Biological roles of Phytophthora infestans PiSAK1

Abstract:

[Background] Phytophthora infestans is a major pathogen causing potato late blight. Stress-activated protein kinases (SAPKs), a class of mitogen-activated protein kinases (MAPKs), play a role in regulating cell responses of fungi to external stress factors. The biological functions of a SAPK in P. infestans, i.e., PiSAK1, remain unknown. [Objective] To explore the biological roles of PiSAK1 in the growth and development, the responses to external stress factors, and the infection in potato. [Methods] The bioinformatics tools were used to characterize PiSAK1. The expression levels of PiSAK1 at different development and infection stages were determined by RT-qPCR. Finally, the PiSAK1-silenced and-overexpressed strains were constructed and characterized. [Results] PiSAK1 had a typical Ser/Thr protein kinase catalytic domain of MAPKs and shared the same evolutionary branch with the SAPKs of other oomycetes. The expression level of PiSAK1 was the highest at the stage of cysts or 48 h after infecting potato. Moreover, it was significantly up-regulated after exposure to 0.3 mol/L NaCl or 3 mmol/L H₂O₂ for 0.5 h. The results showed that the PiSAK1-silenced strains were significantly weaker than the wild type in terms of colony growth, sporangium production, resistance to NaCl and H₂O₂, scavenging of reactive oxygen species, and pathogenicity. However, the PiSAK1-overexpressed strains showed significantly enhanced phenotypic characteristics compared with the wild type, except for no significant difference in colony growth. [Conclusion] PiSAK1 plays a role in the growth and development, osmotic regulation, oxidative stress response, and infection in potato. Our results provide a theoretical basis for further research on new targets of fungicides and breeding of resistant potato varieties.