Protease-Mediated Dual Action Against Rice Blast: Suppression of Magnaporthe oryzae Ergosterol Biosynthesis Pathway and Enhancement of Rice Disease Resistance by Bacillus amyloliquefaciens SN16-1.

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, poses a severe threat to global rice production. While biological control represents a promising sustainable strategy, the molecular mechanisms by which biocontrol agents suppress M. oryzae remain poorly understood. Our findings elucidate a novel mechanism of bacterial biocontrol, wherein a secreted bacterial protease modulates fungal signalling pathways to disrupt its environmental fitness and pathogenic structures, while enhancing host resistance to blast disease. We demonstrate that the Bacillus amyloliquefaciens SN16-1 exhibits antagonistic activity against M. oryzae Guy11. Integrated dual RNA sequencing and protein-protein interaction analysis revealed that the ergosterol biosynthesis pathway in M. oryzae is crucial for its pathogenicity and is markedly suppressed during co-culture with SN16-1. We identified MoERG1, a key enzyme in this pathway, as essential for fungal development and virulence. Further analysis showed that the serine protease AprE, secreted by SN16-1, is a critical mediator. AprE triggers the Hog1-MAPK signalling cascade in M. oryzae, leading to transcriptional repression of ergosterol biosynthesis genes, concomitant activation of plant disease resistance, and induction of ROS accumulation, hyperosmotic stress and apoptosis in fungal hyphae. This study provides new insights into host-microbe-pathogen interactions and offers an effective strategy for developing targeted biocontrol solutions against devastating plant diseases.