Plant "helper" immune receptors are Ca 2+ -permeable nonselective cation channels.

Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. In Arabidopsis , a subfamily of "helper" NLRs are required by many "sensor" NLRs. Active NRG1.1 oligomerized, was enriched in plasma membrane puncta and conferred cytoplasmic Ca2+ influx in plant and human cells. NRG1.1-dependent Ca2+ influx and cell death were sensitive to Ca2+ channel blockers and were suppressed by mutations impacting oligomerization or plasma membrane enrichment. Ca2+ influx and cell death mediated by NRG1.1 and ACTIVATED DISEASE RESISTANCE 1 (ADR1), another "helper" NLR, required conserved negatively charged N-terminal residues. Whole-cell voltage-clamp recordings demonstrate that Arabidopsis "helper" NLRs form Ca2+ -permeable cation channels to directly regulate cytoplasmic Ca2+ levels and consequent cell death. Thus, "helper" NLRs transduce cell death signals directly.