To identify region(s) of the mitochondrial genome that might be involved in specifying the "Polima" (pol) cytoplasmic male sterility (CMS) of Brassica napus, transcripts corresponding to 14 mitochondrial genes and DNA clones representing $>$90% of the mitochondrial genome of Brassica campestris were analyzed in nap (male fertile), pol (male sterile) and nuclear fertility-restored pol cytoplasm plants. CMS-correlated transcriptional differences among these plants were detected only with the ATPase subunit 6 (atp6) gene. Sequence analysis of the atp6 gene regions of pol and nap mitochondrial DNAs show that rearrangements in the pol mitochondrial genome upstream of atp6 have generated a chimeric 224-codon open reading frame, designated orfJ224, that is cotranscribed with atp6. In male sterile plants, most transcripts of this region are dicistronic, comprising both orf224 and atp6 sequences. In fertility restored-plants, genes at either of two distinct nuclear restorer loci specifically alter this transcript pattern, resulting in predominantly monocistronic atp6 transcripts. The effect of the restorer locus on orf224/atp6 transcripts does not seem to be tissue or developmental stage specific. orf224 comprises a portion of the mitochondrial gene, orfB, fused to sequence of unknown origin. The pol mitochondrial genome contains an apparently functional copy of orfB. The expression of the atp6 region is developmentally regulated in pol plants such that levels of monocistronic atp6 transcripts are increased in seedlings as compared to the floral tissue. Preliminary data indicate that the chimeric gene, orf224, is expressed at the protein level in pol plants.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.39754 |
| Date | January 1992 |
| Creators | Singh, Mahipal |
| Contributors | Brown, Gregory G. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001327449, proquestno: NN87543, Theses scanned by UMI/ProQuest. |
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