MYB Transcription Factors in Plant Responses to Biotic and Abiotic Stresses: Regulatory Mechanisms, Experimental Evidence, and Prospects for Crop Improvement

MYB transcription factors, named after the v-MYB oncogene of avian myeloblastosis virus, constitute one of the largest and most functionally diverse transcription factor families in plants, contributing to growth, development, and environmental adaptation. This review synthesizes current knowledge of MYB-associated responses to biotic and abiotic stresses, including pathogen infection, insect herbivory, salinity, drought, temperature extremes, UV-B radiation, and nutrient deficiency. MYB transcription factors may preserve membrane integrity, photosynthesis, and cellular function by coordinating redox homeostasis, antioxidant defense, and metabolic responses, although physiological outcomes and supporting evidence vary across MYB factors and stress conditions. We discuss the molecular processes through which MYB proteins influence stress responses, with particular attention to phytohormone signaling, reactive oxygen species homeostasis, secondary metabolism, cell-wall remodeling, ion transport, and immune regulation. Importantly, we distinguish directly demonstrated molecular interactions and transcriptional regulatory mechanisms from genetic phenotypes, heterologous expression results, and associations inferred from transcriptomic, metabolomic, or physiological analyses. We also examine the extent to which reported MYB functions have been validated in crop species, highlighting the distinction between endogenous gene function and phenotypes obtained in heterologous systems. Finally, we discuss outstanding challenges in resolving MYB-mediated responses to combined stresses, identifying functional natural variants, and translating experimentally validated regulatory mechanisms into crop improvement. This evidence-oriented synthesis provides a basis for evaluating the biological significance of MYB-associated stress responses and their potential applications in developing stress-resilient crops.