Protein kinase FgSch 9 serves as a mediator of the target of rapamycin and high osmolarity glycerol pathways and regulates multiple stress responses and secondary metabolism in F usarium graminearum

Abstract

Summary S accharomyces cerevisiae protein kinase Sch 9 is one of the downstream effectors of the target of rapamycin ( TOR ) complex 1 and plays multiple roles in stress resistance, longevity and nutrient sensing. However, the functions of Sch 9 orthologs in filamentous fungi, particularly in pathogenic species, have not been characterized to date. Here, we investigated biological and genetic functions of FgSch 9 in F usarium graminearum . The FgSCH 9 deletion mutant (Δ FgSch 9) was defective in aerial hyphal growth, hyphal branching and conidial germination. The mutant exhibited increased sensitivity to osmotic and oxidative stresses, cell wall‐damaging agents, and to rapamycin, while showing increased thermal tolerance. We identified FgMaf1 as one of the FgSch 9‐interacting proteins that plays an important role in regulating mycotoxin biosynthesis and virulence of F . graminearum . Co‐immunoprecipitation and affinity capture‐mass spectrometry assays showed that FgSch 9 also interacts with FgTor and FgHog 1. More importantly, both Δ FgSch 9 and FgHog 1 null mutant (Δ FgHog 1) exhibited increased sensitivity to osmotic and oxidative stresses. This defect was more severe in the FgSch 9/ FgHog 1 double mutant. Taken together, we propose that FgSch 9 serves as a mediator of the TOR and high osmolarity glycerol pathways, and regulates vegetative differentiation, multiple stress responses and secondary metabolism in F . graminearum .

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