H2O2 oxidation of VvMYB APL reduces VvHSP20-43 expression and promotes grape ripening.

Previous studies have shown that hydrogen peroxide (H2O2) treatment promotes early ripening in "Kyoho" grapes (Vitis vinifera × Vitis labrusca); however, the mechanism by which H2O2 oxidation modification regulates grape ripening remains unclear. Here, RNA-Seq data revealed substantial downregulation of small Heat Shock Protein 20-43 (VvHSP20-43) expression levels in the treated group. Co-expression network analysis identified MYB Altered Phloem Development (VvMYB APL) as a key regulator of VvHSP20-43 expression. Dual luciferase, yeast one-hybrid, and electrophoretic mobility shift assays confirmed that VvMYB APL binds to the VvHSP20-43 promoter, thereby activating its transcriptional expression. Stable transformation in Arabidopsis and transient transformation in grape berries demonstrated that VvMYB APL and VvHSP20-43 negatively regulate fruit ripening. Further analysis revealed that exogenous H2O2 treatment rapidly oxidizes the VvMYB APL protein, inducing methionine (Met) site mutations that inhibit its transcriptional activation of VvHSP20-43. In addition, reduced expression of VvMYB APL and VvHSP20-43 promoted the expression of ripening-related genes, thereby accelerating grape berry ripening. This study elucidates the molecular mechanism by which H2O2 oxidizes the VvMYB APL transcription factor, thereby downregulating VvHSP20-43 expression and influencing fruit ripening.