The Photoreceptor Components FaWC1 and FaWC2 of Fusarium asiaticum Cooperatively Regulate Light Responses but Play Independent Roles in Virulence Expression

Fusarium asiaticum belongs to one of the phylogenetical subgroups of the F. graminearum species complex and is epidemically predominant in the East Asia area. The life cycle of F. asiaticum is significantly regulated by light. In this study, the fungal blue light receptor white collar complex (WCC), including FaWC1 and FaWC2, were characterized in F. asiaticum. The knockout mutants Delta Fawc1 and Delta Fawc2 were generated by replacing the target genes via homologous recombination events. The two mutants showed similar defects in light-induced carotenoid biosynthesis, UV-C resistance, sexual fruiting body development, and the expression of the light-responsive marker genes, while in contrast, all these light responses were characteristics in wild-type (WT) and their complementation strains, indicating that FaWC1 and FaWC2 are involved in the light sensing of F. asiaticum. Unexpectedly, however, the functions of Fawc1 and Fawc2 diverged in regulating virulence, as the Delta Fawc1 was avirulent to the tested host plant materials, but Delta Fawc2 was equivalent to WT in virulence. Moreover, functional analysis of FaWC1 by partial disruption revealed that its light-oxygen-voltage (LOV) domain was required for light sensing but dispensable for virulence, and its Zinc-finger domain was required for virulence expression but not for light signal transduction. Collectively, these results suggest that the conserved fungal blue light receptor WCC not only endows F. asiaticum with light-sensing ability to achieve adaptation to environment, but it also regulates virulence expression by the individual component FaWC1 in a light-independent manner, and the latter function opens a way for investigating the pathogenicity mechanisms of this important crop disease agent.