The Methyltransferase Cc <scp>Kmt3</scp> Regulates Cell Wall Degradation Enzymes Activity to Enhance the Infection Process in <i>Cytospora chrysosperma</i>

Woody canker diseases cause devastating timber losses worldwide. Canker fungi exploit cell wall-degrading enzymes (CWDEs) to promote plant infection, yet the underlying mechanism of the transcriptional regulation of CWDEs remains largely unknown. Using RNA-seq analysis and biochemical assays, we show that the poplar pathogen Cytospora chrysosperma upregulates CWDEs during canker progression, especially increased secretion of laccases. The histone lysine methyltransferase Kmt3 (CcKmt3) is induced by C. chrysosperma infection. Loss of CcKmt3 leads to a genome-wide reduction in H3K36me3 methylation. The ΔCckmt3 strain presented hyphal growth defects, reduced production of hydrolytic enzymes, and impaired virulence. By combining ChIP-seq with RNA-seq, we demonstrated that CcKmt3 controls two hydrolases, CcLac11 and CcPme5, for plant cell degradation and virulence in C. chrysosperma. Furthermore, we showed that CcKmt3 affects hyphal growth by regulating the fungal cell wall integrity pathway. Taken together, this study demonstrates that CcKmt3 regulates the transcriptional expression of genes related to CWDEs by modulating H3K36me3 levels. This regulation influences enzyme activity, ultimately impacting the degradation of the plant cell wall and the pathogenicity processes of the poplar canker fungus.