DNA methylation mutants in Physcomitrella patens elucidate individual roles of CG and non-CG methylation in genome regulation

• DOI: 10.1073/pnas.2011361117
• Publication Date: 2020-12-23T16:55:09Z
• Authors: Katherine Domb; Aviva Katz; Keith D. Harris; Rafael Yaari; Efrat Kaisler; Vu H. Nguyen; Uyen V. T. Hong; Ofir Griess; Karina G. Heskiau; Nir Ohad; Assaf Zemach
• Keywords: 0301 basic medicine; Epigenome; 03 medical and health sciences; Models, Genetic; Gene Expression Regulation, Plant; Mutation; DNA Transposable Elements; Gene Silencing; DNA Methylation; Bryopsida; Genome, Plant; Up-Regulation; 3. Good health

Significance

While DNA methylation in plants occurs at CG, CHG, and CHH sequence contexts, their comparative roles in genome regulation remain elusive. Here, we utilized Physcomitrella patens as a plant model suitable to study this question. By profiling transcriptomes in a series of context-specific methylation mutants, we found redundancy between asymmetric (CHH) methylation and symmetric methylation in silencing transposons, and that CHH methylation regulates the expression of CG/CHG-depleted transposons. Specific elimination of CG methylation had a significantly smaller effect on transcription than elimination of non-CG methylation. Additionally, we found CHG methylation as a stronger silencer than CG methylation. These results disentangle the transcriptional roles of the individual methylation contexts and elucidate the crucial role of non-CG methylation in genome regulation.