Dual targeting is the rule for organellar aminoacyl-tRNA synthetases in Arabidopsis thaliana

Abstract

In plants, protein synthesis occurs in the cytosol, mitochondria, and plastids. Each compartment requires a full set of tRNAs and aminoacyl-tRNA synthetases. We have undertaken a systematic analysis of the targeting of organellar aminoacyl-tRNA synthetases in the model plant Arabidopsis thaliana. Dual targeting appeared to be a general rule. Among the 24 identified organellar aminoacyltRNA synthetases (aaRSs), 15 (and probably 17) are shared between mitochondria and plastids, and 5 are shared between cytosol and mitochondria (one of these aaRSs being present also in chloroplasts). Only two were shown to be uniquely chloroplastic and none to be uniquely mitochondrial. Moreover, there are no examples where the three aaRS genes originating from the three ancestral genomes still coexist. These results indicate that extensive exchange of aaRSs has occurred during evolution and that many are now shared between two or even three compartments. The findings have important implications for studies of the translation machinery in plants and on protein targeting and gene transfer in general.GFP ͉ mitochondria ͉ plastids ͉ protein targeting ͉ translation

Dual-targeted tRNA-dependent amidotransferase ensures both mitochondrial and chloroplastic Gln-tRNA Gln synthesis in plants

“…The A. thaliana nuclear genome encodes two GluRSs. The protein encoded by one GluRS gene (At5g64050) has been shown to be imported into both plant mitochondria and chloroplasts, and the second GluRS (At5g26710) is expected to be cytosolic (8). Aminoacylation assays show that GluRS activities can be detected in the total (mostly representing the cytosolic GluRS activity) and mitochondrial extracts in A. thaliana (Fig.…”

“…During evolution, most mitochondrial and chloroplastic protein genes have been lost or transferred to the nucleus. The present-time organellar GluRS, GatA, and GatB subunits are clearly related to their cyanobacterial counterparts (8) (Figs. S2 and S3), suggesting that the ancestral chloroplastic pathway was kept during evolution as the mitochondrial one was lost.…”

“…Approximately 40 examples of dual-targeted proteins of the thousands of organellar-imported proteins have been identified in A. thaliana, but half of these proteins correspond to aaRSs (11). Eighteen of 24 identified A. thaliana organellar aaRSs are shared between mitochondria and chloroplasts (8,18). The dual localization of GatCAB gives an example of cross-compartment sharing of enzymes involved in aa-tRNA synthesis.…”

Caracterização do papel da glutamil-tRNA sintetase na localização subcelular de proteínas

“…Ao longo do tempo, os organismos eucariotos desenvolveram vias complexas de direcionamento de proteínas para seus diversos compartimentos celulares. Em plantas, as estimativas apontam para milhares de proteínas codificadas por genes nucleares que são sintetizadas nos ribossomos e transportadas para mitocôndrias e cloroplastos, onde são ativas (HEAZLEWOOD et al, 2005 Um exemplo bem estudado de proteínas com DD vem da família das aminoaciltRNA sintetases (aaRS) (DUCHÊNE et al, 2005). Estas proteínas têm como função canônica acoplar o tRNA com seu aminoácido cognato durante a síntese protéica.…”

“…Em Arabidopsis, há dois genes nucleares para a GluRS, um deles (At5g64050) codifica uma GluRS de DD de 570 aminoácidos (DUCHÊNE et al, 2005) Baseando-se nestas informações, este estudo teve como objetivo principal verificar um possível papel da GluRS de Arabidopsis thaliana na regulação da localização subcelular de proteínas, sobretudo aquelas de DD. Mais especificamente, este estudo visa identificar e caracterizar interações entre a GluRS citosólica (At5g26710) e proteínas de DD através de bibliotecas de cDNA de Arabidopsis thaliana inseridas no sistema duplo-híbrido de levedura; mapear a(s) região(ões) onde ocorre a interação entre as proteínas através de deleções; confirmar a interação entre as proteínas in vivo in planta por microscopia usando complementação fluorescente bimolecular (sistema BiFC); analisar filogeneticamente a região N-terminal da GluRS, esclarecendo sua origem e datação.…”