Evolution of a mitochondrial tRNA PHE gene in A. thaliana: import of cytosolic tRNA PHE into mitochondria.

Previously we have described a putative tRNATyr in Arabidopsis thaliana mitochondria, the sequence of which is different from that of other plant mitochondrial tRNATyr genes. We show here that this tRNATyr gene sequence is present in several copies in the mitochondrial genome of A. thaliana. One copy of these tRNATyr gene sequences, termed here tRNATyr-1, could encode a functional tRNA. Expression analysis has shown that the tRNATyr-1 gene is cotranscribed with the downstream tRNAGlu gene, and that the corresponding mature-sized tRNA is present in mitochondria. We also show that the native tRNATyr gene, similar to the mitochondrial tRNATyr genes found in plants, is present in the A. thaliana mitochondrial genome and expressed. The tRNATyr-1 gene has been previously suggested to be derived from a tRNAPhe gene sequence. We show here that, as a consequence, there is no tRNAPhe gene in the mitochondrial genome of A. thaliana and that a cytosolic tRNAPhe is imported in A. thaliana mitochondria.