A helper NLR channels organellar calcium to trigger plant immunity

Abstract

Upon activation, plant NLR immune receptors are known to assemble into oligomeric resistosomes that insert into the plasma membrane, forming Ca2+-permeable channels and triggering immunity. Here, we show that the RPW8-like coiled-coil (CCR-) NLR NRG1 primarily targets organelles instead of the plasma membrane. Unlike canonical CC-NLRs, activated NRG1 accumulates at the chloroplast envelope and channels stromal Ca2+ into the cytosol. AlphaFold modeling of the NRG1 resistosome reveals an unusually long N-terminal membrane-insertion structure that would span the double chloroplast membranes. Nanobody-mediated relocalization shows functional membrane specificity: chloroplast trapping abolishes activity of the canonical helper CC-NLR NRC4 but not NRG1. NRG1 orthologs, from non-flowering lineages to angiosperms, target chloroplasts, suggesting that organelle-centered defense dates back to at least [~]360 million years. We propose that coiled-coil NLR diversification has enabled compartment-specific immune signaling to capture diverse Ca2+ stores.