CstMYB1R1, a REVEILLE-8-like transcription factor, regulates diurnal clock-specific anthocyanin biosynthesis and response to abiotic stress in Crocus sativus L.

ABSTRACT

KEY MESSAGE CstMYB1R1 acts as a positive regulator of Crocus anthocyanin biosynthesis and abiotic stress tolerance which was experimentally demonstrated through molecular analysis and over-expression studies in Crocus and Nicotiana. Regulatory mechanics of flavonoid/anthocyanin biosynthesis in Crocus floral tissues along the diurnal clock has not been studied to date. MYB proteins represent the most dominant, functionally diverse and versatile type of plant transcription factors which regulate key metabolic and physiological processes in planta. Transcriptome analysis revealed that MYB family is the most dominant transcription factor family in C. sativus. Considering this, a MYB-related REVEILLE-8 type transcription factor, CstMYB1R1, was explored for its possible role in regulating Crocus flavonoid and anthocyanin biosynthetic pathway. CstMYB1R1 was highly expressed in Crocus floral tissues, particularly tepals and its expression was shown to peak at dawn and dusk time points. Anthocyanin accumulation also peaked at dawn and dusk and was minimum at night. Moreover, the diurnal expression pattern of CstMYB1R1 was shown to highly correlate with Crocus ANS/LDOX gene expression among the late anthocyanin pathway genes. CstMYB1R1 was shown to be nuclear localized and transcriptionally active. CstMYB1R1 over-expression in Crocus tepals enhanced anthocyanin levels and upregulated transcripts of Crocus flavonoid and anthocyanin biosynthetic pathway genes. Yeast one hybrid (Y1H) and GUS reporter assay confirmed that CstMYB1R1 interacts with the promoter of Crocus LDOX gene to directly regulate its transcription. In addition, the expression of CstMYB1R1 in Nicotiana plants significantly enhanced flavonoid and anthocyanin levels and improved their abiotic stress tolerance. The present study, thus, confirmed positive role of CstMYB1R1 in regulating Crocus anthocyanin biosynthetic pathway in a diurnal clock-specific fashion together with its involvement in the regulation of abiotic stress response.