The Fusarium graminearum secreted protein FgARG3 promotes infection by manipulating plant polyamine metabolism

Deoxynivalenol (DON) is a critical virulence factor for Fusarium graminearum infection. Although DON biosynthesis is induced by the host polyamine putrescine (Put) during infection, the mechanisms driving Put accumulation in the plant remain unknown. This study characterized four arginase genes (FgARGs) in F. graminearum. Among them, knockout of FgARG3 significantly attenuated pathogen pathogenicity on wheat. The complementary strain Δfgarg3/FgARG3 restored pathogenicity, but not in the enzymatically inactive FgARG3m. Exogenous Put application in spikes restored pathogenicity of the Δfgarg3 mutant, confirming its role as a pathogenicity factor. Transient overexpression of FgARG3 in wheat increased plant Put accumulation, which led to higher DON levels and greater susceptibility to F. graminearum. These findings establish a model wherein FgARG3 enables F. graminearum to degrade host arginine and elevate putrescine. This metabolic manipulation, in turn, stimulates DON biosynthesis and enhances the pathogen's virulence.