MYB gene family in Magnolia biondii: Identification and functional roles in waterlogging stress response

Magnolia biondii, a deciduous tree of the Magnoliaceae family, is economically important for landscaping and medicine. However, its fleshy roots are highly sensitive to waterlogging, restricting expansion of cultivation area. MYB transcription factors play critical roles in plant abiotic stress response, while their detailed functions in M. biondii have not been systematically investigated. In this study, 185 MbMYBs were identified in M. biondii genome. Transcriptomic data of waterlogged roots revealed that most of MbMYBs were down-regulated and severe waterlogging induced more differentially expressed MbMYBs than moderate waterlogging. Notably, 113 MbMYBs were identified in M. biondii roots as waterlogging-responsive MbMYBs, including 42 Mb1R-MYBs, 68 MbR2R3-MYBs, and 3 Mb3R-MYBs. In particular, five consistently up-regulated MbMYBs were considered as key regulators in response to waterlogging stress. Collinearity analysis revealed that 113 waterlogging-responsive MbMYBs exhibited closer relationship with MYBs in basal angiosperms, and 45 of them were generated by gene duplication events under purifying selection. In addition, multiple stress- and hormone-responsive cis-elements were identified in the promoter regions of 113 waterlogging-responsive MbMYBs, which may confer their potential roles in stress response. Functional validation demonstrated that, under waterlogging stress, transgenic plants overexpressing MbMYB146 and MbMYB155 exhibited lower levels of H₂O₂ and MDA, along with more stable antioxidant enzyme activities. These findings suggest that MbMYB146 and MbMYB155 enhance waterlogging tolerance by maintaining ROS homeostasis through enzymatic antioxidant systems, thereby alleviating lipid peroxidation. Overall, our results provide preliminary insights into the role of MbMYBs in waterlogging stress responses and lay a foundation for the molecular breeding and genetic improvement of M. biondii.