Maize diterpenoid sensing via Ste3 a-pheromone receptor and rapid germination of Colletotrichum graminicola oval conidia facilitating root infection

Most plant pathogenic microorganisms have evolved to infect distinct host tissues. The maize anthracnose fungus Colletotrichum graminicola is known for its ability to invade above-ground tissues with asexual falcate conidia. In addition, C. graminicola produces a second asexual spore type, oval conidia. This study investigates the specific adaptations that make oval conidia suitable for maize root infection, demonstrating that only oval conidia exhibit root pathogen characteristics. These include the ability to germinate in soil and grow chemotropically toward root-secreted molecules. High-performance liquid chromatography/mass spectrometry (HPLC/MS) analyses combined with biological assays indicate that diterpenoids, such as dihydrotanshinone I, are likely responsible for the chemical attraction of C. graminicola. Genetic analysis identified the a-pheromone receptor CgSte3 as responsible for diterpenoid perception by the fungal pathogen. In conclusion, the understanding of maize anthracnose disease must be expanded to include an elaborate root infection cycle by oval conidia.