Natural variation and functional analysis of TaSD6 genes regulating seed dormancy in common wheat

The bHLH transcription factor SD6 regulates rice seed dormancy. However, sequence variants of wheat SD6 homologs and their roles in seed dormancy remain unknown.

Here, we cloned three wheat homologous genes of SD6 (named TaSD6-7A, TaSD6-7B, and TaSD6-7D), and found that TaSD6-7A had abundant sequence variations, while TaSD6-7B and TaSD6-7D had no variation. Based on sequence variations in the promoter and coding regions of TaSD6-7A, we developed three molecular markers and verified their associations with seed dormancy in 160 wheat varieties. We further confirmed that the TaSD6-7 A + 1307-T allele positively regulated seed dormancy, but had no adverse effects on other important agronomic traits. Resequencing and phenotypic data indicated that the favorable haplotype TaSD6-7A^HapII associated with high dormancy level was more common in landraces than in modern varieties. Additionally, we demonstrated the pyramid effects of TaSD6-7A with known dormancy-related genes in enhancing seed dormancy.

Overall, this study provides novel genetic resources and molecular markers for improving PHS resistance of modern wheat varieties.