The number of retained mitochondrial protein-coding genes varies widely among eukaryotes, from 67 in the jakobid Reclinomonas americana to only 3 in apicomplexans such as Plasmodium falciparum. The genes encoding many of these proteins were initially encoded within the original respiring endosymbiont but have undergone intracellular transfer to the nucleus over evolutionary time, so that the proteins must be targeted back to the mitochondrion to perform their function. The mitochondrial proteome consists of at least 1000 different proteins. These results illustrate the power of comparative sequencing to identify novel genomic features. Conclusionĭespite the fact that there are now over 20 mitochondrial genome sequences for land plants and green algae, this gene has remained unidentified and largely undetected until now because of the unlikely coincidence that most of the earlier sequences were from the few lineages that lack the intact gene. In several lineages, such as crucifers and grasses, where the rpl10 gene has been lost from the mitochondrion, we suggest that a copy of the nucleus-encoded chloroplast-derived rpl10 gene may serve as a functional replacement. Comparative sequence analysis and distribution of editing suggests that it encodes ribosomal protein L10 of the large subunit of the ribosome. This gene is actively transcribed and RNA edited in many flowering plants. Resultsįrom a broad survey of land plants, we have found that the orf-bryo1 gene is also conserved in the mitochondria of vascular plants and charophycean green algae. However, an ORF, termed orf-bryo1, was recently found to be conserved among bryophytes suggesting that it might indeed encode a functional mitochondrial protein. The lack of wide conservation for most ORFs suggests they are unlikely to be functional.

The mitochondrial genomes of plants generally encode 30-40 identified protein-coding genes and a large number of lineage-specific ORFs.

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