DEMETHYLATION REGULATOR 1 regulates DNA demethylation of the nuclear and mitochondrial genomes.

Active DNA demethylation effectively modulates gene expression during plant development and in response to stress. However, little is known about the upstream regulatory factors that regulate DNA demethylation. We determined that the demethylation regulator 1 (demr1) mutant exhibits a distinct DNA methylation profile at selected loci queried by methylation-sensitive polymerase chain reaction and globally based on whole-genome bisulfite sequencing. Notably, the transcript levels of the DNA demethylase gene REPRESSOR OF SILENCING 1 (ROS1) were lower in the demr1 mutant. We established that DEMR1 directly binds to the ROS1 promoter in vivo and in vitro, and the methylation level in the DNA methylation monitoring sequence of ROS1 promoter decreased by 60% in the demr1 mutant. About 40% of the hyper-differentially methylated regions (DMRs) in the demr1 mutant were shared with the ros1-4 mutant. Genetic analysis indicated that DEMR1 acts upstream of ROS1 to positively regulate abscisic acid (ABA) signaling during seed germination and seedling establishment stages. Surprisingly, the loss of DEMR1 function also caused a rise in methylation levels of the mitochondrial genome, impaired mitochondrial structure and an early flowering phenotype. Together, our results show that DEMR1 is a novel regulator of DNA demethylation of both the nuclear and mitochondrial genomes in response to ABA and plant development in Arabidopsis.