Is the cytosine DNA methyltransferase gene MET1 regulated by DNA methylation in Arabidopsis thaliana plants?

The methylation patterns of the MET1 gene in organs of Arabidopsis thaliana were studied by Southern blot hybridization of DNA samples hydrolyzed with differentially methylation-sensitive restriction endonucleases. A highly methylated on internal cytosine residue CCGG site was found 1.5 kb upstream of the gene, whereas CCGG sites located in more proximal parts of the 5'-flanking region and the gene itself are essentially unmethylated. This methylation pattern was observed in different organs of plants belonging to two different ecotypes as well as in different transgenic plant lines. The methylation level of a CCGG site in exon 3 (2.1 kb from the gene's 5'-end) occurred to be variable between different transgenic plant lines and two ecotypes studied. Transcription levels of the MET1 gene vary slightly in organs of wild-type plants without any obvious correlation with its methylation. The transgenic antisense MET1 constructs expressed in plant genome do affect both MET1 methylation and its transcription but again without any obvious correlation. The comparative investigation of transcription levels of different genes of cytosine DNA methyltransferase family MET (MET1, MET2a, MET2b, MET3) and their methylation patterns shows that there may exist some mechanisms defending the most actively transcribed gene MET1 of this family from methylation mediated silencing. In contrast to DRM2 gene we could not find any adenine methylated GATC sites in the MET1 gene.