Loss-of-function of VrMYB104 in Mungbean hampers growth and multiple adaptive responses under waterlogging stress.

Abstract

Key message: VrMYB104, a R2R3 MYB transcription factor, plays a key role in mungbean's waterlogging stress tolerance by modulating oxidative, osmotic, and hypoxia responsive genes' expression. In tropical and subtropical areas, mungbean (Vigna radiata) is an essential legume crop; however, waterlogging stress poses a serious threat to its productivity. Plant stress responses are known to be regulated by R2R3 MYB transcription factors (TFs). Little is known about their functional roles in mungbean under waterlogging stress. In this study, we identified 70 R2R3 type MYB TFs, through a genome-wide identification in mungbean which were characterized in-silico using bioinformatic analyses, such as chromosomal distribution, promoter cis-element prediction, motif structure, and phylogeny. VrMYB104 was selected for functional validation under waterlogging stress based on promoter analysis and spatio-temporal studies. Loss-of-function analysis using virus-induced gene silencing (VIGS) revealed growth retardation and yield reduction in silenced plants. Biochemical assays under waterlogging stress showed decreased proline levels, reduced activities of antioxidant enzymes (SOD, APX, CAT), and elevated reactive oxygen species (ROS), indicating impaired oxidative and osmotic stress responses. Expression profiling further revealed upregulation of PDC and LDH and downregulation of ACS, suggesting that VrMYB104 coordinates fermentative metabolism and hormonal signaling under stress. Collectively, these results establish VrMYB104 as a critical regulator of multiple stress-response pathways and highlight its potential for developing waterlogging-tolerant mungbean cultivars.