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Concurrent Session

Session: Concurrent Session: Extracellular & Intracellular non-self recognition & signaling (1)

Enzymatic and Ion Channel Activities of Plant Intracellular Immune Receptors

Monday, July 14, 2025
15:35 - 15:55  
Location: Room M+N

Plant intracellular NLR immune receptors with an N-terminal TIR domain sense pathogen effectors to initiate immune signaling. Lipase-like proteins, EDS1, SAG101, and PAD4, transduce immune signals from sensor TIR-NLRs to helper CCR-NLRs including NRG1 and ADR1. We report the structure and function of Arabidopsis EDS1-PAD4-ADR1 heterotrimer in complex with pRib-AMP/ADP activated by plant TIR or bacterial TIR producing 2’cADPR. 2’cADPR can be hydrolyzed into pRib-AMP and thus activates EDS1-PAD4-ADR1 defense signaling. We demonstrate that the Arabidopsis EDS1-SAG101-NRG1A heterotrimer formation is stabilized by the NRG1A loss-of-oligomerization mutant L134E. We report structures of ADPr-ATP-bound EDS1-SAG101-NRG1A L134E and EDS1-SAG101-NRG1C heterotrimers with similar assembly mechanisms. The truncated NRG1C maintains core interacting domains of NRG1A but develops further interactions with EDS1-SAG101 to outcompete NRG1A and suppress cell death function. Hepler NLRs including NRG1A rely on positive charged residues in the N-terminal CCR domain for phospholipid binding and plasma membrane association. NRG1C lacks CCR domain and shows nucleocytoplasmic localization, facilitating its sequestration of nucleocytoplasmic EDS1-SAG101. Effector activation of TIR-NLR leads to oligomerization and puncta formation of NRG1 at plasma membrane. Auto-active NRG1 and ADR1 function as cation channels at plasma membrane. Our study unveils mechanisms underlying cross-activation between plant and bacterial immunity and key signaling events of how TIR-NLR enzymatic activity activates CCR-NLR channel activity.