GcPG and GcGel: Verification of Their Key Roles in Geotrichum citri-aurantii Infecting Citrus via Overexpression and Effects on Fruit Membrane Lipid.

The pathogen Geotrichum citri-aurantii causes postharvest sour rot disease in citrus fruit worldwide, severely impacting the commercial development and economic value of citrus. However, research on G. citri-aurantii commenced relatively late, and the pathogenic mechanisms are incompletely understood. This study successfully constructed OE-GcPG2# and OE-GcGel5# overexpressing lines via PEG-mediated protoplast transformation. Compared to WT, the overexpressing strains enhanced pathogenicity by increasing chitin levels through the elevated expression of GcPG, GcGel, GcAGA, and GcCs. They promoted degradation of citrus protopectin, enhanced expression of key membrane lipid metabolism genes CitPLD and CitLOX, and increased malondialdehyde (MDA) accumulation, thereby compromising cell membrane integrity. This demonstrated that GcPG and GcGel represent critical targets for driving the progression of sour rot, filling gaps in our understanding of the pathogenic mechanisms of G. citri-aurantii. These findings hold significant implications for future drug target development and the advancement of integrated management strategies against sour rot.