Expression and cellular localization of Atrab28 during Arabidopsis embryogenesis

The maize abscisic acid (ABA)-responsive gene rab28 has been shown to be ABA-inducible in embryos and vegetative tissues, expression being mostly restricted to vascular elements during late embryogenesis. In the course of an expressed sequence tags (ESTs) programme, we have isolated an Arabidopsis thaliana gene, Atrab28, encoding the orthologue of maize rab28. The Atrab28 cDNA is 1090 bp long, including a poly(A)+ stretch, and encodes a polypeptide of 262 amino acids. Atrab28 antibody against the recombinant protein recognizes a polipeptide of about 30 kDa and pI 6, in close agreement with the predicted molecular mass and pI. As for maize rab28, expression studies with Atrab28 revealed high specificity for embryo tissues, transcription being stimulated by the transcriptional activator abi3. In contrast, Atrab28 was not induced in vegetative tissues by ABA, osmotic stress or dehydration. The expression of Atrab28 mRNA and the accumulation of Atrab28 protein was largely restricted to provascular tissues of mature embryos and in the seed coat outer tegument and embryo and silique epidermis, as revealed by in situ hybridization and immunocytochemistry with anti-Atrab28 antibodies.This work was supported by a joint programme between the CNRS (Centre National de la Recherche Scientifique) and the CSIC (Consejo Superior de Investigaciones Científicas), the European Associated Laboratory between Perpignan and Barcelona in Plant Molecular and Cellular Biology. In addition, both Perpignan and Barcelona groups are members of the European project ‘Characterising and engineering abscisic acid action’ (Biotech BIO4-CT96-0062). Work in Barcelona was supported in part by the European Communities Biotech Programme, as part of the Project of Technological Priority and by grant BIO94-0750 from Plan Nacional de Investigatión Científica y Desarrollo Tecnológico. Work in Perpignan was supported by CNRS grants URA 565 and UMR 5545.Peer reviewe