Acyl-CoA Oxidase-Mediated β-Oxidation Regulates the Lifestyle Transition of Metarhizium rileyi from Insect Pathogen to Plant Mutualist.

Metarhizium rileyi as a widely distributed insect pathogenic fungus, has a promising application prospect in pest control. This study investigates M. rileyi strain XSBN200920 following its endophytic colonization of Nicotiana benthamiana. The fungus establishes systemic endophytic relationships via foliar spray and root drench, significantly improving plant height, stem thickness, leaf area, biomass, and chlorophyll content. Colonized plants showed more than 50% reduction in Spodoptera litura damage and approximately 70% decrease in Alternaria alternata disease severity. Multiomics analyses revealed systemic metabolic reprogramming with activated jasmonic acid and salicylic acid pathways. The fungal acyl-CoA oxidase gene MrACOX1, essential for peroxisomal β-oxidation, was highly expressed during colonization. ΔMrACOX1 deletion eliminated growth promotion, induced systemic resistance, and caused abnormal conidia with thicker cell walls. Metabolomics showed MrACOX1 regulates lipid homeostasis and organic acid metabolism, affecting colonization fitness. This study has provided molecular targets for the development of multifunctional microbial inoculants.