P-160 - The F. graminearum effector TPP1 hijacks the chloroplast iron-sulfur protein and dynamically regulates plant defense via phase separation

Chloroplasts are a prime target of pathogen effectors to suppress host immune responses. However, the molecular mechanisms by which chloroplast-targeted effectors impact chloroplast function remain largely unclear. Here we show that the TPP1 protease from the fungal pathogen Fusarium graminearum targets the wheat chloroplast protein PetC. Association with PetC sequesters PetC in condensates in the cytoplasm, preventing its import into chloroplasts. Surprisingly, TPP1 can self-process into a form that is rapidly imported into chloroplasts where it is cleaved by stromal processing peptidases, likely inactivating it. Translocation of TPP1 weakens its role in suppression of cell death induced by the NLR protein RPS5, suggesting that TPP1 can dynamically manipulate plant immune responses by interfering with both effector-triggered immunity (ETI) and PAMP-triggered immunity (PTI). We therefore hypothesize that TPP1 functions early during infection to suppress chloroplast-derived ROS to facilitate Fg invasion, and subsequently is turned off by chloroplast import, enabling cell death and transition to a neurotrophic phase. These findings reveal a previously unknown effector interference mechanism that effector exerts dual action in disrupting chloroplast function to regulate host immunity.