Redox modification of mA demethylase SlALKBH2 in tomato regulates fruit ripening.

Hydrogen peroxide (HO) functions as a critical signalling molecule in controlling multiple biological processes. How HO signalling integrates with other regulatory pathways such as epigenetic modification to coordinately regulate plant development remains elusive. Here we report that SlALKBH2, an mA demethylase required for normal ripening of tomato fruit, is sensitive to oxidative modification by HO, which leads to the formation of homodimers mediated by intermolecular disulfide bonds, and Cys39 serves as a key site in this process. The oxidation of SlALKBH2 promotes protein stability and facilitates its function towards the target transcripts including the pivotal ripening gene SlDML2 encoding a DNA demethylase. Furthermore, we demonstrate that the thioredoxin reductase SlNTRC interacts with SlALKBH2 and catalyses its reduction, thereby modulating mA levels and fruit ripening. Our study establishes a molecular link between HO and mA methylation and highlights the importance of redox regulation of mA modifiers in controlling fruit ripening.