The structure of one member of a family of maize mitochondrial RNA replicons (or RNA plasmids), RNA b, has been characterized. It is shown that RNA b shares a 13 nucleotide sequence with the central conserved region of Cadang-Cadang viroid of coconuts which might be involved in substrate recognition by the RNA replicase during replication. RNA b likely was derived from a larger member in that family, RNA a, through co-linear deletions similar to those involved with the generation of the defective interfering (DI) elements associated with both animal and plant viruses. RNA b may represent a "selfish" RNA optimized for replication as it does not have the capacity to encode its own replicase. Mitochondrial RNA plasmids have been found not to be restricted to the S and RU cytoplasms, as previously reported. Related plasmid RNAs have been detected in maize plants with C, N and T cytoplasms as well as 13 Latin American races. They were not found, however, in teosintes, indicating that the ancestral nucleic acid from which these RNAs evolved was acquired soon after the split between teosintes and maize, before the divergence of the maize races. Distribution of the plasmid RNAs, a maize mRNA (atp6), and a mitochondrial rRNA (26S) in different organs and tissues was investigated by in situ hybridization. These results indicated that mitochondrial gene expression is subjected to an unexpected degree of both spatial and developmental regulation, and that individual mitochondrial genes are subjected to different controls. Similar results were obtained in in situ hybridization studies of Brassica floral buds. Both studies suggested that the levels of mitochondrial genes transcripts are not particularly high in the tapetal cells of both maize and Brassica anthers contrary to common belief. High levels of RNA plasmid were detected in the pollen of S maize anthers prior to pollen abortion, suggesting they might be related to the cytoplasmic male sterility (CMS) trait of S maize
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41804 |
| Date | January 1993 |
| Creators | Zhang, Mingda |
| 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: 001396082, proquestno: NN94731, Theses scanned by UMI/ProQuest. |
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