InterPro domain: IPR044811

DNA glycosylases are required to regulate the DNA methylation pathway at discrete regions across the plant genome, and probably protect the genome from excess methylation [ 1 ]. Arabidopsis encodes four active demethylases with 5-methylcytosine DNA glycosylase/lyase activities, namely DEMETER (DME), DME-Like 1 (DML1)/ROS1 (Repressor of Silencing 1), DML2 and DML3 [ 2 , 3 , 4 , 5 ]. Both ROS1 and DME actively remove DNA methylation in all methylated cytosine contexts through a base excision repair (BER) mechanism [ 6 , 7 ]. DML2/3 and ROS1 play important roles in the regulation of nucleotide-binding leucine-rich repeat (NLR) genes, a class of important plant disease resistance genes [ 8 ].

DEMETER functions mainly in the central cells of female gametophytes involved in gene imprinting, which allows the expression of the maternal copy of the imprinted MEA gene before fertilization, possibly by antagonizing or suppressing DNA methylation on target promoter [ 8 ] and acts in a sequence nonspecific manner. The other three demethylases, ROS1, DML2, and DML3, were shown to be largely active in somatic cells [ 8 ]. ROS1 is constitutively expressed and regulates gene expression by preventing the spread of DNA methylation and transcriptional silencing from transposons and is involved in UV-B induced- and oxidative DNA damage repair [ 8 ]. It also regulates defence genes by demethylation of RMG1 (disease resistance gene) and RLP43 (an orphan immune receptor gene) promoters [ 9 ].

1. DDM1 and ROS1 have a role in UV-B induced- and oxidative DNA damage in A. thaliana. Front Plant Sci 4, 420
2. DEMETER and REPRESSOR OF SILENCING 1 encode 5-methylcytosine DNA glycosylases. Proc. Natl. Acad. Sci. U.S.A. 103, 6853-8
3. The carboxy-terminal domain of ROS1 is essential for 5-methylcytosine DNA glycosylase activity. J Mol Biol 426, 3703-3712
4. AP endonucleases process 5-methylcytosine excision intermediates during active DNA demethylation in Arabidopsis. Nucleic Acids Res 42, 11408-18
5. Impact of DNA Demethylases on the DNA Methylation and Transcription of Arabidopsis NLR Genes. Front Genet 11, 460
6. ROS1, a repressor of transcriptional gene silencing in Arabidopsis, encodes a DNA glycosylase/lyase. Cell 111
7. Dynamics and function of DNA methylation in plants. Nat Rev Mol Cell Biol 19, 803-14
8. Mutations in the DNA demethylase OsROS1 result in a thickened aleurone and improved nutritional value in rice grains. Proc Natl Acad Sci U S A 115, 11327-11332
9. The Arabidopsis active demethylase ROS1 cis-regulates defence genes by erasing DNA methylation at promoter-regulatory regions. Elife 10, 489-506