Redox modification of m⁶A demethylase SlALKBH2 in tomato regulates fruit ripening

Hydrogen peroxide (H₂O₂) functions as a critical signalling molecule in controlling multiple biological processes. How H₂O₂ signalling integrates with other regulatory pathways such as epigenetic modification to coordinately regulate plant development remains elusive. Here we report that SlALKBH2, an m⁶A demethylase required for normal ripening of tomato fruit, is sensitive to oxidative modification by H₂O₂, 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 m⁶A levels and fruit ripening. Our study establishes a molecular link between H₂O₂ and m⁶A methylation and highlights the importance of redox regulation of m⁶A modifiers in controlling fruit ripening.