Poster # 312

Youhuang Xiang¹, Reynaldi Darma², Martin Darino², Namrata Jaiswal³, Matthew Helm³, Kim E. Hammond-Kosack², and Roger W. Innes¹
1. Indiana University, Department of Biology, Bloomington, IN 47405, U.S.
2. Protecting Crops and the Environment, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, U.K.
3. Crop Production and Pest Control Research Unit, U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS), West Lafayette, IN 47907, U.S.
Corresponding Author: Roger W. Innes, rinnes@iu.edu

Xiang, Youhuang

youxiang@iu.edu

Chloroplasts are a prime target of phytopathogen effectors due to their contributions to plant immune responses. However, the virulence mechanisms of chloroplast-targeted effectors remain poorly understood. In this study, we systematically characterized a conserved protease-like effector candidate (FgTPP1) from the fungal pathogen Fusarium graminearum. FgTPP1 contains a chloroplast targeting sequence and accumulates inside chloroplasts. Surprisingly, accumulation inside chloroplasts attenuates the ability of FgTPP1 to suppress immune responses, including chitin-mediated activation of MAP kinase signaling, chloroplast-derived reactive oxygen species (ROS) production, cell death triggered by the NLR protein RPS5 and Pseudomonas-induced hypersensitive response in wheat. These observations indicate that the activity of FgTPP1 is both temporally and spatially regulated. Interestingly, FgTPP1 localized to the cytoplasm forms mobile punctate condensates via phase separation and sequesters the wheat chloroplast protein PetC in cytoplasmic condensates by direct interaction. We therefore hypothesize that FgTPP1 functions in the cytoplasm during early infection stages to suppress immune responses, and is subsequently inactivated by chloroplast import, enabling cell death and transition to a necrotrophic phase. These findings reveal a previously unknown effector mechanism for regulating immune responses using spatiotemporal dynamics.

© Copyright 2025 by individual authors. All rights reserved. No part of this abstract or paper publication may be reproduced without prior permission from the applicable author(s).