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

doi:10.1073/pnas.0712299105

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

*Institut de Biologie Moléculaire des Plantes (Unité Propre de Recherche 2357 du Centre National de la Recherche Scientifique), 12 Rue du Général Zimmer, Université Louis Pasteur-Strasbourg 1, Centre National de la Recherche Scientifique, F-67084 Strasbourg Cedex, France; and
^†UPR Architecture et Réactivité de l'ARN (UPR 9002 du Centre National de la Recherche Scientifique), Institut de Biologie Moléculaire et Cellulaire, 15 Rue René Descartes, Université Louis Pasteur-Strasbourg 1, Centre National de la Recherche Scientifique, F-67084 Strasbourg, France

Edited by Paul R. Schimmel, The Scripps Research Institute, La Jolla, CA, and approved February 4, 2008 (received for review December 28, 2007)

Abstract

Aminoacyl-tRNAs are generally formed by direct attachment of an amino acid to tRNAs by aminoacyl-tRNA synthetases, but Gln-tRNA is an exception to this rule. Gln-tRNA^Gln is formed by this direct pathway in the eukaryotic cytosol and in protists or fungi mitochondria but is formed by an indirect transamidation pathway in most of bacteria, archaea, and chloroplasts. We show here that the formation of Gln-tRNA^Gln is also achieved by the indirect pathway in plant mitochondria. The mitochondrial-encoded tRNA^Gln, which is the only tRNA^Gln present in mitochondria, is first charged with glutamate by a nondiscriminating GluRS, then is converted into Gln-tRNA^Gln by a tRNA-dependent amidotransferase (AdT). The three subunits GatA, GatB, and GatC are imported into mitochondria and assemble into a functional GatCAB AdT. Moreover, the mitochondrial pathway of Gln-tRNA^Gln formation is shared with chloroplasts as both the GluRS, and the three AdT subunits are dual-imported into mitochondria and chloroplasts.

Footnotes

^‡To whom correspondence may be addressed. E-mail: anne-marie.duchene{at}ibmp-ulp.u-strasbg.fr or h.becker{at}ibmc.u-strasbg.fr
Author contributions: A.-M.D. designed research; C.P., M.B., and A.-M.D. performed research; C.P., M.B., D.K., L.M.-D., H.B., and A.-M.D. analyzed data; and H.B. and A.-M.D. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0712299105/DCSupplemental.