NAC family gene CmNAC34 positively regulates fruit ripening through interaction with CmNAC-NOR in Cucumis melo

Melon (Cucumis melo) is an economically important horticultural crop cultivated worldwide. NAC (NAM/ATAC/CUC) transcription factors play crucial roles in the transcriptional regulation of various developmental stages in plant growth and fruit development, but their gene functions in melon remain largely unknown. Here, we identified 78 CmNAC family genes with an integrated and conserved no apical meristem (NAM) domain in the melon genome by performing genome-wide identification and bioinformatics analysis. Transcriptome data analysis and qRT-PCR results showed that most CmNACs are specifically enriched in either the vegetative or reproductive organs of melon. Through genetic transformation, we found that overexpression of CmNAC34 in melons led to early ripening fruits, suggesting its positive role in promoting fruit maturation. Using yeast two-hybrid and bimolecular fluorescence complementation assays, we verified the direct protein interaction between CmNAC34 and CmNAC-NOR. The expression patterns of CmNAC34 and CmNAC-NOR were similar in melon tissues, and subcellular localization revealed their nuclear protein characteristics. We transformed CmNAC-NOR in melon and found that its overexpression resulted in early ripening fruits. Then, the yeast one-hybrid and dual luciferase reporter gene assays showed that the CmNAC34 protein can bind to the promoters of two glyoxalase (GLY) genes, which are involved in the abscisic acid signal pathway and associated with fruit regulation. These findings revealed the molecular characteristics, expression profiles, and functional patterns of the NAC family genes and provide new insights into the molecular mechanism by which CmNAC34 regulates climacteric fruit ripening.