Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/24/2013
Publication Date: 7/19/2013
Citation: Kim, H.-K., Lee, S., Jo, S.-M., McCormick, S.P., Butchko, R.A.E., Proctor, R.H., Yun, S.-H. 2013. Functional roles of FgLaeA in controlling secondary metabolism, sexual development, and virulence in Fusarium graminearum. PLoS One. 8(7):e68441. Interpretive Summary: Trichothecenes are toxic substances produced by the wheat disease fungus Fusarium graminearum. We are interested in reducing or eliminating these toxins from wheat. In an effort to accomplish that goal, we need to understand the biology of the fungus with regard to trichothecene production. In this study, we found that in F. graminearum, the gene laeA turns on the genes that control the production of trichothecenes and other mycotoxins, the sexual and asexual development of the fungus, and its ability to cause plant disease. Knocking out this gene greatly reduced both toxin production and disease symptoms. A better understanding of this type of global control may lead to novel strategies for reducing or eliminating these toxins from wheat.
Technical Abstract: Fusarium graminearum, the causal agent of Fusarium head blight in cereal crops, produces mycotoxins such as trichothecenes and zearalenone in infected plants. Here, we focused on the function of FgLaeA in F. graminearum, a homolog of Aspergillus nidulans LaeA encoding the global regulator for both secondary metabolism and sexual development. Prior to gene analysis, we constructed a novel luciferase reporter system consisting of a transgenic F. graminearum strain expressing a firefly luciferase gene under control of the promoter for either TRI6 or ZEB2 controlling the biosynthesis of these mycotoxins. Targeted deletion of FgLaeA led to a dramatic reduction of luminescence in reporter strains, indicating that FgLaeA controls the expression of these transcription factors in F. graminearum; reduced toxin accumulation was further confirmed by GC-MS analysis. Overexpression of FgLaeA caused the increased production of trichothecenes and additional metabolites. RNA seq-analysis revealed that gene member(s) belonging to ~70% of total tentative gene clusters, which were previously proposed, were differentially expressed in the 'FgLaeA strain. In addition, 'FgLaeA strains exhibited an earlier induction of sexual fruiting body (perithecia) formation and drastically reduced disease symptoms in wheat, indicating that FgLaeA seems to negatively control perithecial induction, but positively control virulence toward host plant. FgLaeA was constitutively expressed under both mycotoxin production and sexual development conditions. Overexpression of a GFP-FgLaeA fusion construct in the 'FgLaeA strain restored all phenotypic changes to wild-type levels and led to constitutive expression of GFP in both nuclei and cytoplasm at different developmental stages. A split luciferase assay demonstrated that FgLaeA was able to interact with FgVeA, a homolog of A. nidulans veA. Taken together, these results demonstrate that FgLaeA, a member of putative FgVeA complex, controls secondary metabolism, sexual development, and virulence in F. graminearum, although the specific regulation pattern differs from that of LaeA in A. nidulans.