MoCul4 assists MoKmt1 to catalyze H3K9 methylation and regulates the growth, development, and pathogenicity in <i>Magnaporthe oryzae</i>

Notably, the Δ<i>Mocul4</i> mutant displayed similar but more severe developmental defects than Δ<i>Mokmt1</i>, including a 32.8% reduction in growth rate, 90.4% decrease in conidiation, and a significant reduction in lesion area. Both MoCul4 and MoKmt1 were localized in the nucleus. Like Δ<i>Mokmt1</i>, H3K9me3 levels in Δ<i>Mocul4</i> were nearly abolished, suggesting that MoCul4 modulates the methyltransferase activity of MoKmt1.

RNA-seq analysis further revealed that 1,033 out of 2,910 differentially expressed genes (35.5%) were co-regulated by both MoKmt1 and MoCul4. The expression level of <i>MoMAT1-1</i> and <i>MoMAT A1-1</i>, located in heterochromatin, was upregulated in both mutants, indicating compromised integrity of heterochromatin. This study demonstrates that MoCul4, functioning in the same pathway as MoKmt1 in <i>M. oryzae</i>, orchestrates the MoKmt1-mediated H3K9me3 epigenetic regulatory network, thereby providing a theoretical foundation for developing novel fungicides targeting epigenetic regulation.</p>