The Arabidopsis heterotrimeric G protein α subunit binds to and inhibits the inward rectifying potassium channel KAT1

In animal cells, Gα subunit of the heterotrimeric G proteins can bind to both the N-terminal and C-terminal domains of G-protein-activated inwardly rectifying K⁺ channels (GIRKs) to inhibit their activities. In Arabidopsis guard cells, the Gα subunit GPA1 mediates multiple stimuli-regulated stomatal movements via inhibiting guard cell inward-rectifying K⁺ (K⁺_in) current, but it remains unclear whether GPA1 directly interacts with and inhibits the activities of K⁺_in channels. Here, we found that GPA1 interacted with the transmembrane domain rather than the intracellular domain of the Shaker family K⁺_in channel KAT1. Two-Electrode Voltage-Clamp experiments in Xenopus oocytes demonstrated that GPA1 significantly inhibited KAT1 channel activity. However, GPA1 could not inhibit the assembly of KAT1 as well as KAT2 as homo- and hetero-tetramers and alter the subcellular localization and protein stability of these channels. In conclusion, these findings reveal a novel regulatory mechanism for Gα inhibition of the Shaker family K⁺_in channel KAT1 via binding to its channel transmembrane domains but without affecting its subcellular localization, protein stability and the formation of functional homo- and hetero-tetramers. This suggests that in both animal and plant cells, Gα can regulate K⁺_in channels through physical interaction, albeit with differing mechanisms of interaction and regulation.