ABSTRACT
Different lines of evidence suggest that specific events during the cell cycle may be mediated by a heterotrimeric G-protein activated by a cognate G-protein coupled receptor. However, coupling between the only known Galpha-subunit of the heterotrimeric G-protein (GPA1) and the only putative G-protein coupled receptor (GCR1) of plants has never been shown. Using a variety of approaches, we show here that GCR1-enhanced thymidine incorporation into DNA depends on an increase in phosphatidylinositol-specific phospholipase C activity and an elevation of inositol 1,4,5-trisphosphate levels in the cells. Tobacco (Nicotiana tabacum) cells that overexpress either Arabidopsis GCR1 or GPA1 display this phenomenon. We suggest on the basis of these results that GCR1-controlled events during the cell cycle involve phosphatidylinositol-specific phospholipase C as an effector of GCR1 and inositol 1,4,5-trisphosphate as a second messenger, and that GCR1 and GPA1 are both involved in this particular signaling pathway.
Subject(s)
Arabidopsis Proteins/metabolism , DNA Replication/genetics , Phosphatidylinositol Diacylglycerol-Lyase/metabolism , Receptors, G-Protein-Coupled/metabolism , Cloning, Molecular , DNA, Plant/biosynthesis , Enzyme Activation , Enzyme Inhibitors/pharmacology , Estrenes/pharmacology , Inositol 1,4,5-Trisphosphate/metabolism , Models, Biological , Phosphatidylinositol Diacylglycerol-Lyase/antagonists & inhibitors , Phosphoinositide Phospholipase C , Phosphorylation , Protein Kinase C/metabolism , Pyrrolidinones/pharmacology , Recombinant Proteins/metabolism , Signal Transduction , Thymidine/metabolism , Nicotiana/metabolism , Transcription Factors/metabolismABSTRACT
Although signaling through heterotrimeric G proteins has been extensively studied in eukaryotes, there is little information about this important signaling pathway in plants. We observed that expression of GCR1, the gene encoding the only known (but still putative) G protein-coupled receptor of Arabidopsis thaliana, is modulated during the cell cycle and during plant development. Overexpression of GCR1 in tobacco (Nicotiana tabacum) BY-2 cells caused an increase in thymidine incorporation and in the mitotic index of aphidicolin synchronized cells. Overexpression of GCR1 in Arabidopsis caused two remarkable phenotypes: seed dormancy was abolished and time to flowering was reduced. Molecular markers of these two developmental processes (phosphatase PP2A and MYB65 in germination; LFY during flowering) were up-regulated in GCR1 overexpressors. These data are consistent with the hypothesis that GCR1 may be a regulator of the cell cycle and that this regulation underlies the developmental changes observed in the GCR1 transformants.
