Epigenetic modification contributes to the expression divergence of three Ta EXPA1 homoeologs in hexaploid wheat ( Triticum aestivum).

Common wheat is a hexaploid species with most of the genes present as triplicate homoeologs. 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 Ta EXPA1 homoeologs were silenced in seedling roots. In seedling leaves, Ta EXPA1- A and Ta EXPA1- D were expressed, but Ta EXPA1- B was silenced. Further analysis revealed that silencing of Ta EXPA1- B in leaves occurred after the formation of the hexaploid., Chromatin immunoprecipitation assays revealed that the transcriptional silencing of three Ta EXPA1 homoeologs in roots was correlated with an increased level of H3 K9 dimethylation and decreased levels of H3 K4 trimethylation and H3 K9 acetylation. Reactivation of Ta EXPA1- A and Ta EXPA1- D expression in leaves was correlated with increased levels of H3 K4 trimethylation and H3 K9 acetylation, and decreased levels of H3 K9 dimethylation in their promoters, respectively. Moreover, a higher level of cytosine methylation was detected in the promoter region of Ta EXPA1- B, which may contribute to its silencing in leaves., We demonstrated that epigenetic modifications contribute to the expression divergence of three Ta EXPA1 homoeologs during wheat development. [ABSTRACT FROM AUTHOR]