Methionine oxidation-regulated MaERF95L controls starch and sucrose metabolism in postharvest banana during ripening

Abstract

The conversion of starch into sugar during postharvest banana (Musa acuminata, AAA group) ripening significantly influences fruit quality. Ethylene response factors (ERFs) regulate fruit ripening through ethylene signaling, while redox modifications affect their activity by post-translational changes. This study identifies MaERF95L, an EDLL-domain ERF in banana, as a central regulator of starch-to-sugar metabolism during postharvest ripening. Using electrophoretic mobility shift and dual-luciferase reporter assays, we demonstrate that MaERF95L directly binds to and activates the expression of six genes related to starch degradation and sucrose synthesis (MaGWD1, MaAMY3, MaBAM1, MaHK5, MaPGI1, and MaUPG3). MaERF95L overexpression accelerates starch degradation and sugar accumulation in both banana and tomato fruits during ripening. Notably, methionine (Met, M)-based oxidation modifications (e.g., Met-16 and Met-77) suppress MaERF95L's transcriptional regulatory function. Simulating oxidation by Met→glutamine (Gln, Q) substitutions (MaERF95L^M16Q/M77Q) alters its subcellular localization and also impairs its DNA-binding and transcriptional activation capabilities. In contrast, blocking oxidation by Met→Valine (Val, V) substitutions (MaERF95L^M16V/M77V) maintains its transcriptional activation activity. Furthermore, transient overexpression of MaERF95L^M16Q/M77Q in bananas reduced MaERF95L's activation of genes related to starch degradation and sucrose synthesis, and starch-to-sugar conversion. However, the overexpression of MaERF95L^M16V/M77V showed no effect on MaERF95L's activation function. These findings reveal a Met oxidation-sensitive regulatory mechanism connecting reactive oxygen species signaling to carbohydrate metabolism, providing molecular insights into quality formation regulation during ripening and potential strategies for reducing postharvest losses in climacteric fruits.