Oldenburg, Delene J. , Rowan, Beth A. , Shaver, Jeffrey M. , Bendich, Arnold J. .
Chloroplast DNA: structure, replication, and light-regulation.
We have developed a model for the plastid chromosome incorporating information about chloroplast DNA (cpDNA) structure, replication and light regulation during plastid development. We address two aspects of plastid biology. 1) Although the circular concept for the plastome has persisted for 30 years, recent data indicate linear and branched multigenomic molecules. Thus, it is time to replace the circular concept with a model more accurately reflecting the data. 2) In proplastid-to-chloroplast development, a sharp increase in cpDNA occurs, followed by a rapid decline, but little is known of the mechanisms regulating cpDNA levels. We investigated the effects of light on cpDNA during development using maize, Arabidopsis, and Medicago truncatula. We find no obvious structural difference in cpDNA between plastomes with (maize) and without (M. truncatula) an inverted repeat (IR) sequence. For both plants, restriction mapping reveals fragments diagnostic of linear molecules with defined ends and putative origins of replication near the ends, with some origins common among species. We propose a recombination-dependent mechanism of replication that is the same for both IR and non-IR plastomes. As plastids develop in light-grown plants, cpDNA levels decline, paralleled by a decrease in size and complexity of the DNA molecules, but the extent of cpDNA loss varies among species. In the dark, cpDNA levels are high and decline rapidly upon transfer to light for maize, whereas for M. truncatula cpDNA is low in the dark, initially increases then decreases in the light. We propose that the light signal transduction system governing photomorphogenesis is also involved in maintaining cpDNA, based, in part, on experiments employing red light in maize and phyB and cop1 mutants in Arabidopsis.
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1 - Unversity of Washington, Department of Biology, Box 355325, Seattle, Washington, 98195-5325, United States of America
2 - University of Washington, Department of Biology
Presentation Type: Oral Paper:Papers for Topics
Location: Boulevard B/Hilton
Date: Wednesday, July 11th, 2007
Time: 2:45 PM