The Role of Gβ Protein in Controlling Cell Expansion via Potential Interaction with Lipid Metabolic Pathways

Heterotrimeric G-proteins influence almost all aspects of plant growth, development, and responses to biotic and abiotic stresses in plants, likely via their interaction with specific effectors. However, the identity of such effectors and their mechanism of action are mostly unknown. While investigating the roles of different G-protein subunits in modulating the oil content in Camelina (Camelina sativa), an oil seed crop, we uncovered a role of Gβ proteins in controlling anisotropic cell expansion. Knockdown of Gβ genes causes reduced longitudinal and enhanced transverse expansion, resulting in altered cell, tissue, and organ shapes in transgenic plants during vegetative and reproductive development. These plants also exhibited substantial changes in their fatty acid and phospholipid profiles, which possibly leads to the increased oil content of the transgenic seeds. This increase is potentially caused by the direct interaction of Gβ proteins with a specific patatin-like phospholipase, pPLAIIIδ. Camelina plants with suppressed Gβ expression exhibit higher lipase activity, and show phenotypes similar to plants overexpressing pPLAIIIδ, suggesting that the Gβ proteins are negative regulators of pPLAIIIδ. These results reveal interactions between the G-protein-mediated and lipid signaling/metabolic pathways, where specific phospholipases may act as effectors that control key developmental and environmental responses of plants.