High-CO2/hypoxia-modulated NAC transcription factors involved in de astringency of persimmon fruit

Most of the cultivated persimmon fruits belong to the astringent type, which require postharvest astringency removal to reach edible quality. High CO2 (mostly > 90%) treatment has been widely used for persimmon fruit deastringency and is controlled by several different transcription factors (DkERFs, DkMYBs and DkTGAs). However, the responses of DkNACs to high CO2 and low oxygen, as well as their regulatory roles in deastringency, are still not fully understood. In the present research, six DkNACs (DkNAC13-18) were isolated from persimmon fruit. Phylogenetic and sequence analyses predicted that DkNAC13/15/18 might be hypoxia-responsive and possibly involved in regulating the persimmon deastringency, according to the functions of their putative homologs. Gene expression analysis indicated that DkNACs 13-18 were all regulated by artificial high-CO2 atmosphere (1% O-2 and 95% CO2, AHCA), with DkNACs 13-17 being up-regulated and DkNAC18 down-regulated. Dual-luciferase assay further indicated that DkNAC13 significantly activated the promoter of DkERF9 (an activator of DkPDC2), meanwhile, DkNAC16 acted as an activator of a deastringency related structural gene (DkADH1). Thus, the present study indicated six high-CO2/hypoxia- modulated DkNAC genes, with at least two novel DkNAC genes (DkNAC13/16) were characterized as putative activators for deastringency, acting on DkERF9 and DkADH1 respectively.