Subfamily I 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 Ca²⁺ has long been implicated in ethylene signaling, the identity of molecules controlling Ca²⁺ permeability has remained elusive. In this study, we revealed that Arabidopsis subfamily I ethylene receptors ETR1 and ERS1, as well as their homologs across the green lineage, are Ca²⁺ permeable. We found that simultaneous disruption of ETR1 and ERS1 markedly attenuates ethylene-induced elevation in cytosolic Ca²⁺ concentrations in Arabidopsis seedlings, and that both ETR1 and ERS1 exhibit Ca²⁺ permeability in the Xenopus laevis oocyte system and two additional heterologous expression systems. Moreover, we showed that homologs of ETR1 from eight land plants and algal species also exhibit Ca²⁺ permeability, suggesting an evolutionarily conserved function. We further demonstrated that ethylene enhances the Ca²⁺ permeability of ETR1 and its homolog from the charophyte Klebsormidium flaccidum, and a mutation disrupting ethylene binding (Cys65Ser) abolishes the effect of ethylene. These findings uncover a previously unrecognized yet conserved role of ethylene receptors as Ca²⁺-permeable channels in the green lineage, with broad implications for Ca²⁺ signaling in plant development and environmental adaptation.