Functional Analysis of the Transcription Factor CcbHLH107 in Regulating the Color Change of Mandarin Fruits

CcbHLH107 was cloned from early ripening mandarin fruits grown in Chongqing, and its biological information and transcription factor characteristics were analyzed. The results showed that CcbHLH107 had high homology with Arabidopsis thaliana AtbHLH107, and its promoter region contained various types of response elements such as light-responsive, abscisic acid-responsive and growth hormone-responsive elements. CcbHLH107 was localized in the nucleus and had transcriptional activation activity. One week after heterologous transient overexpression of CcbHLH107 in tobacco leaves, the leaves were significantly yellowed, and the contents of chlorophyll and its metabolite in the leaves were significantly reduced (P < 0.05). At three days after transient overexpression in early maturing mandarin fruits, obvious color changes in the peel were observed, and the expression level of CcbHLH107 in the peel was significantly increased. Compared with the control group, the contents of chlorophyll and its metabolites in the peel decreased faster in the CcbHLH107 overexpression group, and the contents of different carotenoids changed, among which the accumulation of lutein, cryptoxanthin and zeaxanthin was promoted. In addition, the expression of the chlorophyll degradation-related genes CcNYC1, CcChlase1, CcRCCR, and CcPAO and of the carotenoid regulation-related genes CcPSY2, CcBCH2, CcZEP, CcNCED5, CcCCS, and CcCCD4 was significantly up-regulated (P < 0.05). In conclusion, CcbHLH107 accelerates the yellowing of mandarin fruits by promoting the degradation of chlorophyll and altering the contents of different carotenoids and their ratios.