Photosynthetic microorganisms must acclimate to environmental conditions that may lead to photo-oxidative stress, such as low CO<sub>2</sub> environments or high light intensities. Chlamydomonas reinhardtii, a unicellular, green alga with a Carbon Concentrating Mechanism (CCM), effectively accumulates inorganic carbon (C<sub>i</sub>) to levels higher than external concentrations. The CCM concentrates inorganic carbon around Rubisco to increase the CO<sub>2</sub> fixation efficiency of C. reinhardtii. Photorespiration, the water-water cycle, the xanthophyll cycle, and the CCM are adaptations that also prevent the over-reduction of photosystems and thus photoinhibition by dissipating the energy from the absorption of excess photons. In an effort to dissect elements of the CCM, insertional mutants of C. reinhardtii were transformed using the Ble<sup>R</sup> cassette, selected for Zeocin resistance, and then screened for a "sick on low CO<sub>2</sub>" phenotype. One insertional mutant selected was slc-230. This dissertation describes the molecular and the physiological characterization of slc-230.
slc-230 was shown to have a Ble<sup>R</sup> insert in the first exon of Hdh1, a novel, single copy gene that seems to be slightly upregulated under low CO<sub>2</sub> and whose predicted gene product has homology with open reading frames in archaebacteria. The Hdh1 gene product has similarity to general phosphatases. Proteins in this family include phosphatases and epoxide hydrolases. In addition, Hdh1 is predicted to be localized to the chloroplast or mitochondria in C. reinhardtii. It was found that a genomic copy of Hdh1 can complement slc-230.
Physiological studies were conducted to determine the effects of the altered expression of Hdh1 in slc-230. slc-230 exhibits a lower affinity for inorganic carbon (slightly elevated K<sub>0.5</sub>), a decreasing photosynthetic rate (V<sub>max</sub>) over time, and a lower content of chlorophylls and quenching xanthophylls than wild-type. Some possible roles of Hdh1 are discussed.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-04092004-115604 |
| Date | 12 April 2004 |
| Creators | Adams, James Edward,IV |
| Contributors | Sue G. Bartlett, Charles Overstreet, James V. Moroney, John C. Larkin, Thomas S. Moore |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-04092004-115604/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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