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Poster

Session: Session 1 Presenting Authors at Posters (Odds)

P-021 - Cryo-EM structure of the extracellular region of CARD1/HPCA1

Monday, July 14, 2025
13:30 - 15:15  
Location: Confex Hall 3
Extracellular & Intracellular non-self recognition & signaling
Reactive oxygen species (ROS) are important signaling molecules that regulate plant immune responses. We have previously identified CARD1/HPCA1 gene, which is required for both quinone and hydrogen peroxide (H2O2) responses in plants. CARD1 encodes a leucine-rich repeat (LRR) receptor-like kinase with conserved six cysteine residues at the C-terminal end of its extracellular region forming a unique cysteine region. Here, we purified the extracellular region of Arabidopsis CARD1 (EctoCARD1) expressed in the apoplastic space of Nicotiana benthamiana and determined its three-dimensional structure using cryo-EM. The solved EctoCARD1 structure showed that all six cysteine residues in the unique cysteine region are oxidized and form three intramolecular disulfide bonds. We validated these disulfide bond in vivo through a cysteine labeling assay. Additionally, we have identified a conserved histidine triad on the surface of the CARD1 LRR domain that coordinates a copper ion and is required for elevation of cytosolic [Ca2+] in response to H2O2. We will discuss the possible mechanisms of CARD1-dependent perception of ROS signaling.