Hyphal Fusions Enable Efficient Nutrient Distribution in Colletotrichum graminicola Conidiation and Symptom Development on Maize

Abstract

Hyphal and germling fusion is a common phenomenon in ascomycetous fungi. Due to the formed hyphal network, this process enables a coordinated development as well as an interaction with plant hosts and efficient nutrient distribution. Recently, our laboratory work demonstrated a positive correlation between germling fusion and the formation of penetrating hyphopodia on maize leaves outgoing from Colletotrichum graminicola oval conidia. To investigate the probable interconnectivity of these processes, we generated a deletion mutant in Cgso, in which homologs are essential for cellular fusion in other fungal species. However, hyphopodia development was not affected, indicating that both processes are not directly connected. Instead, we were able to link the cellular fusion defect in ∆Cgso to a decreased formation of asexual fruiting bodies of C. graminicola on the leaves. The monitoring of a fluorescent-labelled autophagy marker, eGFP-CgAtg8, revealed a high autophagy activity in the hyphae surrounding the acervuli. These results support the hypothesis that the efficient nutrient transport of degraded cellular material by hyphal fusions enables proper acervuli maturation and, therefore, symptom development on the leaves.

Long-distance gene flow and recombination shape the evolutionary history of a maize pathogen

“…Sexual reproduction has been observed under laboratory conditions, suggesting an absence of prezygotic reproductive barriers between genetically divergent strains (Rogério et al, 2023), as observed in other plant pathogenic ascomycetes (Le Gac and Giraud 2008). Although the sexual state of this species has not been documented in nature, our data suggest a significant contribution of genetic recombination, resulting from either sexual recombination or other nonmeiotic recombination mechanisms, such as parasexual events via hyphal anastomosis, as previously described in other Colletotrichum species (Roca et al 2003;Rosada et al 2010;Souza-Paccola et al 2003;Vaillancourt et al 2000;Nordzieke 2022).…”

Maize diterpenoid sensing via Ste3 a-pheromone receptor and rapid germination ofColletotrichum graminicolaoval conidia facilitating root infection

“…Therefore, oval conidia contain a variable number of nuclei and secondary metabolites promoting dormancy are absent. Those differences cumulate in distinct leaf infection strategies for both conidia types as we reported previously 29,30 . Together, these findings imply so far unexplored but specific roles of both spore types in the maize anthracnose cycle.…”

“…After transformation, regenerating protoplasts were selected on medium containing hygromycin B (500 µg/ ml, transformation of pCgste3_KO) or nourseothricin-dihydrogen sulphate (70 µg/ ml, transformation of pCgste3_nat). To obtain homokaryotic strains, single spore isolations were performed of antibiotic-resistant and PCR-verified primary transformants (Nordzieke, 2022).…”

“…These differences influence the morphological and physiological properties of both spore types. Falcate conidia are single-nucleate and dormant due to the production of mycosporines, while oval conidia contain variable nuclei and lack secondary metabolites promoting dormancy, leading to distinct infection strategies (Panaccione et al, 1989, Nordzieke et al, 2019b, Nordzieke, 2022. These findings suggest unexplored but specific roles of both spore types in the maize anthracnose cycle.…”

“…The 5' and 3' regions of Cgste3 were amplified together with the Cgste3 gene in a PCR using genomic DNA of C. graminicola as template (Ste3_c_fw//Ste3_c_rv; 3,215 bp). As backbone for the assembly reaction served pJet_nat linearized with EcoRV(Nordzieke, 2022), resulting in a resistance to nourseothricin-dihydrogen sulphate in C. graminicola strains transformed with this plasmid.…”