Hap-6A-A to be significantly associated with wider grain and higher grain weight.