Evolution of CG Methylation Maintenance Machinery in Plants.

Louis Tirot,Mathieu Ingouff,Pauline E Jullien

doi:10.3390/epigenomes5030019

Abstract

Cytosine methylation is an epigenetic mark present in most eukaryotic genomes that contributes to the regulation of gene expression and the maintenance of genome stability. DNA methylation mostly occurs at CG sequences, where it is initially deposited by de novo DNA methyltransferases and propagated by maintenance DNA methyltransferases (DNMT) during DNA replication. In this review, we first summarize the mechanisms maintaining CG methylation in mammals that involve the DNA Methyltransferase 1 (DNMT1) enzyme and its cofactor, UHRF1 (Ubiquitin-like with PHD and RING Finger domain 1). We then discuss the evolutionary conservation and diversification of these two core factors in the plant kingdom and speculate on potential functions of novel homologues typically observed in land plants but not in mammals.

Highlights

DNA methylation is a highly conserved DNA modification, present across eukaryotes of the plant and animal kingdoms [1,2,3,4]
DNA methylation occurs in CG and non-CG sites (CH, where H = A, T or C) in both mammals and plants, these two types of DNA methylation vary in terms of their genomic distribution and occurrence during development [3,9,10] as well as their dedicated enzymatic machinery [2]
We evaluate the diversification of the central actors in this process during plant evolution

Summary

Introduction

DNA methylation is a highly conserved DNA modification, present across eukaryotes of the plant and animal kingdoms [1,2,3,4]. The Tudor domain of UHRF1 binds H3K9me histone mark (4) and a methylated histone-like motif in DNA ligase 1 (K-LIG1) (5) enzyme that joins Okazaki fragments generated in the lagging strands These interactions further facilitate the maintenance of CG methylation. The different domains of UHRF1 are essential to recruit and activate DNMT1 at hemi-methylated CG DNA ensuring the proper maintenance of DNA methylation during DNA replication In both plant and animal genomes, the presence of DNMT1/UHRF1 homologues coincides with the detection of CG methylation [5,56]. Drosophila and C. elegans genomes typically lack both cytosine methylation and UHRF1 genes [3] These observations suggest a conservation of core mechanisms involved in the maintenance of DNA methylation during evolution. Further experiments are needed to determine if these proteins are still targeted by VIM in plants

Duplication of the MET and VIM Proteins in Plants

Conclusions and Perspectives