title: Evidence for lateral gene transfer (LGT) in the evolution of eubacteria-derived small GTPases in plant organelles.
abstract: The genomes of free-living bacteria frequently exchange genes via lateral gene transfer (LGT), which has played a major role in bacterial evolution. LGT also played a significant role in the acquisition of genes from non-cyanobacterial bacteria to the lineage of "primary" algae and land plants. Small GTPases are widely distributed among prokaryotes and eukaryotes. In this study, we inferred the evolutionary history of organelle-targeted small GTPases in plants. Arabidopsis thaliana contains at least one ortholog in seven subfamilies of OBG-HflX-like and TrmE-Era-EngA-YihA-Septin-like GTPase superfamilies (together referred to as Era-like GTPases). Subcellular localization analysis of all Era-like GTPases in Arabidopsis revealed that all 30 eubacteria-related GTPases are localized to chloroplasts and/or mitochondria, whereas archaea-related DRG and NOG1 are localized to the cytoplasm and nucleus, respectively, suggesting that chloroplast- and mitochondrion-localized GTPases are derived from the ancestral cyanobacterium and α-proteobacterium, respectively, through endosymbiotic gene transfer (EGT). However, phylogenetic analyses revealed that plant organelle GTPase evolution is rather complex. Among the eubacterium-related GTPases, only four localized to chloroplasts (including one dual targeting GTPase) and two localized to mitochondria were derived from cyanobacteria and α-proteobacteria, respectively. Three other chloroplast-targeted GTPases were related to α-proteobacterial proteins, rather than to cyanobacterial GTPases. Furthermore, we found that four other GTPases showed neither cyanobacterial nor α-proteobacterial affiliation. Instead, these GTPases were closely related to clades from other eubacteria, such as Bacteroides (Era1, EngB-1, and EngB-2) and green non-sulfur bacteria (HflX). This study thus provides novel evidence that LGT significantly contributed to the evolution of organelle-targeted Era-like GTPases in plants.
authors.affiliation: Graduate School of Biostudies, Kyoto University Kyoto, Japan ; Department of Biology, Faculty of Science, Tadulako University Palu, Indonesia.
authors.forename: I Nengah
authors.initials: IN
authors.lastname: Suwastika
authors.affiliation: Graduate School of Biostudies, Kyoto University Kyoto, Japan ; Graduate School of Medicine, Kyoto University Kyoto, Japan.
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Denawa
authors.affiliation: Graduate School of Life and Environmental Sciences, Kyoto Prefectural University Kyoto, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Yomogihara
authors.affiliation: Division of Life Science (BK21 plus program), Graduate School of Gyeongsang National University Jinju, South Korea.
authors.forename: Chak Han
authors.initials: CH
authors.lastname: Im
authors.affiliation: Division of Life Science (BK21 plus program), Graduate School of Gyeongsang National University Jinju, South Korea.
authors.forename: Woo Young
authors.initials: WY
authors.lastname: Bang
authors.affiliation: Division of Biomedical Science, Faculty of Medicine, University of Tsukuba Tsukuba, Japan.
authors.forename: Ryosuke L
authors.initials: RL
authors.lastname: Ohniwa
authors.affiliation: Division of Life Science (BK21 plus program), Graduate School of Gyeongsang National University Jinju, South Korea.
authors.forename: Jeong Dong
authors.initials: JD
authors.lastname: Bahk
authors.affiliation: Graduate School of Biostudies, Kyoto University Kyoto, Japan.
authors.forename: Kunio
authors.initials: K
authors.lastname: Takeyasu
authors.affiliation: Graduate School of Life and Environmental Sciences, Kyoto Prefectural University Kyoto, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Shiina
keywords: endosymbiotic gene transfer; evolution of organelle; genomic analysis; lateral gene transfer; small GTPase