Convergent and divergent regulations of ethylene and abscisic acid biosynthesis during persimmon fruit postharvest ripening

Phytohormones are signaling molecules produced by plants and play pivotal roles in various physiological and developmental processes. Ethylene and abscisic acid (ABA) are usually considered to have separate roles in regulating fruit ripening and co-regulation involving both hormones have rarely been investigated. Here, similar changes in ethylene and ABA were observed underlying postharvest persimmon ripening. High CO2 (95% CO2, 1% O2) and high CO2 + 1-methylcyclopropene (CO2 + 1-MCP) are two widely used commercial deastringency treatments for persimmon, which accumulate acetaldehyde by anaerobic metabolism to precipitate astringent soluble tannins. Unexpectedly, CO2 treatment triggered the accumulation of both ethylene and ABA. This could be inhibited by CO2 + 1-MCP, which also prevented CO2-driven rapid softening. Three differentially expressed genes, DkACS1, DkNCED1 + 3′ and DkNCED2 + 3′ involved in ethylene and ABA synthesis were identified, but none of the differentially expressed transcription factors tested showed any obvious transactivation effects on their gene promoters. RNA binding protein DkRBM24–1 was shown to regulate the transcription of DkACS1 and DkNCED2 + 3′ by binding to the 3′UTR region of their mRNA. Further analysis indicated that DkbHLH11 was able to activate the expression of DkNCED1 + 3′ after phosphorylation by protein kinase DkMAPKKK1. Overall, the present study indicated the ethylene and ABA production in ripening fruit have both shared (DkRBM24–1) and distinct (DkbHLH11) regulators.