AbstractsHeterotrimeric G protein-mediated signaling plays a vital role in physiological and developmental processes in eukaryotes. On the other hand, because of the absence of a G protein-coupled receptor and self-activating mechanism of the Gα subunit, plants appear to have different regulatory mechanisms, which remain to be elucidated, compared to canonical G protein signaling established in animals. Here we report thatArabidopsisheterotrimeric G protein subunits, such as Gα (GPA1) and Gβ (AGB1), regulate plant growth under stress conditions through the analysis of heterotrimeric G protein mutants. Flg22-mediated growth inhibition in wild-type roots was found to be caused by a defect in the elongation zone, which was partially blocked inagb1-2but notgpa1-4. These results suggest thatAGB1may negatively regulate plant growth under biotic stress conditions. In addition,GPA1andAGB1exhibited genetically opposite effects onFCA-mediated growth inhibition under heat stress conditions. Therefore, these results suggest that plant G protein signaling is probably related to stress-mediated growth regulation for developmental plasticity in response to biotic and abiotic stress conditions.