No description available.

No description available.

Thesis (Ph. D.)--University of Chicago, Dept. of Molecular Genetics and Cell Biology, August 1999. / Includes bibliographical references. Also available on the Internet.

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

Previous studies have shown that transcriptional differences in the orf224-atp6 mitochondrial gene region are correlated with fertility restoration of the pol CMS trait by the dominant nuclear Rfp gene in Brassica napus. Recently, the recessive rfp allele, or a tightly linked gene, was found to act as a dominant gene, designated Mmt, in controlling the production of additional, smaller transcripts of two other mitochondrial loci. The results presented in this thesis reveal that Mmt-specific transcripts lack sequences found at the $5 sp prime$ end of the full-length transcripts of these loci and contain a common sequence, UUGUGG, which maps immediately downstream of their $5 sp prime$ termini. A similar sequence, UUGUUG, is found within orf224 downstream of the major Rfp-specific $5 sp prime$ transcript terminus; these hexanucleotide sequences may serve as recognition motifs in the generation of Mmt- and Rfp-specific transcripts. These results suggest that Rfp/Mmt is a novel nuclear locus affecting the expression of multiple mitochondrial gene regions, with different alleles or haplotypes affecting different mitochondrial genes.

Cold-acclimation-specific (CAS) gene expression was examined by screening a cDNA library prepared from poly(A)$ sp+$ RNA of cold-acclimated seedlings of a freezing-tolerant variety of alfalfa (Medicago falcata cv Anik). Three distinct CAS cDNA clones, pSM784, pSM2201, and pSM2358 were isolated. The genes corresponding to all three clones are coordinately induced by cold. Expression of these genes is not triggered by other stress treatments such as heat shock, water stress, wounding, or treatment with exogenous ABA. A positive correlation was observed between the level of expression of each gene and the degree of freezing tolerance of four alfalfa cultivars. / A full-length cDNA clone for the most abundantly-expressed gene, cas18 was isolated and sequenced. The deduced polypeptide, CAS18, is relatively small (167 amino acids), is highly hydrophillic, rich in glycine and threonine, and contains two distinctive repeat elements. It exhibits homology with members of the LEA/RAB/Dehydrin gene family--proteins which accumulate in response to water stress or abscisic acid (ABA). The cas18 cDNA hybridizes to three transcripts of 1.6, 1.4 and 1.0 kb in cold acclimated seedlings and cell cultures. The clone described here, Acs784, corresponds to the 1.0 kb transcript. / Expression of this gene is 30-fold greater in cold-acclimated cells than in nonacclimated cells after one week of low temperature treatment. Return to room temperature (deacclimation) results in the rapid disappearance of the three transcripts within just 5 hours. Studies of nuclear "run-on" transcription and transcript stability show that low temperature regulates the expression of cas18 at both the transcriptional and post-transcriptional levels.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Accompanied by zipped folders that include Excel and pdf files. Includes bibliographical references. Also available on the World Wide Web.

Thesis (MSc Natural and Agricultural Sciences (Genetics))--University of Pretoria, 2007. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Thesis (doctoral)--Helsinki University of Technology, 2008. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 78-94).