Mechanism Of STRIPAK Complex For Regulating Sexual Development And Pathogenicity In Fusarium Graminearum

Fusarium head blight(FHB)caused by Fusarium complex is one of the most serious wheat diseases in China.In addition to severe yield losses,the pathogens produce mycotoxins such as deoxynivalenol(DON)to pollute the grains that poses a serious threat to human and animal health.A thorough understanding of the fungal pathogenicity,DON biosynthesis and epidemic in Fusarium graminearum is essential for developing new approaches to control FHB and DON contamination.The perithecium is the main form of the pathogen overwintering,and ascospore is the primary inoculum of FHB in field.The deciphering of the molecular mechanism of sexual development will provide a theoretical foundation for the prevention and control of FHB by reducing primary inoculum.Our previous study showed that FgPpg1,the downstream phosphatase of TOR(target of rapamycin)signaling pathway,is critical to the sexual development of Fusarium graminearum.However,the regulatory mechanism is still unknown.In this study,we found that FgPpg1 is one of components in STRIPAK(striatin-interacting phosphatase and kinase)complex that regulate the sexual development and pathogenicity in Fusarium graminearum.The results showed that:1)Rapamycin stimulated the perithecium formation of Fusarium graminearum on carrot agar plates,compared with that upon control treatment and carbendazim.Further investigation indicated that induction of the perithecium formation upon rapamycin was largely depended on the FgTap42-FgPpg1/FgSit4 signaling branch in the TOR pathway,but not FgSch9.2)The yeast two-hybrid,coimmunoprecipitation and affinity capture-mass spectrometry analyses strongly indicated that FgPpg1,FgHam2,FgHam3,FgHam4,FgPP2 AA and FgMob3 interacted with each other and formed a conserved STRIPAK complex.Moreover,FgHam2,FgHam3 and FgPpg1 interacted with FgTap42 directly.3)Disruption of STRIPAK complex totally abolished the perithecium formation on carrot agar plates and sterilized wheat straw.Among them,the phosphatase activity of FgPpg1 was essential for sexual development.Further investigation revealed that STRIPAK complex regulated the subcellular localization of FgMgv1 and expression of key genes for sexual development.Mutants of the complex reduced the nuclear accumulation of FgMgv1 and resulted in the low expression level of sexual development related genes.4)Furthermore,the STRIPAK complex was also involved in the fungal pathogenicity.The deletion of STRIPAK complex resulted in decreased penetration ability,reduction of DON production,and increased sensitivities towards all tested biotic stresses,including cell wall,oxidative stress and phytoalexin.In addition to growth defects,all above phenotypes contributed to the attenuated virulence of STRIPAK mutants on host plants.Taken together,results in this study suggested that STRIPAK complex regulated the fungal sexual development,pathogenicity,mycotoxin biosynthesis and environmental adaptation under regulated by TOR signaling pathway in Fusarium graminearum.