Abstract
BackgroundAn 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.ResultsThe 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.ConclusionsIt 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.
Highlights
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
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
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
Summary
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. Mitochondria in plants contain many unique features compared to their fungal or animal counterparts These include a larger genome, ranging from 200 Kb to 2000 Kb in size [11], extensive cis and trans splicing of introns, [12], relatively slow rates of mutations [13,14], extensive editing of mRNA [15] and incorporation of foreign DNA [16]. Another notable feature is the presence of a branched respiratory chain [17]. Mitochondria of plants and animals have diversified in a lineage specific manner to include or exclude various biochemical pathways, such as the b-oxidation of fatty acids that occurs in peroxisomes in plants and mitochondria in animals [19]
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