Active DNA demethylation is an important part of epigenetic regulation in plants and animals. How active DNA demethylation is regulated and its relationship with histone modification patterns are unclear. Here, we report the discovery of IDM1, a regulator of DNA demethylation in Arabidopsis. IDM1 is required for preventing DNA hypermethylation of highly homologous multicopy genes and other repetitive sequences that are normally targeted for active DNA demethylation by Repressor of Silencing 1 and related 5-methylcytosine DNA glycosylases. IDM1 binds methylated DNA at chromatin sites lacking histone H3K4 di- or trimethylation and acetylates H3 to create a chromatin environment permissible for 5-methylcytosine DNA glycosylases to function. Our study reveals how some genes are indicated by multiple epigenetic marks for active DNA demethylation and protection from silencing.

Backgroundm6A is a ubiquitous RNA modification in eukaryotes. Transcriptome-wide m6A patterns in Arabidopsis have been assayed recently. However, differential m6A patterns between organs have not been well characterized.ResultsOver two-third of the transcripts in Arabidopsis are modified by m6A. In contrast to a recent observation of m6A enrichment in 5′ mRNA, we find that m6A is distributed predominantly near stop codons. Interestingly, 85 % of the modified transcripts show high m6A methylation extent compared to their transcript level. The 290 highly methylated transcripts are mainly associated with transporters, stress responses, redox, regulation factors, and some non-coding RNAs. On average, the proportion of transcripts showing differential methylation between two plant organs is higher than that showing differential transcript levels. The transcripts with extensively higher m6A methylation in an organ are associated with the unique biological processes of this organ, suggesting that m6A may be another important contributor to organ differentiation in Arabidopsis. Highly expressed genes are relatively less methylated and vice versa, and different RNAs have distinct m6A patterns, which hint at mRNA fate. Intriguingly, most of the transposable element transcripts maintained a fragmented form with a relatively low transcript level and high m6A methylation in the cells.ConclusionsThis is the first study to comprehensively analyze m6A patterns in a variety of RNAs, the relationship between transcript level and m6A methylation extent, and differential m6A patterns across organs in Arabidopsis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0839-2) contains supplementary material, which is available to authorized users.

The phytohormone abscisic acid (ABA) regulates plant growth, development, and abiotic stress responses. ABA signaling is mediated by a group of receptors known as the PYR1/PYL/RCAR family, which includes the pyrabactin resistance 1–like protein PYL8. Under stress conditions, ABA signaling activates SnRK2 protein kinases to inhibit lateral root growth after emergence from the primary root. However, even in the case of persistent stress, lateral root growth eventually recovers from inhibition. We showed that PYL8 is required for the recovery of lateral root growth, following inhibition by ABA. PYL8 directly interacted with the transcription factors MYB77, MYB44, and MYB73. The interaction of PYL8 and MYB77 increased the binding of MYB77 to its target MBSI motif in the promoters of multiple auxin-responsive genes. Compared to wild-type seedlings, the lateral root growth of pyl8 mutant seedlings and myb77 mutant seedlings was more sensitive to inhibition by ABA. The recovery of lateral root growth was delayed in pyl8 mutant seedlings in the presence of ABA, and the defect was rescued by exposing pyl8 mutant seedlings to the auxin IAA (3-indoleacetic acid). Thus, PYL8 promotes lateral root growth independently of the core ABA-SnRK2 signaling pathway by enhancing the activities of MYB77 and its paralogs, MYB44 and MYB73, to augment auxin signaling.