The velvet protein Vel1 controls initial plant root colonization and conidia formation for xylem distribution in Verticillium wilt
von Annalena Maria Höfer geb. Otto
Datum der mündl. Prüfung:2021-01-08
Erschienen:2021-08-24
Betreuer:Prof. Dr. Gerhard Braus
Gutachter:Prof. Dr. Gerhard Braus
Gutachter:Prof. Dr. Andrea Polle
Gutachter:Prof. Dr. Rolf Daniel
Dateien
Name:Dissertation Annalena Höfer.pdf
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Description:Dissertation Annalena Höfer
Zusammenfassung
Englisch
The velvet family of regulatory proteins is well-conserved in fungi and links developmental processes and secondary metabolite production. These proteins comprise a velvet domain for DNA binding and dimerization with structural similarity to the Rel homology domain of the mammalian NF-κB transcription factor. Functions of homologs of all velvet domain protein encoding genes in the fungal life cycle were systematically characterized in the plant pathogen Verticillium dahliae. These velvet proteins are required in different phases of fungal growth, development, secondary metabolite formation and pathogenicity. The Vel1-Vel2, Vel2-Vos1 and Vel3-Vos1 heterodimers are present during vegetative hyphal growth. Except from Vel3, all velvet proteins additionally interact with other non-velvet proteins. During filamentous growth Vel1, Vel3 and Vos1 are predominately localized to the nucleus. Vel2 is mainly localized to the nucleus but subpopulations are also present in the cytoplasm. The soil-borne V. dahliae plant pathogenic fungus is responsible for Verticillium wilt disease of many crops. Fungal diseases in crop plants are an emerging threat for human nutrition in connection with the increasing world population. Verticillium spp. start infection by colonizing and invading the roots. One of the major novel findings of this thesis is that the velvet domain protein Vel1 is required for the initial plant root colonization and entry into the host xylem. Inside the plant the fungus forms conidia which are distributed by the sap stream. Together with Vel3, Vel1 promotes conidiation and propagation in planta. Germinating conidia colonize the whole host and finally lead to the induction of disease symptoms. Vel1 is needed for disease symptom induction in tomatoes. In the senescent plant, the fungus forms microsclerotia as resting structures in order to survive until the next growing season. Formation of microsclerotia is positively regulated by Vel1 and in a light-dependent manner by Vel2. Vel3 has opposite functions during formation of these resting structures. Microsclerotia contain the pigment melanin. The synthesis of the melanin precursor scytalone and other secondary metabolites is promoted by Vel1 and Vel2 but negatively regulated by Vel3. So far, the function of Vos1 in V. dahliae remains ambiguous. Fungicides either harm the environment or are useless once the fungus has entered the plant xylem. Inhibition of fungal growth, conidiation and resting structure formation are strategies to combat the pathogen. Vel1 is the most important among the four V. dahliae velvet proteins with a wide variety of functions during all phases of the fungal life cycle in as well as ex planta making it a potential target to combat the fungus. A combined application with antagonistic bacteria might be a strategy to persistently harm the fungus, because we could show in pilot studies that fluorescent pseudomonads, which have the genomic requirements to produce different secondary metabolites, are able to inhibit conidia germination and growth of the plant pathogen V. dahliae in a media-dependent manner.
Keywords: Verticillium dahliae; Velvet proteins; Secondary metabolism; Root colonization; Protein-protein interaction; Plant pathogenic fungus; Microsclerotia; Conidia; Pseudomonas; 2,4-diacetylphloroglucinol; Phenazines; GacS/GacA two-component system; Aspergillus nidulans; Aspergillus fumigatus