Specific communication processes of distinct conidia types during germination, early colony development, and host plant infection of the fungal maize pathogen Colletotrichum graminicola

• Applicant: Dr. Daniela Elisabeth Nordzieke
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms ; General Genetics and Functional Genome Biology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447175909

Within the last two decades, reports on outbreaks of plant infections caused by filamentous fungi increased, including important crop plants like corn, wheat, rice, and potato. Colletotrichum graminicola is the causal agent of corn anthracnose, a disease with the annual economic potential of about 1 billion US dollars only in the USA. During infection, two specific infectious fungal spore types regulate central pathogenicity processes. Falcate-shaped conidia formed on infected leaves secrete mycosporine derivatives into the surrounding mucilage. These signaling molecules inhibit the germination of this spore type in dependence of nutrients and spore density. Oval conidia, on the other hand, generate signals allowing the coordinated fusion of young germlings. Intriguingly, both spore-specific signals fundamentally influence the infection strategy of this maize pathogen. Since both secreted signals are absent from the other spore type, we will seek to unravel external stimuli, biosynthesis, and detailed functions of these spore-specific signals of C. graminicola. Mycosporines are secondary metabolites involved in protection from UV-radiation alike as oxidative and osmotic stress. In our pre-experiments we have found that homologous genes of the mycosporine biosynthesis in cyanobacteria are expressed in a tissue-dependent way in C. graminicola. Using in silico analyses, we were further able to identify a putative secondary metabolite cluster for the generation of mycosporines in this fungus. In an approach combining functional studies of specific mycosporine derivatives, we will seek to identify the biosynthesis pathways of mycosporines in C. graminicola applying RNAseq, genetic, and phenotypic analyses of deletion mutants. Based on these findings we aim to unravel the role of these secondary metabolites in spore-specific life-cycle and pathogenicity of this plant pathogen. Formation of vegetative cell fusions is a highly conserved process in filamentous ascomycetes. It is anticipated that this process increases the fitness of a fungal colony by optimizing nutrient availability and coordinating developmental processes and growth patterns. During the fusion formation, a cellular dialog of the future fusion partners takes place: both partners secrete a yet unknown signal in an alternate fashion, guiding the corresponding partners towards each other. To facilitate the identification of the fusion signal, we established a pipeline including methods for signal generation, isolation, and evaluation. Based on this pipeline we will apply analytical methods comparing the secretomes generated by oval and falcate conidia to identify the corresponding signal by HPLC/MS analyses. Further, we will verify the obtained results using genetic and phenotypical analyses of deletion mutants. This will additionally allow determining the impact of the fusion signal as a probable virulence factor of C. graminicola.

• DFG Programme: Research Grants