Ethylene receptors are functionally conserved in calcium permeability across the green lineage

The gaseous hormone ethylene plays a key role in regulating plant growth and stress responses. Although Ca{superscript 2} has long been implicated in ethylene signaling, the identity of molecules controlling Ca{superscript 2} permeability involved has remained elusive. Here we show that Arabidopsis ethylene receptors ETR1 and ERS1 are Ca2+ permeable, and that ETR1 mediates ethylene-induced cytosolic Ca2+ increase and regulates hypocotyl elongation. Homologs of ETR1 from eight land plant and algal species also exhibit Ca{superscript 2} permeability, suggesting an evolutionarily conserved function. We further demonstrate ethylene enhances the Ca2+ permeability of ETR1 and its homologue from the charophyte Klebsormidium flaccidum. These findings uncover a previously unrecognized but conserved role of ethylene receptors in Ca{superscript 2} permeability regulation in the green lineage, with broad implications for Ca{superscript 2} signaling in plant development and environmental adaptation.