Ethylene receptors at the ER: Potential hubs integrating hormone, redox, and Ca2+ signaling.

Arabidopsis thaliana Ethylene Response 1 (ETR1) has long been viewed as a canonical hormone receptor initiating ethylene signaling at the endoplasmic reticulum (ER). Recent studies demonstrate that ETR1 also acts as an ER redox sensor, with disulfide-dependent dimerization controlling receptor conformation and activity. In parallel, subfamily I ethylene receptors, including ETR1, function as Ca2+-permeable channels, directly linking ethylene perception to rapid cytosolic Ca2+ elevation. Here, we summarize emerging evidence that redefines ETR1 as a multifunctional signaling hub connecting ethylene perception, redox regulation, and Ca2+ signaling. We present this integration as a working model and highlight unresolved questions concerning the mechanistic relationships among these functions. This framework provides a new perspective on how plants integrate ER homeostasis with hormone signaling to coordinate development and stress adaptation.