G proteins are signal transducers found in a variety of eukaryotic organisms, from humans to fruit flies, and from slime molds to yeasts; they are heterotrimers (of alpha, beta, and gamma subunits) that play crucial roles in many types of receptor-mediated signalling processes. In plants, cells respond to a variety of hormonal and environmental stimuli; many of these are known or thought to involve receptors. However, the function of G proteins in plant signal transduction processes has not been demonstrated. This laboratory has recently isolated a gene (GPA1) coding for a G protein alpha subunit (G alpha 1) from the small flowering plant, Arabidopsis thaliana. This is the first G protein gene identified in any plant. The long term goal of this laboratory is to study signal transduction processes in plants which require G protein functions, and to compare and contrast G protein functions between animals, plants and simple eukaryotes. The immediate objective proposed is to characterize the GPA1 gene and its product G alpha 1 in detail. The time and tissue specific patterns of GPA1 expression, the intracellular localization of the G alpha 1 protein, and the function of G alpha 1 in the plant will be examined. A wide range of approaches will be taken; they include transcriptional and translational gene fusions, transgenic plants, analysis using antibodies, and mutational analysis. G proteins are known to be very important in animals and simple eukaryotes. They are necessary for a variety of cellular signalling processes such as hormonal stimulation, photoreception by cells of the retina, chemotaxis of slime molds during aggregation, and the yeast mating response. There is evidence that some plant signal transduction processes also require G proteins, although, thus far, very little is known about this in plants. This laboratory has recently shown that G proteins are present in plants by cloning a gene for a G protein subunit. Understanding the functions of G proteins in plants will be an important contribution to our knowledge of cellular signal transduction processes in plants.
