REGULATED EXPRESSION OF THE ARABIDOPSIS G-PROTEIN ALPHA-SUBUNIT GENE GPA1

Heterotrimeric GTP-binding (G) proteins are important signaling molecules found in many eukaryotic organisms. In Arabidopsis thaliana, GPA1 is the only known gene that encodes a G protein a subunit. Results from previous experiments indicate that the GPA1 mRNA is found in both vegetative and floral organs of Arabidopsis. To gain insight into the function of GPA1, we sought to obtain detailed information about the distribution of the GPA1 gene product. To this end, we have constructed a translational fusion between the GPA1 genomic DNA and the bacterial reporter gene uidA, encoding beta-glucuronidase (GUS), and introduced it into Arabidopsis by Agrobacterium-mediated transformation. Histochemical analysis of the GPA1-uidA transgenic plants shows that GPA1 is expressed throughout development from early seedling to the mature flowering plant. During seedling development, GPA1 is first expressed in and near root tips, later also in cotyledons, developing leaves, and much of the roots. In adult plants, GPA1 continues to be expressed in rosette and cauline leaves, floral stems, and roots. The GPA1 expression in these vegetative organs is higher in the vascular tissues, as well as the newly formed portions of roots including root tips and elongation zone. In mature flowers, carpels exhibit strong GUS staining, whereas sepals and stamens have lower GPA1 expression, most of which is in the vascular tissues. Finally, GPA1 is also expressed in developing seeds, but the expression diminishes gradually to undetectable levels as the seeds mature. Our results on GPA1 expression indicate that it may be involved in a number of processes including cell growth, differentiation, and nutrient transport.