Recognition-dependent activation of the Arabidopsis RRS1-R/RPS4 TIR-NLR immune receptor pair.

RPS4 and RRS1 in Arabidopsis thaliana acquire NADase activity upon recognition of cognate effectors, while their oligomer size remains unchanged with effector provision.

• Why it matters: NADase activation by plant TIR proteins is linked to defense signaling, but how effector recognition activates the RPS4/RRS1 receptor pair is unclear.
• What they did: The study tested effector-dependent NADase activity and measured RPS4/RRS1 oligomerization, finding that defense activation requires RPS4 catalytic glutamate and its BB-loop motif.
• The result: Effector-dependent immune activation depends on RPS4’s catalytic features, whereas oligomerization occurs without enzymatic activity, implying effector-driven conformational reconfiguration within the oligomer.