The importin α subunit PsIMPA1 mediates the oxidative stress response and is required for the pathogenicity of Phytophthora sojae

The sensing of extracellular signals and their transduction into an appropriate response are crucial for the survival and virulence of plant pathogens. Eukaryotic plant pathogens must overcome the obstacles posed by nuclear membranes to manipulate gene expression to adapt to the host challenge. A highly sophisticated mechanism is the use of importins to transport proteins into the nucleus. In this study, we identified a conserved importin α gene, PsIMPA1, in Phytophthora sojae that was differentially expressed during the life cycle of this soybean pathogen. PsIMPA1 expression was lowest in zoospores and cysts but relatively consistent during the other life cycle stages, except for a slight increase at 6 h post infection. Silenced mutants Psimpa1 had a decreased growth rate, an aberrant mycelial morphology, and a severely impaired ability to form oospores and sporangia. In addition, the Psimpa1 mutants exhibited reduced pathogenicity compared to the wild type. 3,3-Diaminobenzidine (DAB) staining and in vitro hydrogen peroxide tolerance assays showed that the scavenging of reactive oxygen species by these mutants was significantly impaired. Taken together, these results indicate that PsIMPA1 regulates multiple processes during the life cycle of P. sojae.