Most cited article - PubMed ID 23361622
Transcription of atp1 is influenced by both genomic configuration and nuclear background in the highly rearranged mitochondrial genomes of Silene vulgaris
Cytoplasmic male sterility (CMS) is a widespread phenomenon in flowering plants caused by mitochondrial (mt) genes. CMS genes typically encode novel proteins that interfere with mt functions and can be silenced by nuclear fertility-restorer genes. Although the molecular basis of CMS is well established in a number of crop systems, our understanding of it in natural populations is far more limited. To identify CMS genes in a gynodioecious plant, Silene vulgaris, we constructed mt transcriptomes and compared transcript levels and RNA editing patterns in floral bud tissue from female and hermaphrodite full siblings. The transcriptomes from female and hermaphrodite individuals were very similar overall with respect to variation in levels of transcript abundance across the genome, the extent of RNA editing, and the order in which RNA editing and intron splicing events occurred. We found only a single genomic region that was highly overexpressed and differentially edited in females relative to hermaphrodites. This region is not located near any other transcribed elements and lacks an open-reading frame (ORF) of even moderate size. To our knowledge, this transcript would represent the first non-coding mt RNA associated with CMS in plants and is, therefore, an important target for future functional validation studies.
- Keywords
- Cytoplasmic male sterility, Silene vulgaris, editing, mitochondrion, non-coding RNA, splicing, transcriptome.,
- MeSH
- RNA Editing MeSH
- Flowers genetics growth & development MeSH
- Genes, Mitochondrial * MeSH
- RNA, Untranslated * MeSH
- Plant Infertility * MeSH
- Plant Proteins genetics metabolism MeSH
- Silene genetics physiology MeSH
- Transcriptome * MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Names of Substances
- RNA, Untranslated * MeSH
- Plant Proteins MeSH
BACKGROUND: Species within the angiosperm genus Silene contain the largest mitochondrial genomes ever identified. The enormity of these genomes (up to 11 Mb in size) appears to be the result of increased non-coding DNA, which represents >99 % of the genome content. These genomes are also fragmented into dozens of circular-mapping chromosomes, some of which contain no identifiable genes, raising questions about if and how these 'empty' chromosomes are maintained by selection. To assess the possibility that they contain novel and unannotated functional elements, we have performed RNA-seq to analyze the mitochondrial transcriptome of Silene noctiflora. RESULTS: We identified regions of high transcript abundance in almost every chromosome in the mitochondrial genome including those that lack any annotated genes. In some cases, these transcribed regions exhibited higher expression levels than some core mitochondrial protein-coding genes. We also identified RNA editing sites throughout the genome, including 97 sites that were outside of protein-coding gene sequences and found in pseudogenes, introns, UTRs, and transcribed intergenic regions. Unlike in protein-coding sequences, however, most of these RNA editing sites were only edited at intermediate frequencies. Finally, analysis of mitochondrial small RNAs indicated that most were likely degradation products from longer transcripts, but we did identify candidates for functional small RNAs that mapped to intergenic regions and were not associated with longer RNA transcripts. CONCLUSIONS: Our findings demonstrate transcriptional activity in many localized regions within the extensive intergenic sequence content in the S. noctiflora mitochondrial genome, supporting the possibility that the genome contains previously unidentified functional elements. However, transcription by itself is not proof of functional importance, and we discuss evidence that some of the observed transcription and post-transcriptional modifications are non-adaptive. Therefore, further investigations are required to determine whether any of the identified transcribed regions have played a functional role in the proliferation and maintenance of the enormous non-coding regions in Silene mitochondrial genomes.
- MeSH
- RNA Editing MeSH
- Genome, Mitochondrial * MeSH
- Genome, Plant * MeSH
- DNA, Intergenic MeSH
- RNA, Messenger MeSH
- Open Reading Frames MeSH
- Pseudogenes MeSH
- RNA, Mitochondrial MeSH
- RNA MeSH
- Genes, Plant MeSH
- Sequence Analysis, RNA MeSH
- Silene genetics MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Names of Substances
- DNA, Intergenic MeSH
- RNA, Messenger MeSH
- RNA, Mitochondrial MeSH
- RNA MeSH
We review current studies of plant mitochondrial transcriptomes performed by RNA-seq, highlighting methodological challenges unique to plant mitochondria. We propose ways to improve read mapping accuracy and sensitivity such as modifying a reference genome at RNA editing sites, using splicing- and ambiguity-competent aligners, and masking chloroplast- or nucleus-derived sequences. We also outline modified RNA-seq methods permitting more accurate detection and quantification of partially edited sites and the identification of transcription start sites on a genome-wide scale. The application of RNA-seq goes beyond genome-wide determination of transcript levels and RNA maturation events, and emerges as an elegant resource for the comprehensive identification of editing, splicing, and transcription start sites. Thus, improved RNA-seq methods customized for plant mitochondria hold tremendous potential for advancing our understanding of plant mitochondrial evolution and cyto-nuclear interactions in a broad array of plant species.
