Role of CclA Loss in <i>Parametarhizium changbaiense</i> in Enhancing Priming Resistance of Mung Bean Against Damping Off Induced by <i>Rhizoctonia solani</i>

Rhizoctonia solani is a soil-borne pathogen causing destructive diseases on various economically important crops. Beneficial plant and fungus interactions are well acknowledged to enhance plant resistance to biotic stresses. However, the underlying mechanisms are not fully understood, especially the contribution of fungal epigenetic regulation remains poorly understood. Here, we characterized Parametarhizium changbaiense as a beneficial fungus that promoted mung bean growth and priming resistance to damping off caused by R. solani. Knockout of CclA, a subunit of the COMPASS complex involved in H3K4 methylation, reduced the H3K4me1 and 3 levels in P. changbaiense and diminished the fungal growth and conidiation. However, PcCclA deletion enhanced the root colonisation and further bolstered disease resistance, which correlated with intensified lignin content, lignification in the stem cells, and reactive oxygen species (ROS) scavenging ability, indicating a boost in priming defense responses. Taken together, our findings not only supported a conserved function of PcCclA in fungal growth regulation, but also demonstrated the role of PcCclA-mediated H3K4 methylation in host defense priming, which deepens the understanding of the importance of fungal epigenetic regulation in the plant-beneficial fungus interaction. Meanwhile, we also provided a strategy to enhance priming defense response through epigenetic engineering of plant-beneficial fungi.