EXPRESSION AND CELLULAR-LOCALIZATION OF RAB28 MESSENGER-RNA AND RAB28PROTEIN DURING MAIZE EMBRYOGENESIS

The maize abscisic acid (ABA) responsive gene rab28, has been shown to be ABA-inducible in embryos and vegetative tissues. A polyclonal anti serum was raised against Rab28 protein. Using immunoblotting and immun oprecipitation, the antiserum specifically recognized a protein of abo ut 30 kDa and pl 6 which is in close agreement with the molecular weig ht and pl predicted by the deduced amino acid sequence. The rab28 gene product accumulated during late embryogenesis. In vegetative tissues, dehydration stress induced rab28 gene expression both in the light an d in the dark. The spatial and temporal pattern of rab28 mRNA expressi on during embryogenesis was investigated by in situ hybridization usin g digoxigenin-labelled rab28 probes, and the immunochemical localizati on of Rab28 protein using anti-Rab28 antibodies. Expression of rab28 m RNA is restricted to provascular tissues in young embryos, and at late r stages of development the most prevalent accumulation occurred in me ristem and in the vascular elements of the plumule, root and scutellum . Using immunoelectron microscopy the Rab28 protein has been located i n the nucleolus of different cell types. In light of these results the stress regulation of rab28 and a likely role for this protein during late embryogenesis are discussed.