A R3-Type MYB Transcription Factor LrMYB30 Negatively Regulates L. ruthenicum Fruit Coloration

Background: Anthocyanins and proanthocyanidins (PAs), as flavonoid compounds with potent antioxidant activity, exhibit significant health-promoting and medicinal properties. Black wolfberry (Lycium ruthenicum Murr.) is renowned for its exceptional anthocyanin content; however, the regulatory mechanisms of anthocyanin biosynthesis remain poorly understood, limiting its biotechnological potential. This study aimed to elucidate the transcriptional regulatory function of LrMYB30 in anthocyanin biosynthesis in black wolfberry. Methods: The regulatory function of LrMYB30 was investigated using virus-induced gene silencing (VIGS), yeast one-hybrid assays, and dual-luciferase reporter assays in black wolfberry. Results: VIGS demonstrated that silencing LrMYB30 promoted anthocyanin accumulation while reducing PA content, establishing that the LrMYB30 transcription factor as a negative regulator of anthocyanin synthesis. Yeast one-hybrid and dual-luciferase reporter assays confirmed that LrMYB30 directly binds to and activates the promoter of LrANR, a key structural gene in PA biosynthesis. In contrast, LrMYB30 neither binds to nor suppresses the promoters of the critical anthocyanin biosynthesis genes LrUF3GT and LrDFR. Conclusions: Thus, LrMYB30 redirects the flavonoid metabolic flux from anthocyanin to PA synthesis through transcriptional activation of LrANR during later fruit development, reducing anthocyanin accumulation and delaying coloration. These findings reveal a novel regulatory mechanism in black wolfberry pigmentation and maturation, providing genetic targets for molecular breeding of high-anthocyanin cultivars.