PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

The plastid targeted GTP-binding protein, AtOBG1 is essential for embryo development in Arabidopsis. Tetsuya Umeda^*,1, Yoichi Nakahira¹, Go Takeba¹, Takashi Shiina¹, ¹ Faculty of Human and Environment, Kyoto City, Japan

ABSTRACT- Obg and Era are members of small GTP-binding proteins that are essential to bacterial growth. The Obg/Era homologues have been identified in diverse organisms ranging from bacteria to eukaryotes including human and higher plants. It has been proposed that the bacterial Obg/Era are involved in various cellular processes such as chromosome partitioning, translation and stress-activation of transcription factor sigma B. However, the biological function of Obg/Era homologues in higher organisms remains largely unknown. Arabidopsis contains two Obg/Era homologue genes (AtOBG1 and AtOBG2) of which products are predicted to localize in chloroplasts. The AtOBG1 shows overall homology to Bacillus Obg except for the N-terminal 220 amino acids extension. Transient expression assays using green fluorescent protein (GFP) demonstrated that the N-terminal extension of the AtOBG1 could function as a chloroplast transit peptides. Furthermore, the full length AtOBG1::GFP fusion protein was present as a few discrete fluorescent dots in chloroplasts. The AtOBG1 transcripts were accumulated preferentially in leaves in a light-dependent manner. Knockout of the AtOBG1 gene produced a defect in embryo development before the heart stage. These results suggest that AtOBG1 is an essential gene in Arabidopsis as in the case of bacterial Obg/Era members and the AtOBG1 protein may play a crucial role in chloroplast functioning.

KEY WORDS: Obg/Era family, GTP-binding protein, embryo lethal, plastid