Asymmetric epigenome maps of subgenomes reveal imbalanced transcription and distinct evolutionary trends in Brassica napus

• Published in: Molecular plant Vol. 14; no. 4; pp. 604 - 619
• Main Authors: Zhang, Qing, Guan, Pengpeng, Zhao, Lun, Ma, Meng, Xie, Liang, Li, Yue, Zheng, Ruiqin, Ouyang, Weizhi, Wang, Shunyao, Li, Hongmeijuan, Zhang, Ying, Peng, Yong, Cao, Zhilin, Zhang, Wei, Xiao, Qin, Xiao, Yuanling, Fu, Tingdong, Li, Guoliang, Li, Xingwang, Shen, Jinxiong
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 05.04.2021
• Subjects: Brassica napus; ChIP-seq; epigenome; gene expression; Brassica napus; ChIP-seq; epigenome; gene expression
• ISSN: 1674-2052; 1752-9867
• DOI: 10.1016/j.molp.2020.12.020

The complexity of the epigenome landscape and transcriptional regulation is significantly increased during plant polyploidization, which drives genome evolution and contributes to the increased adaptability to diverse environments. However, a comprehensive epigenome map of Brassica napus is still unavailable. In this study, we performed integrative analysis of five histone modifications, RNA polymerase II occupancy, DNA methylation, and transcriptomes in two B. napus lines (2063A and B409), and established global maps of regulatory elements, chromatin states, and their dynamics for the whole genome (including the An and Cn subgenomes) in four tissue types (young leaf, flower bud, silique, and root) of these two lines. Approximately 65.8% of the genome was annotated with different epigenomic signals. Compared with the Cn subgenome, the An subgenome possesses a higher level of active epigenetic marks and lower level of repressive epigenetic marks. Genes from subgenome-unique regions contribute to the major differences between the An and Cn subgenomes. Asymmetric histone modifications between homeologous gene pairs reflect their biased expression patterns. We identified a novel bivalent chromatin state (with H3K4me1 and H3K27me3) in B. napus that is associated with tissue-specific gene expression. Furthermore, we observed that different types of duplicated genes have discrepant patterns of histone modification and DNA methylation levels. Collectively, our findings provide a valuable epigenetic resource for allopolyploid plants. Comprehensive epigenomic maps of Brassica napus are still unavailable. In this study, the authors established comprehensive reference epigenomic maps, annotated over 65.8% of the genome with different epigenome properties, and identified a novel bivalent chromatin state (H3K4me1/H3K27me3), providing the epigenomic basis for the asymmetric expression between the An and Cn subgenomes in Brassica napus.