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Calcium serves as a second messenger in a variety of developmental and physiological processes and has long been identified as important for plant immune responses. We discuss recent discoveries regarding plant immune‐related calcium‐permeable channels and how the two intertwined branches of the plant immune system are intricately linked to one another through calcium signalling. Cell surface immune receptors carefully tap the immense calcium gradient that exists between apoplast and cytoplasm in a short burst via tightly regulated plasma membrane (PM)‐resident cation channels. Intracellular immune receptors form atypical calcium‐permeable cation channels at the PM and mediate a prolonged calcium influx, overcoming the deleterious influence of pathogen effectors and enhancing plant immune responses.
Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. In
Arabidopsis, a subfamily of “helper” NLRs is required by many “sensor” NLRs. Active NRG1.1 oligomerized, was enriched in plasma membrane puncta, and conferred cytoplasmic calcium ion (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 affecting 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 demonstrated that Arabidopsishelper NLRs form Ca2+-permeable cation channels to directly regulate cytoplasmic Ca2+levels and consequent cell death. Thus, helper NLRs transduce cell death signals directly.