Identification of a Novel Melon Transcription Factor CmNAC60 as a Potential Regulator of Leaf Senescence

NAC transcription factors (TFs) play important roles in plants' responses to abiotic stresses and developmental processes, including leaf senescence. Oriental melon (Cucumis melo var. makuwa Makino) is an important vegetable crop in China and eastern Asia countries. However, little is known about the functions of the melon NAC family members. In this study, a phylogenetic tree was constructed to show that CmNAC60 and the senescence regulator AtNAP were in the same cluster, which implied that CmNAC60 might be a NAC related to leaf senescence. The expression analysis of CmNAC60 in different melon organs showed that the expression of CmNAC60 was highest in the male flowers and lowest in the hypocotyl. In addition, the expression level of CmNAC60 in the senescing leaves was significantly higher than in the non-senescing leaves. Similarly, the expression level of CmNAC60 in the dark-treated leaves was significantly higher than in the untreated leaves. Furthermore, the subcellular localization and transcriptional activation assays indicated that CmNAC60 was a nucleus localized NAC transcription factor with a C-terminal transactivation domain. An analysis of the tissue specific expression showed that the promoter of CmNAC60 may contain cis-acting regulatory elements responsive to leaf senescence. CmNAC60 overexpressing lines of Arabidopsis showed a precocious senescence compared with the wild type (WT). Collectively, our results showed that CmNAC60 was associated with leaf senescence, and could be potentially utilized in molecular breeding to improve melon yield or to extend the postharvest shelf life by delaying leaf senescence.