Abstract Rapid carotenoid accumulation during postharvest ripening determinants the visual appeal and nutritional quality of mango fruit. Abscisic acid (ABA) is a core phytohormone drives fleshy fruit ripening, yet the regulatory mechanism underlying ABA-enhanced carotenoid biosynthesis in postharvest mango ripening remains largely unclear. Our previous work identified MiPSY1 (phytoene synthase 1), a key structural gene for carotenoid biosynthesis, is transcriptionally activated by the bZIP transcription factor MibZIP66. Here, we show that endogenous ABA level is tightly correlated with carotenoid content during postharvest mango ripening. Exogenous ABA treatment markedly accelerates total carotenoids biosynthesis and upregulates the transcript abundance of both MiPSY1 and MibZIP66. Transient overexpression of MiPSY1 or MibZIP66 in mango fruit, and stable overexpression in transgenic tomato plants, both significantly boosts total carotenoid content. Yeast two-hybrid screening identified MiGF14k, a 14–3-3 family protein, interacting with MibZIP66 in the nucleus, and positively promotes carotenoid biosynthesis. MiGF14k and MibZIP66 synergistically regulated the transcription of MiPSY1 and this synergistic effect was further enhanced by ABA treatment. Furthermore, a phosphorylation-deficient mutation of conserved serine 316 in MibZIP66 eliminates the ABA-enhanced interaction between MibZIP66 and MiGF14k, and impairs the transactivation activity of the complex toward MiPSY1. Our findings uncover a MiGF14k–MibZIP66–MiPSY1 regulatory module that mediates ABA-enhanced carotenoid biosynthesis, in which phosphorylation of MibZIP66 serves as a molecular switch. This work elucidates a positive feedback regulation loop between the ABA signal and carotenoid biosynthesis during mango postharvest ripening, and supplies a molecular basis for breeding high-quality mango.
Wang et al. (Thu,) studied this question.