Date of Award
Doctor of Philosophy
Martin H. Spalding
The regulation of genes by CO[subscript]2 concentration in wild type and mutants of the unicellular green alga Chlamydomonas reinhardtii was studied. This and other algal species can photosynthesize efficiently under limiting concentrations of CO[subscript]2 due to the activities of a CO[subscript]2 concentrating mechanism and carbonic anhydrase. A cDNA copy of the gene that codes for a periplasmic carbonic anhydrase (perCA) was isolated and used to study regulation of perCA synthesis in a cell wall-deficient mutant (CW-15). Over-expression of perCA in CW-15, relative to wild type, was found at the levels of enzyme activity, protein content, and mRNA abunDance; This regulation may be attributed to the inability of the mutant to retain perCA protein in the periplasmic space owing to the absence of an intact cell wall. Further, these findings suggest the cells can perceive and control (at the level of transcript abundance) perCA protein content;Another mutant, CIA-5, which lacks all components known to be required for CO[subscript]2 accumulation, was found to not accumulate perCA transcripts in response to limiting CO[subscript]2. In addition, transcript for the cabII-1 gene, which codes for one of the light harvesting chlorophyll binding proteins of photosystem II, was found to increase in abundance in response to limiting CO[subscript]2 in wild type cells but not in the CIA-5 mutant;Finally, the control by CO[subscript]2 concentration over synthesis of the large (L) and small (S) subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase was investigated. In vivo protein labeling experiments indicated that both subunits were made at lower rates (or were more rapidly turned-over) in cells exposed to limiting CO[subscript]2 for 4 to 8 hours than in 24 hour-limiting CO[subscript]2-adapted cells or in cells cultured under elevated CO[subscript]2. Involvement of adjustment in mRNA pool size in contributing to this response was ruled-out. Using in vivo pulse-chase protein labelings it was determined that, in cells exposed to limiting CO[subscript]2 for 4 hours, translation of L and S transcripts was arrested.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Thomas Leslie Winder
Winder, Thomas Leslie, "Changes in gene expression during induction of the carbon dioxide concentrating mechanism in Chlamydomonas reinhardtii " (1991). Retrospective Theses and Dissertations. 9622.