Characterization of genes related to heat shock response in Fusarium graminearum

Abstract

The Fusarium head blight primarily caused by ascomycete Fusarium graminearum leads to severe yield losses of various cereal crops and contamination of grains with mycotoxins that are harmful to humans and livestock. The heat shock response involves the induction of a defined set of heat shock proteins which promote the folding of client proteins or target aggregated proteins for degradation, therefore affecting the diverse cellular processes in eukaryotes. In this study, genome-wide transcriptome analysis of cellular adaptation to thermal stress was performed in F. graminearum. We found that profound alterations in gene expression were required for heat shock response in F. graminearum. Heat shock protein 90 (FgHsp90) played a central role in heat shock response and FgHsp90 was exclusively localized to nuclei in response to heat stress. Moreover, the comprehensive functional characterization of FgHsp90 provides clear genetic evidences supporting its crucial roles in vegetative growth, reproduction, and virulence of F. graminearum. Next, the FgNot3 subunit of the Ccr4-Not complex, evolutionarily conserved from yeast to human, was investigated in this fungus. FgNot3 had numerous functions in fungal morphogenesis, sporulation, and virulence. We found that FgNot3 functions as a negative regulator of the production of secondary metabolites, including trichothecenes and zearalenone. Numerous defects of Fgnot2 and Fgnot4 deletion mutants, other subunit mutants of the Ccr4-Not complex, demonstrated that the Not module of the Ccr4-Not complex is conserved, and each subunit not only primarily functions within the context of a complex, but also might have distinct roles outside of the complex in F. graminearum. This is the first study to functionally characterize the Hsp90 and the Ccr4-Not complex in plant pathogenic fungi and provides novel insights into signal transduction pathways in fungal development.