Regulatory interaction of the Gα protein with phospholipase A 2 in the plasma membrane of Eschscholzia californica

Abstract

Plant heterotrimeric G-proteins are involved in a variety of signaling pathways, though only one α and a few βγ isoforms of their subunits exist. In isolated plasma membranes of California poppy (Eschscholzia californica), the plant-specific Gα subunit was isolated and identified immunologically and by homology of the cloned gene with that of several plants. In the same membrane, phospholipase A2 (PLA2) was activated by yeast elicitor only if GTPγS (an activator of Gα) was present. From the cholate-solubilized membrane proteins, PLA2 was co-precipitated together with Gα by a polyclonal antiserum raised against the recombinant Gα. In this immunoprecipitate and in the plasma membrane (but not in the Gα-free supernatant) PLA2 was stimulated by GTPγS. Plasma membranes and immunoprecipitates obtained from antisense transformants with a low Gα content allowed no such stimulation. An antiserum raised against the C-terminus (which in animal Gαs is located near the target coupling site) precipitated Gα without any PLA2 activity. Using non-denaturing PAGE, complexes of solubilized plasma membrane proteins were visualized that contained Gα plus PLA2 activity and dissociated at pH 9.5. At this pH, PLA2 was no longer stimulated by GTPγS. It is concluded that a distinct fraction of the plasma membrane-bound PLA2 exists in a detergent-resistant complex with Gα that can be dissociated at pH 9.5. This complex allows the Gα-mediated activation of PLA2. © 2007 The Authors.