title: An in silico analysis of the mitochondrial protein import apparatus of plants.
abstract: BACKGROUND
  An in silico analysis of the mitochondrial protein import apparatus from a variety of species; including Chlamydomonas reinhardtii, Chlorella variabilis, Ectocarpus siliculosus, Cyanidioschyzon merolae, Physcomitrella patens, Selaginella moellendorffii, Picea glauca, Oryza sativa and Arabidopsis thaliana was undertaken to determine if components differed within and between plant and non-plant species.
  
  
  RESULTS
  The channel forming subunits of the outer membrane components Tom40 and Sam50 are conserved between plant groups and other eukaryotes. In contrast, the receptor component(s) in green plants, particularly Tom20, (C. reinhardtii, C. variabilis, P. patens, S. moellendorffii, P. glauca, O. sativa and A. thaliana) are specific to this lineage. Red algae contain a Tom22 receptor that is orthologous to yeast Tom22. Furthermore, plant mitochondrial receptors display differences between various plant lineages. These are evidenced by distinctive motifs in all plant Metaxins, which are absent in red algae, and the presence of the outer membrane receptor OM64 in Angiosperms (rice and Arabidopsis), but not in lycophytes (S. moellendorffii) and gymnosperms (P. glauca). Furthermore, although the intermembrane space receptor Mia40 is conserved across a wide phylogenetic range, its function differs between lineages. In all plant lineages, Tim17 contains a C-terminal extension, which may act as a receptor component for the import of nucleic acids into plant mitochondria.
  
  
  CONCLUSIONS
  It is proposed that the observed functional divergences are due to the selective pressure to sort proteins between mitochondria and chloroplasts, resulting in differences in protein receptor components between plant groups and other organisms. Additionally, diversity of receptor components is observed within the plant kingdom. Even when receptor components are orthologous across plant and non-plant species, it appears that the functions of these have expanded or diverged in a lineage specific manner.
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, 35 Stirling, Crawley 6009, WA, Australia.
authors.forename: Chris
authors.initials: C
authors.lastname: Carrie
authors.forename: Monika W
authors.initials: MW
authors.lastname: Murcha
authors.forename: James
authors.initials: J
authors.lastname: Whelan
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D002708:Chlorella / Q000235:genetics / Q000378:metabolism; D014644:Genetic Variation; D026901:Membrane Transport Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics / Q000378:metabolism; D000459:Phaeophyceae / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D028222:Picea / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport; D000461:Rhodophyta / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment / Q000379:methods; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D010940:Plant Proteins