Zugl.: München, Techn. Universiẗat, Diss., 2009.

The trichothecene mycotoxins are secondary metabolites produced by a variety of fungal genera including Fusarium, Myrothecium, Trichothecium, and Stachybotyris, that are toxic to humans and animals that ingest them by consumption of contaminated grain. This work details the characterization of a novel regulatory gene from Fusarium sporotrichioides, Tri10, which is located in the trichothecene gene cluster. Northern analysis of Tri10 deletion strains, Tri10 overexpressing strains, and a Tri6 deletion strain indicated that Tri10 is required for wild-type trichothecene gene expression and for wild-type expression of a primary metabolic gene, Fpps. Analysis of these mutants also provided evidence for a regulatory feedback loop where Tri10 is required for the expression of Tri6 and Tri6 negatively regulates Tri10. Furthermore, under certain growth conditions the sensitivity of ΔTri10 and ΔTri6 strains to T-2 toxin was increased. Analysis of mutants altered in the expression and genomic position of Tri10 revealed that placing Tri10 under the control of an exogenous promoter resulted in the overexpression of Tri10 and the other Tri genes whether this construct was located inside or outside of the Tri gene cluster. Work outside of this study has shown that in addition to Fpps, three other primary metabolic genes from the isoprenoid pathway feeding into trichothecene biosynthesis (Acat, Mk, Hmgs) are also influenced by the expression of Tri10 and Tri6. In the present study, targeted cDNA microarrays were used in conjunction with multiple mutants to reveal a large group of genes, containing both trichothecene and primary metabolic genes, which were positively influenced by Tri10 expression. At the same time, a small group of genes negatively influenced by Tri10 expression was observed. These results were in agreement with observations made outside of this study and validated the use of targeted cDNA microarrays for further studies. Additional analysis of the regulatory network linking trichothecene secondary metabolism and isoprenoid primary metabolism revealed that in a mutant blocked in the first step of the pathway, and therefore in the absence of trichothecene production, this regulatory link is mediated by Tri10 and Tri6.

Thesis (doctoral)--Universität Hohenheim, 2000.

Thesis (Ph. D.)--Swedish University of Agricultural Sciences, 2001. / Includes bibliographical references.

Hohenheim, Univ., Diss., 2002.

著作権情報を一部追加（2023-06-30） / 京都大学 / 新制・論文博士 / 博士(農学) / 乙第13508号 / 論農博第2906号 / 新制||農||1095(附属図書館) / 学位論文||R4||N5408(農学部図書室) / (主査)教授 谷 史人, 教授 入江 一浩, 教授 井上 和生 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Fusarium graminearum est un champignon filamenteux qui parasite les plantes céréalières et le maïs et provoque la fusariose de l’épi. Durant l’infection, ce champignon produit des mycotoxines de la famille des trichothécènes qui s’accumulent dans les grains. Les processus de décontamination existants ne permettent pas d’éliminer complètement les trichothécènes. Ainsi, le meilleur moyen pour éviter leur accumulation dans les grains serait de pouvoir limiter leur occurrence au champ en contrôlant leur biosynthèse. Bien que la voie de biosynthèse des trichothécènes et les gènes Tri qui y sont impliqués soient bien décrits, les connaissances de base sur les mécanismes de régulation de ces gènes restent trop restreintes.Dans la première partie de ce travail, l’effet du pH sur la régulation des gènes Tri et la production de trichothécène a été étudié. En premier lieu, nous avons démontré que, in vitro, un pH acide joue le rôle d’inducteur alors qu’un pH neutre ou alcalin bloque l’expression des gènes Tri et la production de trichothécène. Ensuite, FgPac1, l’homologue du gène pacC/RIM101 codant le facteur de régulation par le pH chez les champignons a été identifié dans le génome de F. graminearum. A l’aide de souches recombinantes, nous avons démontré que la forme mature de ce facteur réprime l’expression des gènes Tri à pH acide et réduit la virulence du champignon lors de l’infection d’épis de blé. Enfin, le transcriptome de F. graminearum en réponse au pH et le rôle de Pac1 dans cette réponse a été analysé.Dans la deuxième partie de ce travail, le gène velvet sensible à la lumière, a été identifié chez F. graminearum. Ce gène constitue la composante clef d’un complexe qui coordonne la perception de la lumière avec le développement mais aussi avec le métabolisme secondaire chez les champignons. L’inactivation de FgVe1 chez F. graminearum nous a permis de démontrer son rôle dans le développement et la production de spores. Elle a montré aussi que ce gène est nécessaire pour permettre l’expression des gènes Tri, la production de trichothécène et la pathogénicité in planta.L’ensemble de ce travail permet de mieux comprendre la régulation de la production de trichothécène chez F. graminearum et ouvre des perspectives qui permettront sans doute, à long terme, d’élaborer des stratégies de lutte contre l’accumulation de trichothécène au champ. / The filamentous fungus Fusarium graminearum infects cereals plants and corn and causes “Fusarium Head Blight”. During infection, it produces mycotoxins belonging to trichothecenes family which accumulate in the grains. The available decontamination processes do not fully eliminate the trichothecene. Hence, the best way to avoid their occurrence in the grains is to limit their accumulation in the field by controlling their biosynthesis. Although the Tri genes implicated in the trichothecene biosynthetic pathway are well described, the basic knowledge regarding their regulation is still too limited.In the first part of this work, the effect of the pH on Tri genes regulation and trichothecene production was studied. First, we demonstrated that, in vitro, acidic pH acts as an inducer while a neutral or alkaline pH blocks Tri genes expression and trichothecene production. Then, FgPac1, the homologue of the pacC/RIM101 gene encoding the fungal pH regulatory factor was identified. Using recombinant strains, we demonstrated that the mature form of this factor represses Tri gene expression at acidic pH and reduces virulence during infection of wheat spikes. Finally, we analyzed the transcriptome of F. graminearum in response to pH and investigated the role of Pac1 in this response.In the second part of this work, the light-responsive velvet gene was identified in F. graminearum. This gene is the key component of a complex coordinating light perception with development and secondary metabolism in fungi. The disruption of FgVe1 in F. graminearum demonstrated its role in development and spores production. It also showed that this gene is necessary for Tri gene expression, trichothecene production and pathogenicity in planta.Overall, this work allows a better understanding of trichothecene regulation in F. graminearum and provides novel perspectives to develop new strategies against trichothecene accumulation during cereal growing in the field.

Hohenheim, Univ., Diss., 2004.

No description available.