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

Ying Tang,Zhengyu Lu,Pinkuan Zhu,Ling Xu,Li Huang,Haozhen Nie,Yiwen Wang,Yina Jiang,Yao Qu,Ni Zheng

doi:10.3390/microorganisms8030365

Abstract

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 ΔFawc1 and ΔFawc2 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 ΔFawc1 was avirulent to the tested host plant materials, but ΔFawc2 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.

Highlights

Fusarium head blight (FHB), which is usually caused by the pathogen Fusarium graminearum, is known as a global problem devastating small grain cereal crops [1]
Since F. asiaticum belongs to a sub-lineage of the Fusarium graminearum species complex, the orthologous genes of wc1 and wc2 in F. asiaticum, namely Fawc1 and Fawc2, were identified as follows: BLASTP search of the F. gaminearum genome in Ensembl Fungi database, using the amino acid sequences of Neurospora crassa white-collar 1 protein (WC-1) (NCU02356) and WC-2 (NCU00902) proteins [34] as queries, resulted in the corresponding orthologs namely FgWC1 (FGSG_07941) and FgWC2 (FGSG_00710), respectively
The corresponding genes and their flanking sequences were used as references to design specific primers to amplify the open reading frame (ORF) sequences of their orthologs, Fawc1 and Fawc2, in F. asiaticum strain EXAP-08 via the Pfu DNA polymerase

Summary

Introduction

Fusarium head blight (FHB), which is usually caused by the pathogen Fusarium graminearum, is known as a global problem devastating small grain cereal crops [1]. Besides being commonly associated with FHB, F. asiaticum has been found to cause postharvest rot on asparagus spears and produce 3A-DON mycotoxin during host infection [10]. Introgression of the disease resistance genes identified in natural sources into elite cultivars represents a reliable route for plant disease management [11]. Plant sources for FHB resistance are limited, and no fully resistant cultivars are yet available [12]. Controlling FGSC-caused diseases will benefit from an in-depth understanding of how the pathogens infect and spread inside the host. The molecular mechanism of development and virulence regulation is less known in F. asiaticum than in F. graminearum, there is an ongoing trend in which F. asiaticum becomes more aggressive and devastating than F. graminearum in the East Asian area [6,14,16]

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