The functional divergence of two ethylene receptor subfamilies that exhibit Ca ²⁺ -permeable channel activity

Ethylene is a gaseous plant hormone crucial for regulating plant growth, development, and stress adaptation, yet the molecular basis underlying ethylene receptor function remains elusive. Here, we show that subfamily I receptors constitute core ethylene-sensing module and function epistatically to subfamily II receptors. Notably, we discover that only subfamily I receptors possess Ca ²⁺ -permeable channel activity, which are indispensable for ethylene-induced cytosolic calcium influx. Overall, this work supports a mechanistic framework in which subfamily I receptors integrate ethylene sensing with Ca ²⁺ influx, providing new insight into how plants translate hormonal cues into downstream signaling events.