Ethylene induced CpNAC4 participates in ethylene synthesis by regulating CpACS2 and CpACO4 during papaya fruit ripening

Ethylene plays vital functions in the ripening of papaya, and its biosynthesis mediated by massive TFs which have been researched in various fruits. But the researches on TFs, especially NACs, regulating genes related to ethylene synthesis of papaya is rare. In this study, a new NAC TF, named CpNAC4 belonging to ATAF subfamily, was isolated and identified from papaya. qRT-PCR results showed that CpNAC4, CpACS2 and CpACO4 genes were ripening- and ethylene-induced. Particularly, the promoter activity of CpNAC4 was activated by ethylene, implicating its role in ethylene biosynthesis during fruit ripening. Moreover, CpNAC4 was a transcriptional activator and could bind to and activate CpACS2 and CpACO4 promoters. Taken together, our results revealed that the ethylene-induced CpNAC4 was a transcriptional activator, and might take part in papaya ripening through activation of ethylene biosynthesis related genes to mediate ethylene production, offering new insight of the ethylene biosynthesis regulatory network in fruit ripening. [Display omitted] •CpNAC4, CpACS2 and CpACO4 genes were ripening- and ethylene-induced.•The promoter activity of CpNAC4 was activated by ethylene.•CpNAC4 could bind to and activate CpACS2 and CpACO4 promoters.