Epigenetic modification contributes to the expression divergence of three TaEXPAl homoeologs in hexaploid wheat (Triticum aestivum)

摘要

Common wheat is a hexaploid species with most of the genes present as triplicate homoeo-logs. Expression divergences of homoeologs are frequently observed in wheat, as well as in other polyploid plants. However, the mechanisms underlying this phenomenon are poorly understood. Expansin genes play important roles in the regulation of cell size, as well as organ size. We found that all three TaEXPAl homoeologs were silenced in seedling roots. In seedling leaves, TaEXPA1-A and TaEXPAl-D were expressed, but TaEXPAl-B was silenced. Further analysis revealed that silencing of TaEXPA1-B in leaves occurred after the formation of the hexaploid. Chromatin immunoprecipitation assays revealed that the transcriptional silencing of three TaEXPAl homoeologs in roots was correlated with an increased level of H3K9 dimethylation and decreased levels of H3K4 trimethylation and H3K9 acetylation. Reactivation of TaEXPAI-A and TaEXPA1-D expression in leaves was correlated with increased levels of H3K4 trimethylation andH3K9 acetylation, and decreased levels of H3K9 dimethylation in their promoters, respectively. Moreover, a higher level of cytosine methylation was detected in the promoter region of TaEXPA1-B, which may contribute to its silencing in leaves. We demonstrated that epigenetic modifications contribute to the expression divergence of three TaEXPAl homoeologs during wheat development.