FgNdk1 Promotes Effector Secretion to Scavenge ROS During Fusarium graminearum Infection.

Pathogens secrete numerous effectors to overcome plant-derived reactive oxygen species (ROS), but how pathogens modulate effector secretion during infection remains unclear. In this study, we showed that the nucleotide diphosphate kinase Ndk1 in Fusarium graminearum plays important roles in vegetative growth, conidiation, sexual reproduction and pathogenicity. The species-specific N-terminus and three active sites of FgNdk1 functioned in the development and virulence of F. graminearum and contributed to its enzymatic activity. Protein structure results showed that the N-terminus is rich in proline, and subcellular localisation and enzymatic activity assays confirmed that it was responsible for endoplasmic reticulum (ER)-anchoring; additionally, the proline-rich feature contributed to the role of the N-terminus in enzymatic activity. We further revealed that the N-terminus of FgNdk1 exhibited a loosened structural conformation, likely facilitating the activity of FgNdk1 anchored in the ER. Moreover, FgNdk1 significantly suppressed ROS in planta. Comparative transcription analysis showed that 16 effector genes were differentially expressed in the Fgndk1 mutant, particularly during the infection stage. FgNdk1 greatly promoted the secretion of effectors FgSp10, FgSp16 and FgSp24 FgSP, which were important for the virulence of F. graminearum and ROS detoxification. Overall, FgNdk1 contributes to virulence by promoting effector secretion to scavenge ROS in planta, and its proline-rich species-specific N-terminus enhances enzymatic activity, further influencing the development and virulence of F. graminearum. These findings elucidate the mechanism by which effector secretion is modulated by an ER-anchored protein during plant fungal pathogen invasion.