Single-repeat MYB transcription factor, OsMYB1R, enhanced phytoalexin sakuranetin accumulation and Magnaporthe oryzae resistance

Sakuranetin, a flavonoid phytoalexin in rice, plays a crucial role in defense against pathogen infection. While MYB-type transcription factors are well-known to regulate plant growth, development, secondary metabolism, and adaptation to environmental stresses, the function of rice MYB-related transcription factors in sakuranetin biosynthesis and sakuranetin-mediated defense remains unclear. In this study, we identified and characterized OsMYB1R, a novel single repeat MYB transcription factor that acts as a transcriptional activator in sakuranetin biosynthesis. Protein-DNA binding and activation assays revealed that OsMYB1R directly regulates the gene promoter of OsNOMT, a key enzyme in sakuranetin synthesis. Molecular analyses and infection studies using OsMYB1R-overexpressing (OsMYB1R-OE) and OsMYB1R-knockout (Osmyb1r, generated using CRISPR/Cas9) plants demonstrated that OsMYB1R increases sakuranetin production and decreases Magnaporthe oryzae infection by transcriptionally regulating OsNOMT expression. This finding indicates a positive regulation of sakuranetin biosynthesis and antifungal resistance by the OsMYB1R-OsNOMT crosstalk. Interestingly, the alteration of OsMYB1R expression did not affect yield-related agronomic traits. Our results reveal a novel and positive role of 1R-MYB in secondary metabolite biosynthesis and pathogen defense, suggesting that OsMYB1R is a potential gene for effectively enhancing rice resistance without compromising yield.