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

Heterotrimeric GTP-binding (G) proteins are important signaling molecu les found in many eukaryotic organisms. In Arabidopsis thaliana, GPA1 is the only known gene that encodes a G protein a subunit. Results fro m previous experiments indicate that the GPA1 mRNA is found in both ve getative and floral organs of Arabidopsis. To gain insight into the fu nction of GPA1, we sought to obtain detailed information about the dis tribution of the GPA1 gene product. To this end, we have constructed a translational fusion between the GPA1 genomic DNA and the bacterial r eporter gene uidA, encoding beta-glucuronidase (GUS), and introduced i t into Arabidopsis by Agrobacterium-mediated transformation. Histochem ical analysis of the GPA1-uidA transgenic plants shows that GPA1 is ex pressed throughout development from early seedling to the mature flowe ring plant. During seedling development, GPA1 is first expressed in an d near root tips, later also in cotyledons, developing leaves, and muc h of the roots. In adult plants, GPA1 continues to be expressed in ros ette 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 elongati on zone. In mature flowers, carpels exhibit strong GUS staining, where as sepals and stamens have lower GPA1 expression, most of which is in the vascular tissues. Finally, GPA1 is also expressed in developing se eds, 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, different iation, and nutrient transport.