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 Ca 2+ has long been implicated in ethylene signaling, the identity of molecules controlling Ca 2+ permeability has remained elusive. Here we show that Arabidopsis subfamily I ethylene receptors ETR1 and ERS1, as well as their homologs across the green lineage, are Ca 2+ permeable. We found that simultaneous disruption of ETR1 and ERS1 markedly attenuates ethylene-induced elevation in cytosolic Ca 2+ concentrations in Arabidopsis seedlings, and that both proteins exhibit Ca 2+ permeability in the Xenopus laevis oocyte system and two additional heterologous expression systems. Moreover, we showed that homologs of ETR1 from eight land plant and algal species also exhibit Ca 2+ permeability, suggesting an evolutionarily conserved function. We further demonstrate ethylene enhances the Ca 2+ permeability of ETR1 and its homologue from the charophyte Klebsormidium flaccidum , and a mutation to disrupt ethylene binding (Cys65Ser) abolishes the ethylene influence. These findings uncover a previously unrecognized yet conserved role of ethylene receptors as Ca 2+ -permeable channels in the green lineage, with broad implications for Ca 2+ signaling in plant development and environmental adaptation.