Fungal development of Verticillium resting structures and plant infection

• Applicant: Professor Dr. Gerhard H. Braus
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 270947635

Soil-borne plant-pathogenic Verticillium dahliae fungi form melanised microsclerotia, which can rest and survive for more than a decade in the soil. Development of such dormant fungal survival structures is often linked to the biosynthesis of specific secondary metabolites. Germination of microsclerotia is triggered by root exudates of appropriate host plants, which results in directed fungal hyphal growth towards plant roots. V. dahliae colonises the root cortex and invades the vascular system. Conidiation is started in the xylem to use the sap stream for distribution of the fungus within the plant. Fungal colonisation within the host can result in disease symptoms, such as chlorosis, necrosis, stunted growth or wilting. Plant-pathogenic V. dahliae infects up to 400 plants including agriculturally important crops and causes increasing economical damage worldwide. This research project aims to characterise the complex interplay between Verticillium Vta-Som1-Velvet and unfolded protein response Hac1 transcription factors. These regulators orchestrate sequential and interconnected genetic networks for development and infection of V. dahliae through the roots into the plant xylem system. These networks, which we have identified in the first funding period, control the formation of microsclerotia as resting and survival structures in the soil. They germinate, the fungus colonises the plant and finally microsclerotia formation is initiated again at the end of the season. A detailed molecular understanding of control mechanisms, which reduce V. dahliae microsclerotia formation during fungal colonisation of host plants or in soil would be very helpful. VTA-SOM1-VELVET networks respond to the external biotic (e.g. microbiomes in rhizosphere, plant) and abiotic environment as well as to internal signalling pathways. The VTA-SOM1-VELVET networks control and adapt gene expression for the appropriate fungal reply in growth, defense, development or secretion. We will analyse (i) how the different V. dahliae VTA-SOM1-VELVET gene networks are coordinated and connected and which genes are directly controlled by specific transcription factors. We will (ii) determine posttranslational modifications including phosphorylation and ubiquitination/deubiquitination and examine protein stability control mechanisms of transcription factors of the VTA-SOM1-VELVET genetic networks and their impact on fungal development and virulence. We will use a combination of genetic, cell biological, proteomic, metabolomic as well as pathogenicity experiments including for example the generation and investigation of deletion strains, GFP-pulldown, ChIPSeq, root and plant infection. Our goal is the detailed understanding of molecular control steps required for microsclerotia formation at the end of the growing season, for the hyphae derived from germinating microsclerotia in the soil, to fungal root attachment and colonisation of the plant host and disease symptom induction.

• DFG Programme: Research Grants