Hormone-dependent receptor docking controls calcium channel activity in plants

Abstract

The phytohormone auxin is a central coordinator of plant growth and development. Besides its canonical effect on gene transcription1,2, auxin triggers an ultra-rapid calcium ion influx that initiates the root gravitropic response3. The nature of the so-called rapid auxin pathway connecting the AFB1 auxin receptor3,4 and plasma membrane calcium channels remained unknown. Here, we show that auxin induces the direct interaction of the AFB1 receptor with the CNGC14 calcium channel. As the AFB1 receptor is independent of the ubiquitin ligase complex5, the auxin-induced interaction translates into relocalization of the receptor to the plasma membrane. We identify the interaction interface and provide evidence that the docking of the receptor to the channel complex activates Ca2+ influx and triggers growth inhibition. These findings position a calcium channel as an unprecedented component of the AFB1 auxin receptor complex. The ligand-dependent localization shift of a TIR1/AFB family receptor represents a novel paradigm in signal transduction and opens the possibility of unforeseen branches of auxin signaling pathways.