CLONING AND CHARACTERIZATION OF RAC-LIKE CDNAS FROM ARABIDOPSIS-THALIANA

The Rho family of GTPases are in higher eukaryotes divided into 3 majo r subfamilies; the Rho, Rac and Cdc42 proteins. In plants, however, th e Rho family is restricted to one large family of Rac-like proteins. F rom work with mammalian phagocytes the Rac proteins are known to activ ate a multicomponent NADPH-dependent oxidase which results in accumula tion of H2O2, a process termed oxidative burst. In plants a similar ox idative burst is observed and plays an important role in its defence a gainst pathogen infections, suggesting a similar role for the plant Ra c-like proteins. The Rho family of GTPases proteins are also involved in control of cell morphology, and are also thought to mediate signals from cell membrane receptors. In a broad search for members of the Ra s superfamily in plants, several new small GTP-binding proteins were f ound. We report here the identification and molecular cloning of 5 rac -like cDNAs from Arabidopsis thaliana, Arac1-5. The Rac-like proteins deduced from the cDNA sequences all share 80-95% homology, but show co nsiderably more diversity on the nucleotide level, indicating that thi s is an ancient gene family. Four of the rac genes were found to be ex pressed in all tissues examined, but one gene, Arac2, was expressed ex clusively in the root, hypocotyl and stem. Our results show that the r ac gene family in A. thaliana consists of at least 10 different genes.