Drought Stress Response in Arabidopsis DNA Demethylase Mutants

DNA methylation is a primary epigenetic modification that regulates gene expression and transposon silencing. In plants DNA demethylation is achieved by the DNA glycosylases that specifically excise 5-methylcytosine (5mC). DEMETER (DME) is a founding member of 5mC DNA glycosylase family genes in Arabidopsis along with ROS1, DML2 and DML3. The DME family genes are exclusively identified in the plant kingdom from green algae to angiosperms. All members in the family have three conserved domains in common with highly variable regions between them. We previously demonstrated that besides the central glycosylase domain, two additional domains of unknown function are required for 5mC excision. The phylogenetic analysis on the DME family proteins revealed that DME and ROS1 orthology groups are major and most closely related to each other while retaining the DML2 as a small subgroup. The DML3 orthology group is distantly related and contains most members from algae and moss, suggesting that DML3 is the least diverged in the family. In order to assess their functions in response to environmental stress, we performed a germination test with ros1, dml2, and dml3 mutants in Arabidopsis. All ros1, dml2, and dml3 single mutants were hypersensitive to both high salt and ABA, displaying significantly reduced germination rates. Under osmotic stress conditions, both ros1 and dml2 mutants were hypersensitive, whereas the dml3 mutants were relatively normal. This study suggests that DME family genes have evolved with functional divergence and play an important role for stress tolerance possibly by regulating the epigenome structure.