Expression and cellular localization of Atrab28 during Arabidopsis embryogenesis

The maize abscisic acid (ABA)-responsive gene rab28 has been shown to be AB A-inducible in embryos and vegetative tissues, expression being mostly rest ricted to vascular elements during late embryogenesis. In the course of an expressed sequence tags (ESTs) programme, we have isolated an Arabidopsis t haliana gene, Atrab28, encoding the orthologue of maize rab28. The Atrab28 cDNA is 1090 bp long, including a poly(A)(+) stretch, and encodes a polypep tide of 262 amino acids. Atrab28 antibody against the recombinant protein r ecognizes a polipeptide of about 30 kDa and pI 6, in close agreement with t he predicted molecular mass and pI. As for maize rab28, expression studies with Atrab28 revealed high specificity for embryo tissues, transcription be ing 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 wa s largely restricted to provascular tissues of mature embryos and in the se ed coat outer tegument and embryo and silique epidermis, as revealed by in situ hybridization and immunocytochemistry with anti-Atrab28 antibodies.