The peroxisome RING-type E3 ubiquitin ligase-mediated peroxisome function is essential for Alternaria alternata pathogenicity: coordinated regulation of lipid metabolism homeostasis and redox balance.

Peroxisomes, as single-membrane-bound organelles in eukaryotes, are essential for the growth and development of filamentous fungi. The peroxisome RING-type E3 ubiquitin ligases PEX2, PEX10, and PEX12 are crucial for peroxisome biogenesis. In this study, targeted gene knockout technology was employed to investigate the biological functions of AaPex2, AaPex10, and AaPex12 in Alternaria alternata. Phenotypic analysis demonstrated that the deletion of AaPex2, AaPex10, and AaPex12 significantly inhibited growth, sporulation, and infection structure formation. Transmission electron microscopy (TEM) and qRT-PCR analyses indicated that the absence of these genes disrupted peroxisome structure and impaired the metabolic functions of the organelles. Further investigations revealed that fatty acid utilization was impaired in ΔAaPex2, ΔAaPex10, and ΔAaPex12 mutants, leading to the accumulation of lipid droplets. Additionally, these mutants exhibited reduced hydrogen peroxide levels, impaired superoxide anion scavenging capacity, and dysregulation of reactive oxygen species (ROS) related genes. Disruptions in lipid metabolism and redox homeostasis resulted in elevated malondialdehyde levels, enhanced membrane permeability, and downregulation of ergosterol synthesis genes, ultimately compromising cell membrane integrity. Furthermore, the pathogenicity of all three mutant strains was significantly reduced. This study elucidates the mechanisms by which AaPex2, AaPex10, and AaPex12 influence fungal development and pathogenicity through the modulation of peroxisome structure and metabolic functions in A. alternata. These findings provide a theoretical foundation for developing novel control strategies against postharvest pear black spot disease by targeting peroxisomes.