Magnaporthe oryzae Transcription Factor MoBZIP3 Regulates Appressorium Turgor Pressure Formation during Pathogenesis.

The devastating fungus Magnaporthe oryzae ( M. oryzae ) forms a specialized infection structure known as appressorium, which generates enormous turgor, to penetrate the plant cells. However, how M. oryzae regulates the appressorium turgor formation, is not well understood. In this study, we identified Mo B ZIP3 , a bZIP transcription factor that functioned in pathogenesis in M. oryzae . We found that the pathogenicity of the Mo B ZIP3 knockout strain (Δ mo b zip3 ) was significantly reduced, and the defect was restored after re-expression of Mo B ZIP3 , indicating that Mo B ZIP3 is required for M. oryzae virulence. Further analysis showed that Mo B ZIP3 functions in utilization of glycogen and lipid droplets for generation of glycerol in appressorium. Mo B ZIP3 localized in the nucleus and could bind directly to the promoters of the glycerol synthesis-related genes, MoPTH2 , MoTGL1 and MoPEX6 , and regulate their expression which is critical for glycerol synthesis in the appressorium turgor pressure generation. Furthermore, the critical turgor sensor gene MoSln1 was also down regulated and its subcellular localization was aberrant in Δ mo b zip3 , which leads to a disordered actin assembly in the Δ mo b zip3 appressorium. Taken together, these results revealed new regulatory functions of the bZIP transcription factor MoBZIP3, in regulating M. oryzae appressorium turgor formation and infection.