TaFlo2-A1, an ortholog of rice Flo2, is associated with thousand grain weight in bread wheat (Triticum aestivum L.)

Muhammad Sajjad, Xiaoling Ma, Sultan Habibullah Khan, Muhammad Shoaib, Yanhong Song, Wenlong Yang, Aimin Zhang, Dongcheng Liu

The Flo2 gene is a member of a conserved gene family in plants. This gene has been found to be related to thousand grain weight (TGW) in rice. Its orthologs in hexaploid wheat were cloned, and the haplotype variation in TaFlo2-A1 was tested for association with TGW. The cloned sequences of TaFlo2-A1, TaFlo2-B1 and TaFlo2-D1 contained 23, 23 and 24 exons, respectively. The deduced proteins of TaFlo2-A1 (1734 aa), TaFlo2-B1 (1698 aa) and TaFlo2-D1 (1682 aa) were highly similar (>94%) and exhibited >77% similarity with the rice FLO2 protein. Like the rice FLO2 protein, four tetratricopeptide repeat (TPR) motifs were observed in the deduced TaFLO2 protein. An 8-bp InDel (-10 to -17 bp) in the promoter region and five SNPs in first intron of TaFlo2-A1 together formed two haplotypes, TaFlo2-A1a and TaFlo2-A1b, in bread wheat. TaFlo2 was located on homeologous group 2 chromosomes. TaFlo2-A1 was inferred to be located on deletion bin '2AL1-0.85-1.00'. The TaFlo2-A1 haplotypes were characterized in the Chinese Micro Core Collection (MCC) and Pakistani wheat collection using the molecular marker TaFlo2-Indel8. TaFlo2-A1 was found to be associated with TGW but not with grain number per spike (GpS) in both the MCC and Pakistani wheat collections. The frequency of TaFlo2-A1b (positive haplotype) was low in commercial wheat cultivars; thus this haplotype can be selected to improve grain weight without negatively affecting GpS. The expression level of TaFlo2-A1 in developing grains at 5 DAF (days after flowering) was positively correlated with TGW in cultivars carrying the positive haplotype. This study will likely lead to additional investigations to understand the regulatory mechanism of the Flo2 gene in hexaploid wheat. Furthermore, the newly developed molecular marker 'TaFlo2-InDel8' could be incorporated into the kit of wheat breeders for use in marker-assisted selection.