Pepper (Capsicum annuum L.) as a non-climacteric fruit is usually harvested at either mature green or ripe stage, and fruit quality including texture, color, and nutritive values is different according to the fruit developmental stages. Understanding molecular mechanisms of fruit ripening and senescence processes is crucial to control the fruit quality and reduce the postharvest loss. This study was aimed to identify NAC transcription factors (TFs) involved in the ripening and senescence of pepper fruit by analyzing gene expressions and protein-protein interactions. To identify NAC genes related to the ripening, transcript levels of total 104 NAC TFs were investigated using publicly available transcriptome data. Among them, transcript levels of 8 genes significantly increased during the ripening and senescence. Their phylogenetic analysis also showed that they are closely associated with NAC TFs which play a role in ripening or senescence in other crop species. Among them, 4 genes showing abundant transcript levels at the ripening stage were selected, including CaNAC14, 45, 84, and 92, to further investigate their roles. In pepper (C. annuum var. ‘Gyeonggiyangpyeiong’) fruit, their expressions clearly increased during the ripening or induced by exogenous ABA, the major phytohormone regulating non-climacteric fruit ripening. To reveal a relationship between the CaNACs and ABA signaling, protein-protein interactions between the CaNACs and ABA receptors were analyzed through yeast- two-hybrid and bimolecular-fluorescence complementation assays. Among them, CaNAC92 and CaPYL12, the ABA receptor, interacted each other in a nucleus with an ABA-dependent manner. This result indicated that their interaction may affect the ABA signaling or the transcriptional regulation during the ripening. We identified CaNAC TFs involved in the pepper fruit ripening and suggested CaNAC92 as a putative molecule functioning in the ripening. These findings will provide genetic information to control the ripening and to improve pepper fruit quality.
