Transcription Factor CmNAC34 Regulated -Mediated β-Carotene Accumulation during Oriental Melon Fruit Ripening.

Ripened oriental melon () with orange-colored flesh is rich in β-carotene. Lycopene β-cyclase (LCYB) is the synthetic enzyme that directly controls the massive accumulation of β-carotene. However, the regulatory mechanism underlying the -mediated β-carotene accumulation in oriental melon is fairly unknown. Here, we screened and identified a transcription factor, CmNAC34, by combining bioinformatics analysis and yeast one-hybrid screen with promoter. CmNAC34 was located in the nucleus and acted as a transcriptional activator. The expression profile of was consistent with that of during the fruit ripening. Additionally, the transient overexpression of CmNAC34 in oriental melon fruit promoted the expression of and enhanced β-carotene concentration, while transient silence of CmNAC34 in fruit was an opposite trend, which indicated CmNAC34 could modulate -mediated β-carotene biosynthesis in oriental melon. Finally, the yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), β-glucuronidase (GUS) analysis assay, and luciferase reporter (LUC) assay indicated that CmNAC34 could bind to the promoter of and positively regulated the transcription level. These findings suggested that CmNAC34 acted as an activator to regulate β-carotene accumulation by directly binding the promoter of , which provides new insight into the regulatory mechanism of carotenoid metabolism during the development and ripening of oriental melon.