NAC transcription factor PpNAP4 positively regulates the synthesis of carotenoid and abscisic acid (ABA) during peach ripening.

Yellow-fleshed peaches (Prunus persica (L.) Batsch) are recognized as an excellent dietary source of carotenoids. The metabolic process of carotenoids in plants has been extensively characterized; however, the molecular mechanisms controlling carotenoid accumulation in peaches, particularly the transcriptional regulators upstream this process, remain poorly understood. Here, we initially determined the expression profiles of carotenogenic genes, observing a predominant up-regulation during ripening phase in both yellow- and white-fleshed peaches. This finding, in conjunction with prior research, suggested a conserved biosynthetic pathway for carotenoid synthesis during peach ripening, irrespective of flesh colour. NAC transcription factor, PpNAP4, previously established as a central regulator in peach ripening, is implicated as a potential modulator of carotenoid synthesis. Overexpression assays in peach and tomato nor mutant demonstrated a significant up-regulation of multiple carotenoid components by PpNAP4. Subsequent biochemical experiments revealed that PpNAP4 directly targeted the promoters of carotenogenic genes, thereby activating their expression. Next, PpNAP4 was found to be involved in the synthesis of abscisic acid (ABA) through transcriptional activation of PpNCED2/3. Additionally, we discovered that PpNAP4 acts synergistically with PpNAP6 to jointly regulate carotenoid accumulation and ABA biosynthesis. Collectively, our findings highlight PpNAP4's regulatory function in carotenoids and ABA synthesis during peach fruit ripening.