PbrIDD2-PbrAPX14 Module Functions in the Ethylene-Mediated Ripening and Senescence Process of Pear Fruit

Endogenous H₂O₂ participated in the ethylene-dependent ripening and senescence process of horticultural fruit as a secondary messenger; however, the molecular mechanism beneath such a phenomenon has not been fully clarified until recently. By a conjoint analysis of metabolite, enzyme activities, gene expression profiles in AsA-GSH cycle of 'Kolar' pear, PbrAPX14 might act as a negative factor in the ethylene-mediated H₂O₂ accumulation. PbrAPX14, located in cytosol, would reduce H₂O₂ in vitro and in vivo, inhibit ethylene production, and thus fruit ripening and senescence. After analysing the expression profiles of the differentially expressed transcription factors (TFs) followed by experimental validation, the nuclear PbrIDD2 could directly bind to the cis-acting element (core motif: TTTGTCG) in PbrAPX14 promoter, activate its expression and thus enhance the H₂O₂-scavenging capacity of fruit/calli, which was associated with the mitigated ethylene evolution and fruit ripening and senescence. Further study explored that the H₂O₂-mediated post-translational S-sulfenylation of Cys⁴⁸ residue in PbrAPX14, which mitigated its function, existed in vitro and in vivo, and was upregulated by ethylene, facilitating endogenous H₂O₂ accumulation. Overall, our results implied that both transcriptional and post-translational regulation of PbrAPX14, which were (in)directly under the control of ethylene, functioned in pear ripening and senescence process via regulating endogenous H₂O₂ level.