Maintenance of CpG methylation is essential for epigenetic inheritance during plant gametogenesis

Abstract

In mammals, the DNA methyltransferase 1 (Dnmt1) faithfully copies the pattern of cytosine methylation at CpG sites to the newly synthesized strand, and this is essential for epigenetic inheritance. In Arabidopsis thaliana, several DNA methyltransferases or chromatin modifiers coupled to methylation changes have been characterized, and mutations that cause loss of their function are recessive. This is surprising because plant gametogenesis includes postmeiotic DNA replication in haploid nuclei before fertilization. Therefore, the recessive character of the mutations excludes the affected components from a regulatory role in postmeiotic maintenance or modification of epigenetic states. Here we show, however, that depletion of A. thaliana MET1, a homolog of mammalian Dnmt1 (ref. 8), results in immense epigenetic diversification of gametes. This diversity seems to be a consequence of passive postmeiotic demethylation, leading to gametes with fully demethylated and hemidemethylated DNA, followed by remethylation of hemimethylated templates once MET1 is again supplied in a zygote.

Methylome analysis reveals an important role for epigenetic changes in the regulation of the Arabidopsis response to phosphate starvation

“…1B). For example, the expression of MET1, which is mainly involved in the maintenance of CG DNA methylation (27,28), was twofold greater under LP compared with HP conditions. Similar results were observed for DRM1 and DRM2.…”

Finding the fifth base: Genome-wide sequencing of cytosine methylation

“…DNA methylation is established by the de novo DNA methyltransferases DNMT3A and DNMT3B in mammals (Okano et al 1999) and the orthologous DOMAINS REARRANGED METHYLTRANSFERASE 1/2 (DRM1/2) in plants that are targeted to methylate-specific genomic loci by small RNA molecules in the process of RNA-directed DNA methylation Cao et al 2003). Post-replicative maintenance of DNA methylation at CG sites is catalyzed by the DNA methyltransferase DNMT1 in mammals and its ortholog METHYL-TRANSFERASE 1 (MET1) in plants, while the plant-specific DNA methyltransferase CHROMOMETHYLASE 3 is required for maintenance of DNA methylation at CHG sites in plants (Finnegan and Dennis 1993;Bartee et al 2001;Bird 2002;Jackson et al 2002;Kankel et al 2003;Saze et al 2003;Goll and Bestor 2005). Furthermore, plants possess the demethylase enzymes ROS1, DME, DML2, and DML3 that remove methylcytosines by a baseexcision-mediated repair process (Gong et al 2002;Penterman et al 2007), and a recent study indicates that small RNA molecules can target the ROS1 demethylase to specific genomic target regions via the RNA-binding protein AT5G58130 (also known as ROS3) (Zheng et al 2008).…”

Hypomethylated Pollen Bypasses the Interploidy Hybridization Barrier inArabidopsis

“…Arabidopsis thaliana mutants jas-3 (Erilova et al, 2009), fis2-5 (Weinhofer et al, 2010, and met1-3 (Saze et al, 2003) are in the Col-0 accession. The osd1-1 mutant (d'Erfurth et al, 2009) was kindly provided by Raphael Mercier.…”