The mechanism of dynamic equilibrium of ascorbate redox status mediated by PbrDHAR5 during scald development in pear fruit

Ascorbate (AsA) redox status participated in the scald development of Pyrus bretschneideri Rehd. fruit as a cellular redox sensor. By a conjoint analysis of metabolites, enzyme activities and gene expression profiles in AsA-GSH cycle of the chilled pear, PbrDHAR5 was characterized as the candidate gene involved in this process. PbrDHAR5, located in cytosol and nucleus, catalyzed DHA reduction into AsA in vitro and in vivo, elevating AsA redox status and thus fruit chilling tolerance; moreover, the catalytic Cys²⁰ residue in PbrDHAR5 played critical role in this reaction. After analyzing the expression profiles of the differentially expressed TFs, PbrWRKY83 demonstrated higher correlation with PbrDHAR5 than others. PbrWRKY83, located in nucleus, could interact with the only two W-box elements in PbrDHAR5 promoter as monomer and then activate its expression, leading to the improvement of AsA redox status and thus fruit chilling tolerance. In a further study, we explored that the H₂O₂-mediated S-sulfenylation of Cys²⁰ residue in PbrDHAR5 accumulated upon scald development, suppressed its activity, and thus caused the decrement of AsA redox status. Taken together, our results implied that the H₂O₂-mediated S-sulfenylation of PbrDHAR5 attenuates the role of PbrWRKY83-PbrDHAR5 module, which positively regulates AsA redox status during scald development in pear.