"Melting pot" of plant tRNAs and aminoacyl-tRNA-synthetases

Complexity of plants on the cellular level includes the existance of three separate genomes that require functioning of three distinct translational machineries, in cytosol, mitochondria and plastids. Interplay of the nucleus and the organelles during the evolution of a plant cell gave rise to the unusual diversity of evolutionary origin and cellular localization of tRNAs and aminoacyl-tRNA synthetases. Aminoacyl-tRNA synthetases are enzymes that participate in the translation process linking amino acid to its cognate tRNA. Many aminoacyl-tRNA synthetases are dual targeted and therefore function in two cellular compartments, either in mitochondria and cytosol, or in mitochondria and plastids. In most cases, this dual targeting is associated with the peculiar evolutionary origin of plant mitochondrial tRNAs. These can be native mitochondrial tRNAs, tRNAs of plastid origin and nucleus-encoded tRNAs imported from the cytosol. Our biochemical studies and computer predictions imply that of the two maize seryl-tRNA synthetases, one functions in the cytosol, and the other is dual targeted to maize mitochondria and plastids. This dual targeting can be explained by common bacterial characteristics of mitochondrial and plastid tRNAs^Ser that originate from their endosymbiotic origins.