plays a role in DNA demethylation and disease response in somatic tissues of Arabidopsis.

DNA demethylases function in conjunction with DNA methyltransferases to modulate genomic DNA methylation levels in plants. The Arabidopsis genome contains four DNA demethylase genes, ( () also known as ( and . While and were shown to function in disease response in somatic tissues, has been thought to function only in reproductive tissues to maintain the maternal-specific expression pattern of a subset of imprinted genes. Here we used promoter:β-glucuronidase (GUS) fusion constructs to show that is constitutively expressed throughout the plant, and that and have tissue-specific expression patterns. Loss-of-function mutations in cause seed abortion and therefore viable mutants are not available for gene function analysis. We knocked down expression in a triple () mutant background using green tissue-specific expression of a hairpin RNA transgene (RNAi), generating a viable 'quadruple' demethylase mutant line. We show that this RNAi line has enhanced disease susceptibility to infection compared to the triple mutant. Furthermore, several defence-related genes, previously shown to be repressed in , were further repressed in the RNAi plants. DNA methylation analysis of two of these genes revealed increased differential promoter DNA methylation in RNAi plants compared to WT, beyond the difference observed in the parental plants. These results indicate that contributes to DNA demethylase activity and disease response in somatic tissues.