image: Upon perception of blast pathogen effectors by the NLR, PIBP4 and OsRab5a-mediated trafficking vesicles likely promote the localization of part of PigmR to microdomains where PigmR interacts with and activates OsRac1, which triggers ROS signaling and leads to disease resistance.
Credit: ©Science China Press
This study is led by Professor Zuhua He's research team from Center for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences, in collaboration with the team led by Junzhong Liu from Yunnan University.
Rice production is critical to food security worldwide. However, the rice blast fungus Magnaporthe oryzae (M. oryzae) causes destructive disease and huge yield loss worldwide. Exploiting and breeding rice with broad-spectrum resistance to rice blast is therefore of great value for ensuring global food production. The research group, led by Professor He Zuhua, identified the broad-spectrum blast resistance gene Pigm (Science, 2017), reported that RRM transcription factors interact with the immune protein PigmR and regulated broad-spectrum blast resistance in rice (Molecular Cell, 2019), and discovered for the first time that PigmR governs an arms race with the fungal virulent effector proteins with a competitive mode that hinges on a critical metabolic pathway of defense molecule production (Nature, 2021).
To further identify the components of PigmR-mediated immune signaling, this study performed a yeast two-hybrid screen and found that PIBP4 (PigmR Interacting and Blast resistance Protein 4), a predicted PRENYLATED RAB ACCEPTOR domain (PRA) protein, interacted with full-length PigmR in yeast. The interactions between PIBP4 and PigmR were confirmed through an immunoprecipitation assay, an in vitro pull-down assay, bimolecular fluorescence complementation (BiFC) assays, and split luciferase complementation assays in tobacco. Pathogen inoculation and disease resistance assays revealed that knockout of PIBP4 significantly decreased PigmR-mediated blast resistance, suggesting that PIBP4 was required for full PigmR-mediated blast resistance.
This study further identified the small GTPase OsRab5a as an interacting partner of PIBP4. OsRab5a also interacted with PigmR and modulated PigmR-mediated blast resistance. The absence of PIBP4 and OsRab5a compromised the microdomain localization of PigmR, as revealed by immunofluorescence analysis, total internal reflection fluorescence microscopy (TIRFM), and liquid chromatography-mass spectrometry (LC-MS)/MS analysis, suggesting that PIBP4 and OsRab5a are required for partitioning or transportation of PigmR to microdomains. This study discovered that PigmR protein in microdomains interacted with and activated OsRac1, leading to the generation of reactive oxygen species (ROS) bursts in rice. This research discovers a previously unknown mechanism that deploys a PRA-Rab protein-delivering hub to ensure ETI, linking the membrane trafficking machinery with NLR function and immune activation in plants.
Journal
Science Bulletin