Characterization of Open Reading Frames in the Tobacco Mitochondrial Transcriptome

Abstract

Initial annotation of the tobacco mitochondrial genome in 2005 identified numerous identifiable protein coding, tRNA, and rRNA genes plus 119 open reading frames (ORFs) with no clearly stated function. The purpose of this study was to explore expression of putative open reading frames in the Nicotiana tabacum mitochondrial genome. I surmised that if these gene products are transcribed and translated they may have a functional role in the tobacco mitochondria. In this study, these ORFs were screened for expression using RNA deep sequencing, qRT-PCR, and polysome analysis. Twenty-five of the 119 were found to have steady-state RNA amounts above background and 15 of those were found to be polysome associated. These ORFs were also bioinformatically compared to other genes. Some of the transcribed ORFs were found to be fragments of mitochondrial proteins, some were not identifiable while some were homologous to plastid or nuclear coding genes. Five of the expressed ORFs have been linked to cytoplasmic male sterility in other plants. The 10 remaining ORFs found to be polysome-associated have the potential to be novel mitochondrial proteins.