DNA Methylation Is Regulated by Sumoylation through Action of E3 SUMO ligase AtSIZ1 in Arabidopsis

Abstract

In eukaryotes, gene expression is controlled at multiple levels, and DNA methylation, one of several epigenetic mechanisms, also has large influence on transcription. Sumoylation is an important posttranslational modification regulating various biological processes. We therefore investigated the effect of sumoylation on epigenetic gene expression. To do this, we used siz1-2 mutant, one of T-DNA insertional mutated alleles of AtSIZ1 encoding an Arabidopsis E3 SUMO ligase. DNA methylation was examined by McrBC-PCR using genomic DNAs that were isolated from one-week old or four-week old wild-type and siz1-2 mutant plants. Results showed that the methylation levels of retrotransposon ATGP1, ATCOPIA4, ATLINE1-4, ATSN1 and DNA transposon ATMU1 were much lower in siz1-2 mutant than in wild-type at mature stage while there is no significant difference in their methylation levels between wild-type and siz1-2 mutant plants at seedling stage. Evaluation of the methylcytosine proportion in CG, CHG and CHH sites of ATMU1 by bisulfite sequencing revealed that methylation levels in both CHG and CHH sites were decreased in siz1-2 mutants in comparison with that in wild-type plants, in particular in CHH site. However, methylation in CG site was only slightly low in siz1-2 mutant plants. Interestingly, this phenomenon also only occurs at maturation stage. All of these data demonstrate that AtSIZ1 can regulate DNA or histone methyltransferse activities through its E3 SUMO ligase activity, resulting in modulation of gene expression, which strongly implies that sumoylation is tightly linked with DNA methylation.