MsCCoAOMTh3 confers drought tolerance by mediating lignin content and ROS scavenging

Caffeoyl-CoA O-methyltransferase (CCoAOMT) is a key enzyme in the phenylpropanoid pathway that plays a crucial role in lignin biosynthesis; however, its functional role in Medicago sativa remains poorly understood. In this study, we identified 44 MsCCoAOMT family members and analyzed their expression profiles across eight tissues and under polyethylene glycol (PEG)-induced osmotic stress. Among them, MsCCoAOMTh3 displayed preferential expression in roots and flowers, and was significantly upregulated in roots and stems following PEG treatment, suggesting a potential role in both plant development and stress responses. Functional validation through heterologous expression in Arabidopsis thaliana revealed that MsCCoAOMTh3 overexpression markedly increased lignin accumulation and promoted xylem development in roots. Furthermore, transgenic lines displayed enhanced drought tolerance, characterized by elevated antioxidant enzyme activity and reduced malondialdehyde (MDA) levels. Collectively, these findings suggest that MsCCoAOMTh3 acts as a positive regulator of root lignification and enhances drought tolerance by modulating both stress-responsive and lignin biosynthesis-related genes. MsCCoAOMTh3 acts as a positive regulator of root lignification and enhances drought tolerance by modulating both stress-responsive and lignin biosynthesis-related genes.