The RING-type E3 ubiquitin ligase CgrUbr1 regulates vegetative growth, hyphal morphology, asexual development, and pathogenicity in Colletotrichum graminicola

Abstract Colletotrichum graminicola is a significant phytopathogenic fungus responsible for maize anthracnose. Ubr1 functions as a critical RING-type E3 ubiquitin ligase within the N-degron pathway; however, its specific role in Colletotrichum species remains poorly understood. In this study, we characterized the Ubr1 homolog, CgrUbr1, in C. graminicola . Bioinformatics analysis revealed that CgrUbr1 possesses the canonical zf-UBR, ClpS, and RING domains. Disruption of Cgrubr1 resulted in a significantly reduced growth rate, distinct segmental swelling, a characteristic bead-like hyphal morphology, and a higher frequency of septation. Regarding asexual development, the Δ Cgrubr1 mutants exhibited a severe reduction in the yield of both oval and falcate conidia, both of which displayed pronounced morphological defects. Furthermore, oval conidia exhibited negligible germination rates, while falcate conidia were unable to differentiate into typical appressoria. Pathogenicity assays confirmed that Cgrubr1 deletion drastically attenuated virulence on maize leaves, failing to produce visible lesions on intact tissue. Transcriptomic profiling revealed significant dysregulation of genes involved in DNA replication, chitin metabolism, and infection-related pathways in the mutant strain. Collectively, these findings demonstrate that CgrUbr1 is indispensable for vegetative growth, hyphal morphogenesis, asexual reproduction, and pathogenicity in C. graminicola .