Critical roles of DNA demethylation in the activation of ripening-induced genes and inhibition of ripening-repressed genes in tomato fruit

Significance DNA methylation is generally considered an epigenetic mark for transcriptional gene silencing. In this work, we generated loss-of-function mutant alleles of SlDML2 . We characterized the mutant fruits that failed to ripen and discovered that SlDML2 is required for the demethylation and activation of genes important for fruit ripening, including genes involved in fruit pigment and flavor synthesis, ethylene synthesis and signaling, and cell wall hydrolysis. Unexpectedly, we found that SlDML2-mediated DNA demethylation is also necessary for fruit ripening-induced repression of hundreds of genes involved in photosynthesis and cell wall synthesis and organization. Our study has therefore revealed a broad and critical role of DNA methylation as an activation mark for the expression of many genes in a eukaryotic organism.