Methionine oxidation and reduction of the ethylene signaling component MaEIL9 are involved in banana fruit ripening

The ethylene insensitive 3/ethylene insensitive3-like(EIN3/EIL) plays an indispensable role in fruit ripening. However, the regulatory mechanism that links post-translational modification of EIN3/EIL to fruit ripening is largely unknown. Here, we studied the expression of 13 MaE IL genes during banana fruit ripening, among which MaE IL9 displayed higher enhancement particularly in the ripening stage. Consistent with its transcript pattern, abundance of MaE IL9 protein gradually increased during the ripening process, with maximal enhancement in the ripening. DNA affinity purification(DAP)-seq analysis revealed that MaE IL9 directly targets a subset of genes related to fruit ripening, such as the starch hydrolytic genes MaA MY3D and MaB AM1.Stably overexpressing MaE IL9 in tomato fruit hastened fruit ripening, whereas transiently silencing this gene in banana fruit retarded the ripening process,supporting a positive role of MaEIL9 in fruit ripening. Moreover, oxidation of methionines(Met-129, Met-130, and Met-282) in MaEIL9 resulted in the loss of its DNA-binding capacity and transcriptional activation activity. Importantly, we identified MaEIL9 as a potential substrate protein of methionine sulfoxide reductase A MaMsrA4,and oxidation of Met-129, Met-130, and Met-282in MaEIL9 could be restored by MaMsrA4. Collectively, our findings reveal a novel regulatory network controlling banana fruit ripening, which involves MaMsrA4-mediated redox regulation of the ethylene signaling component MaEIL9.