Abstract
Background: The bHLH transcription factor SD6 regulates rice seed dormancy. However, sequence variants of wheat SD6 homologs and their roles in seed dormancy remain unknown. Results: 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 TaSD6-7AHapII 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. Conclusion: Overall, this study provides novel genetic resources and molecular markers for improving PHS resistance of modern wheat varieties.