| Photosynthetic microorganisms must acclimate to environmental conditions that may lead to photo-oxidative stress, such as low CO2 environments or high light intensities. Chlamydomonas reinhardtii, a unicellular, green alga with a Carbon Concentrating Mechanism (CCM), effectively accumulates inorganic carbon (Ci) to levels higher than external concentrations. The CCM concentrates inorganic carbon around Rubisco to increase the CO 2 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 BleR cassette, selected for Zeocin resistance, and then screened for a "sick on low CO 2" 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 BleR insert in the first exon of Hdh1, a novel, single copy gene that seems to be slightly upregulated under low CO2 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 K0.5), a decreasing photosynthetic rate (Vmax) over time, and a lower content of chlorophylls and quenching xanthophylls than wild-type. Some possible roles of Hdh1 are discussed. |
