AtMYB44 positively modulates disease resistance to Pseudomonas syringae through the salicylic acid signalling pathway in Arabidopsis

Plant MYB transcription factors are implicated in resistance to biotic and abiotic stresses. Here, we demonstrate that an R2-R3 MYB transcription factor, AtMYB44, plays a role in the plant defence response to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (PstDC3000). The expression of AtMYB44 was upregulated upon pathogen infection and treatments with defence-related phytohormones. Transgenic plants overexpressing AtMYB44 (35S-Ms) exhibited greater levels of PR1 gene expression, cell death, callose deposition and hydrogen peroxide (H2O2) accumulation in leaves infected with PstDC3000. Consequently, 35S-M lines displayed enhanced resistance to PstDC3000. In contrast, the atmyb44 T-DNA insertion mutant was more susceptible to PstDC3000 and exhibited decreased PR1 gene expression upon infection. Using double mutants constructed via crosses of 35S-M lines with NahG transgenic plants and nonexpressor of pathogenesis-related genes1 mutant (npr1–1), we demonstrated that the enhanced PR1 gene expression and PstDC3000 resistance in 35S-M plants occur mainly through the salicylic acid signalling pathway.