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

Abstract

<i>Fusarium asiaticum</i> belongs to one of the phylogenetical subgroups of the <i>F. graminearum</i> species complex and is epidemically predominant in the East Asia area. The life cycle of <i>F. asiaticum</i> is significantly regulated by light. In this study, the fungal blue light receptor white collar complex (WCC), including FaWC1 and FaWC2, were characterized in <i>F. asiaticum</i>. The knockout mutants Δ<i>Fawc1</i> and Δ<i>Fawc2</i> 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 <i>F. asiaticum</i>. Unexpectedly, however, the functions of <i>Fawc1</i> and <i>Fawc2</i> diverged in regulating virulence, as the Δ<i>Fawc1</i> was avirulent to the tested host plant materials, but Δ<i>Fawc2</i> 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 <i>F. asiaticum</i> 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.