Abstract
The Obg/Era proteins of P-loop GTPase superclass is conserved in various organisms. Some of these proteins are critical regulators in many aspects of cellular processes. However, a genome-wide overview of these genes in plants is not available. Comprehensive genomic analyses of Arabidopsis thaliana identified 19 (in 9 subfamilies) of Obg/Era genes. Subcellular localization of Arabidopsis Obg/Era homologues revealed that archaea-derived proteins are mainly targeted to cytoplasm and nuclei (5). All other eubacteria-related proteins are targeted exclusively to mitochondria (2) or chloroplasts (8) and dual targeting proteins (3), suggesting their endosymbiotic origin. Phylogenetic analysis showed only four proteins that are derived from cyanobacteria by endosymbiotic gene transfer among 11 chloroplast-targeting proteins. Surprisingly, four other chloroplast-targeting GTPases do not show cyanobacterial or α proteobacterial affiliation. Instead, these homologues are closely related to other eubacteria, such as Bacteroides and Green nonsulfur bacteria, suggesting the important role of horizontal gene transfer in chloroplast- and mitochondria localized GTPase evolution.
