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BMC Genomics  2011 

Transcriptome map of plant mitochondria reveals islands of unexpected transcribed regions

DOI: 10.1186/1471-2164-12-279

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Abstract:

Whereas statistical analysis verified the transcription of all previously known functional genes such as the ones related to oxidative phosphorylation, a similar extent of RNA expression was frequently observed in the inter-genic regions where none of the previously annotated genes are located. The newly identified open reading frames (ORFs) predicted in these transcribed inter-genic regions were generally not conserved among flowering plant species, suggesting that these ORFs did not play a role in mitochondrial principal functions. We also identified two partial fragments of retrotransposon sequences as being transcribed in rice mitochondria.The present study indicated the previously unexpected complexity of plant mitochondrial RNA metabolism. Our transcriptomic data (Oryza sativa Mitochondrial rna Expression Server: OsMES) is publicly accessible at [http://bioinf.mind.meiji.ac.jp/cgi-bin/gbrowse/OsMes/#search webcite].The obvious expansion of its genomic size indicates that higher plant mitochondria experienced a dramatic evolution. The common size of mitochondria genetic information is limited to approximately 16 kb in metazoans [1], whereas in higher plants the sequence length can be 200-2400 kb (Additional file 1) [2]. The principal role of mitochondria (i.e. oxidative phosphorylation) is undoubtedly shared between metazoans and higher plants. The presence of three genes encoding subunits of ATP synthase (atp6 and atp8), three genes encoding subunits of cytochrome oxidase (cox1-cox3), cytochrome b (cob), and seven genes for NADH dehydrogenase (nad1-nad4, nad4L, nad5 and nad6) is indeed conserved in mitochondria of both kingdoms. What is extra in plant mitochondria compared to that of metazoans are only a few more respiratory-related genes (including atp1, atp9, nad7 and nad9) and dozens of genes encoding ribosomal subunits (rps or rpl). Thus, usually a higher plant mitochondrion encodes about 40 genes with known functions, whereas in most cases there are 13 ti

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