The CgrMbp1-CgrSwi6 complex regulates vegetative growth, asexual development, and pathogenicity in the maize...

Colletotrichum graminicola is the main pathogen causing maize anthracnose, leading to substantial agricultural losses. Accurate regulation of the cell cycle is crucial for fungal development and pathogenicity. Mbp1 and Swi6 are key transcription factors that form the Mlu I cell cycle box binding factor (MBF) complex, regulating the G1/S phase transition in the cell cycle. In this study, we characterized two cell cycle proteins, CgrMbp1 and CgrSwi6, in C. graminicola. Both CgrMbp1 and CgrSwi6 harbor a KilA-N domain and exhibit nuclear localization. Deletion of Cgrmbp1 or Cgrswi6 exhibited markedly reduced growth, with colonies displaying irregular, serrated edges. Furthermore, the ΔCgrmbp1 and ΔCgrswi6 mutants exhibited a significant reduction in conidial formation and germination, as well as a complete loss of virulence. Yeast two-hybrid and bimolecular fluorescence complementation assays verified the physical interaction between CgrMbp1 and CgrSwi6 in the nucleus of C. graminicola. Transcriptomic profiling demonstrated significant downregulation of genes associated with carbon metabolism, cell cycle regulation, cell wall degradation, and virulence factors in both ΔCgrmbp1 and ΔCgrswi6 mutants. In summary, our findings establish that the CgrMbp1-CgrSwi6 protein complex serves as a critical regulator of vegetative growth, conidiation, and pathogenicity in C. graminicola.