White Collar 1 Modulates Oxidative Sensitivity and Virulence by Regulating the HOG1 Pathway in Fusarium asiaticum

Fusarium asiaticum is an epidemiologically important pathogen of cereal crops in east Asia, accounting for both yield losses and mycotoxin contamination problems in food and feed products. FaWC1, a component of the blue-light receptor White Collar complex (WCC), relies on its transcriptional regulatory zinc finger domain rather than the light-oxygen-voltage domain to regulate pathogenicity of F. asiaticum, although the downstream mechanisms remain obscure. In this study, the pathogenicity factors regulated by FaWC1 were analyzed. It was found that loss of FaWC1 resulted in higher sensitivity to reactive oxygen species (ROS) than in the wild type, while exogenous application of the ROS quencher ascorbic acid restored the pathogenicity of the ΔFawc1 strain to the level of the wild type, indicating that the reduced pathogenicity of the ΔFawc1 strain is due to a defect in ROS tolerance. Moreover, the expression levels of the high-osmolarity glycerol (HOG) mitogen-activated protein kinase (MAPK) pathway genes and their downstream genes encoding ROS scavenging enzymes were downregulated in the ΔFawc1 mutant. Upon ROS stimulation, the FaHOG1-green fluorescent protein (GFP)-expressing signal driven by the native promoter was inducible in the wild type but negligible in the ΔFawc1 strain. Overexpressing Fahog1 in the ΔFawc1 strain could recover the ROS tolerance and pathogenicity of the ΔFawc1 mutant, but it remained defective in light responsiveness. In summary, this study dissected the roles of the blue-light receptor component FaWC1 in regulating expression levels of the intracellular HOG-MAPK signaling pathway to affect ROS sensitivity and pathogenicity in F. asiaticum. IMPORTANCE The well-conserved fungal blue-light receptor White Collar complex (WCC) is known to regulate virulence of several pathogenic species for either plant or human hosts, but how WCC determines fungal pathogenicity remains largely unknown. The WCC component FaWC1 in the cereal pathogen Fusarium asiaticum was previously found to be required for full virulence. The present study dissected the roles of FaWC1 in regulating the intracellular HOG MAPK signaling pathway to affect ROS sensitivity and pathogenicity in F. asiaticum. This work thus extends knowledge of the association between fungal light receptors and the intracellular stress signaling pathway to regulate oxidative stress tolerance and pathogenicity in an epidemiologically important fungal pathogen of cereal crops.