PagMYB147 confers resilience 84 K poplar to Melampsora magnusiana by regulating the transcription of PagCHI5

Melampsora is the main pathogen of poplar leaf rust, which severely damages poplar leaves. R2R3-MYB transcription factors play an important role in plant resistance to biotic stresses. We previously showed that the R2R3-MYB transcription factor PagMYB147 is up-regulated expression during M. magnusiana ( Mmag ) infection and positively regulates resistance to Mmag in poplar. However, the transcriptional regulatory function of PagMYB147 in poplar- Mmag interactions is not yet known. In this study, pagmyb147 mutant poplar plants exhibited reduced resistance to Mmag . PagMYB147 targeted the promoter of the chitinase gene PagCHI5 and activates its transcription. Overexpression of PagCHI5 poplar plants enhanced resistance to Mmag , indicating a positive role of PagCHI5 in poplar resistance. After Mmag infection in vivo, the pagmyb147 mutant reduced total chitinase activity. Taken together, our results suggest that PagMYB147 confers resistance to leaf rust by increasing total chitinase activity in poplar. The manuscript presents a comprehensive study on how the R2R3-MYB transcription factor PagMYB147 enhances poplar resistance to rust through direct transcriptional regulation of the chitinase gene PagCHI5. The highlights emphasize the novel regulatory mechanism, the direct protein-DNA interaction, the functional validation through overexpression and gene editing, and the broader implications for understanding multi-pathway plant defense responses. After Mmag infection, transcription of PagMYB147 is induced and positively regulates expression of PagCHI5 by binding to its promoter (curved arrow) and activating transcription. As a result, the chitinase activity is increased in vivo. In short, PagMYB147 increased resistance to Mmag infection in the poplar. • The R2R3-MYB transcription factor PagMYB147 positively regulates 84 K poplar resistance to Melampsora magnusiana through transcriptional activation. • PagMYB147 directly binds to the ATAACGGT motif in the PagCHI5 promoter and activates its transcription, as confirmed by EMSA, Y1H, and dual luciferase assays. • Overexpression of PagCHI5 significantly enhanced poplar resistance to M. magnusiana , while pagmyb147 mutants showed reduced chitinase activity and increased susceptibility. • Gene editing of PagMYB147 using CRISPR/Cas9 resulted in mutant plants with significantly increased uredinia density and fungal biomass compared to wild-type controls. • PagMYB147 confers rust resistance through both chitinase-mediated chitin degradation and regulation of other defense signaling pathways (ROS, SA, and JA).