Heterotrimeric G-protein signaling in Arabidopsis: Puzzling G-protein-coupled receptor.

Seven transmembrane G-protein-coupled receptors (GPCRs) are commonly used by eukaryotes to sense extracellular signals to switch on cellular responses through the activation of cognate heterotrimeric G-proteins. In Arabidopsis thaliana, GCR2 has been proposed as a GPCR for the plant hormone abscisic acid. On the other hand, biochemical analysis demonstrates that the sole Arabidopsis heterotrimeric G-protein alpha subunit, GPA1, is in the activated state (GTP-bound) by default, suggesting that the heterotrimeric G-proteins may act without any GPCRs.