MaUGT79 confers drought tolerance by regulating scopolin biosynthesis in plants

The coumarin scopoletin and its glycosylated form scopolin constitute a vast class of natural products that are considered to be high-value compounds, distributed widely in the plant kingdom, they help plants adapt to environmental stresses. However, the underlying molecular mechanism of how scopolin is involved in the regulation of plant drought tolerance remains largely unexplored. Here, UDP-glycosyltransferase 79 (MaUGT79) was genetically mapped as the target gene by bulk segregant analysis sequencing (BSA-seq) from two Melilotus albus near-isogenic lines (NILs). MaUGT79 exhibits glucosyltransferase activity toward scopoletin. The expression of MaUGT79 is induced by drought stress and it was found to mediate scopolin accumulation and reactive oxygen species (ROS) scavenging under drought stress. Moreover, the transcription of MaUGT79 was demonstrated to be directly and positively regulated by MaMYB4, which is a key integrator of both scopolin biosynthesis and drought tolerance. Collectively, this study reveals that MaMYB4 is a positive regulator in drought stress by targeting the MaUGT79 promoter and activating its expression to coordinately mediate scopolin biosynthesis and drought tolerance, providing insights into the regulatory mechanism for plant growth adaption to environmental changes through accumulation of scopolin.