Abstract
The Obg subfamily of monomeric GTPases has been identified in most organisms including bacteria, mammals and plants. Bacterial Obg proteins seem to play a specialized role in ribosome function. However, the molecular function of eukaryotic Obg proteins is largely unknown. Prokaryotes have one Obg protein, whereas eukaryotes posses several homologues, suggesting that each eukaryotic Obg protein may function in different organelles. We identified two Obg homologues (AtObg1 and AtObg2) in Arabidopsis. AtObg1 carries a potential chloroplast transit peptide at N termini. To confirm its subcellular localization, stable transgenic plants expressing AtObg1-GFP fusion proteins were examined with confocal microscopy. The AtObg1-GFP fusion proteins are localized in the chloroplast in all tissues, including leaves and roots. Knockout of AtOBG1 gene resulted in a defect in embryo development. On the other hand, AtObg1 over-expression lines showed variegated phenotypes. These results suggest that AtObg1 may play a crucial role in ribosomal function in chloroplasts.
