New Phytologist Now: Stomata

Heterotrimeric G protein regulation of guard cell signalingHeterotrimeric G proteins, composed of Gα, Gβ, and Gγ subunits, are intracellular signaling proteins known to regulate stomatal apertures in response to signals such as ABA and VPD (Wang et al., 2001, Zait et al., 2024). Elevated intercellular CO2 concentrations also engender stomatal closure. However, potential G protein involvement in CO2 sensing has not been investigated, despite substantial recent process in uncovering the signaling network underlying the guard cell CO2 response (Takahashi et al., 2022, Gan et al., 2024). We determined via gas exchange and stomatal aperture measurements that Arabidopsis T-DNA knockouts in the canonical GTP-binding Gα subunit gene, GPA1, are impaired in CO2-induced stomatal closure. Unexpectedly, point mutants of GPA1 that fail to bind or hydrolyze GTP restore CO2-induced stomatal closure in gpa1 null lines. This result implicates other features of GPA1, rather than the classic G protein cycle, in CO2-stimulated signal transduction. We assayed known protein components of the CO2 network for interaction with GPA1 and identified several positive interactors, including the K+ efflux channel, GORK. Our electrophysiological assays in Xenopus oocytes implicate direct ion channel regulation by GPA1 as a key mechanism controlling stomatal apertures in the CO2 response.