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Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/7/2014 Publication Date: 8/1/2014 Citation: Brown, D.W., Busman, M., Proctor, R. 2014. Fusarium verticillioides SGE1 is required for full virulence and regulates expression of protein effector and secondary metabolite biosynthetic genes. Molecular Plant-Microbe Interactions. 27(8):809-823. Interpretive Summary: This research identified a gene in the fungus Fusarium that controls both toxin production and the ability of the fungus to cause disease. Fusarium is of concern to agriculture and food and feed safety, because it is a worldwide cause of the crop disease corn ear rot, and it can contaminate corn kernels, as well as food/feed derived from them, with the cancer-causing toxins fumonisins. Fungi often have master regulatory genes that control multiple biological processes, including the ability to cause diseases in animals or plants or to produce toxins. In this research, we identified a regulatory gene in Fusarium and demonstrated that the gene controls the ability to cause disease of corn and produce fumonisins. The results also indicate that this gene controls whether hundreds of other Fusarium genes are active or inactive. Based on DNA sequence analysis, the predicted functions of these other genes vary from enabling the fungus to sense changes in its environment to inducing physiological changes in plants. This research provides a foundation for understanding the biological processes that are required for Fusarium to cause crop diseases and produce toxins. This information will be of use to plant pathologists, plant breeders, and other scientists working to develop strategies that reduce diseases and toxin contamination of crops. Technical Abstract: The transition from one lifestyle to another in some fungi is initiated by a single orthologous gene, SGE1 in Fusarium oxysporum, that regulates markedly different gene sets in different fungi. Despite these differences, many of the regulated genes affect pathogenicity as they encode effector proteins or proteins involved in the synthesis of secondary metabolites (SMs). Fusarium verticillioides is both an endophyte and a pathogen of maize and can grow as a saprophyte on dead plant material in the soil. During growth on live maize plants, it can synthesize a number of toxic SMs including fumonisins, fusarins, and fusaric acid, which can contaminate kernels and food and feed derived from them. In this study, the role of F. verticillioides SGE1 in pathogenicity was examined by gene deletion analysis and transcriptomics. FvSGE1 is not required for vegetative growth or conidiation but is required for wild-type pathogenicity and affects the synthesis of multiple SMs including fumonisins and fusarins. Induced expression of FvSGE1 altered expression of hundreds of genes, including numerous putative effector genes that could contribute to growth in planta, genes encoding cell surface proteins, gene clusters involved in synthesis of fusarins, bikaverin and an unknown metabolite, as well as the gene (FvFUM21) encoding the fumonisin pathway specific transcriptional regulator. Despite a global regulatory role for FvSGE1, the ability of sge1 mutants to cause some seedling disease and synthesize significant amounts of fumonisins attest to the importance of other factors regulating these processes and their elucidation. |
