ADVANCES IN THE FUNCTIONALSTUDY OF THE ARABIDOPSIS DNAGLYCOSYLASE MBD4L

Torres JR, Lescano I, ÁlvarezME

Centro deinvestigaciones en Química Biológica de Córdoba (CIQUIBIC, CONICET-UNC),Departamento de Química Biológica, Facultad de Ciencias Químicas, UniversidadNacional de Córdoba.

DNA glycosylases play important roles in the life of allorganisms, acting at initial stages of the base excision DNA repair system thatexcises and replaces damaged bases from DNA. Interestingly, some particular DNAglycosylases remove 5-methylcytosine (5-mC), whose replacement by cytosine (C)can produce DNA demethylation. In Arabidopsis, DNA glycosylases from the DEMETERfamily have such capacity, and act over some well characterized targets. Here,we studied a novel DNA glycosylase recently described named MBD4L(methyl-binding domain protein 4 like), that is homologous to the human DNAglycosylase MBD4. Curiously, MBD4L does not recognize 5-mC in vitro. Even so, we evaluated if MBD4L can affect DNA methylationof some particular genomic regions. For that, we selected genomic targets withdifferent chromatin states (euchromatic- heterochromatic) and used CHOP-PCRassays to determine their methylation level. Studies were conducted in wild-type,mbd4l mutant and MBD4L over-expressingplants, under both basal and stress conditions. We found that MBD4L controls DNAmethylation at loci having different chromatin states. Moreover, the enzyme affectsDNA methylation both at basal and stress condition. These results suggest that theaction of MBD4L is not restricted to a particular chromatin state and probably contributesto stress-induced responses. The putative effects of MBD4L on the differentgenomic sites and on transcriptional regulation will be discussed.

Keywords:epigenetics, DNA demethylation, chromatin state, gene expression, DNAglycosylases, stress.