ATGDI2, A NOVEL ARABIDOPSIS GENE ENCODING A RAB GDP DISSOCIATION INHIBITOR

The GTPase cycle of Rab/Ypt proteins is strictly controlled by several classes of regulators to ensure their proper roles in membrane traffi c. GDP dissociation inhibitor (GDI) is known to play essential roles i n regulating nucleotide states and subcellular localizations of Rab/Yp t proteins. To obtain further knowledge on this regulator molecule in plants, we isolated and characterized two genes of Arabidopsis thalian a that encode different GDIs. AtGDI1 has been identified by a novel fu nctional cloning in yeast [Ueda et al. (1996) Plant Cell, 8, 2079-2091 ] and AtGDI2 was isolated by cross-hybridization in this study. AtGDI2 , as well as AtGDI1, complements the yeast sec19/gdi1 mutant, indicati ng that they can replace the function of yeast GDI. Evidence is shown that both AtGDI1 and AtGDI2 can interact with Ara4, an Arabidopsis Rab protein, in the yeast ypt1 mutant cells. AtGDI2 is ubiquitously expre ssed in Arabidopsis tissues with some difference from AtGDI1 in expres sion level. Genomic DNA hybridization using specific probes reveals th e presence of one more GDI gene in Arabidopsis. This may imply differe ntiated roles of GDI in higher plants. (C) 1997 Elsevier Science B.V.