ROS1 promotes low temperature-induced anthocyanin accumulation in apple by demethylating the promoter of anthocyanin-associated genes

Low temperature can affect the growth and development of plants through changes in DNA demethylation patterns. Another known effect of low temperature is the accumulation of anthocyanin pigments. However, it is not known whether the two phenomena are linked, specifically whether DNA demethylation participates in anthocyanin accumulation in response to low-temperature stress. The ROS1 gene is involved in plant DNA demethylation and influences methylation levels in response to low-temperature stress. In this study, using RNA sequencing, we detected the transcription levels of MdROS1, as well as those of anthocyanin biosynthesis-related genes, correlate with the anthocyanin content in apple (Malus domestica), at low temperature. Genomic bisulfite sequencing showed that the methylation levels of the promoters of the anthocyanin-related genes MdCHS, MdCHI, MdF3′H, MdANS, MdUFGT, and MdMYB10 decreased in apple leaves after low-temperature treatment. Similar expression and methylation results were found in apple fruit. Transiently silencing MdROS1 in the leaves and fruit of apple cultivars inhibited the accumulation of anthocyanins and led to decreased expression of anthocyanin biosynthetic genes, and the opposite results were detected in MdROS1-overexpressing leaves and fruit. A promoter binding assay showed that the conserved RRD-DME domains of MdROS1 bind directly to the promoters of MdF3′H and MdUFGT. Taken together, these results suggest that ROS1 affects the anthocyanin biosynthetic pathway by decreasing the methylation level of anthocyanin-related gene promoters, thereby increasing their expression and increasing anthocyanin accumulation.