NAC transcription factor PpNAP4 modulates sucrose accumulation by activating the expression of PpSUS1 and PpSPS2 during peach ripening

Sugars are crucial in determining fruit quality and significantly affect the commercial value. Sucrose is the primary soluble sugar in ripe peach fruit. However, the regulatory mechanism of sucrose synthesis in peach fruit, especially during natural ripening, remains largely unexplored. This study identified two structural genes of peach (Prunus persica, ‘Jinlinghuanglu’), PpSUS1 and PpSPS2, whose expression was strongly correlated with sucrose accumulation. The transcription factors that regulated the expression of these two genes during peach fruit ripening were screened; and three NACs (NAM, ATAF1/2 and CUC2), whose expression also significantly correlated with sucrose accumulation, were identified. Notably, PpNAP4 (NAC-like, activated by APETALA3/PISTILLATA) displayed the highest activation activity toward the PpSUS1 and PpSPS2 promoters. The direct binding activity was confirmed using luciferase imaging and electrophoretic mobility shift assays. The sucrose content and expression of sucrose synthesis-related genes significantly increased when PpNAP4 was overexpressed in peach fruit and the tomato nor mutant. Moreover, PpNAP4 functioned synergistically with PpNAP6 to modulate sucrose synthesis, and PpNAP4 targeted its own promoter and feedback-activated its own expression. This research unveils a novel regulatory mechanism controlling sucrose accumulation in peach fruit.