Insertional Mutants of Chlamydomonas reinhardtii That Require Elevated CO2 for Survival1

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American Society of Plant Physiologists

RESUMO

Aquatic photosynthetic organisms live in quite variable conditions of CO2 availability. To survive in limiting CO2 conditions, Chlamydomonas reinhardtii and other microalgae show adaptive changes, such as induction of a CO2-concentrating mechanism, changes in cell organization, increased photorespiratory enzyme activity, induction of periplasmic carbonic anhydrase and specific polypeptides (mitochondrial carbonic anhydrases and putative chloroplast carrier proteins), and transient down-regulation in the synthesis of Rubisco. The signal for acclimation to limiting CO2 in C. reinhardtii is unidentified, and it is not known how they sense a change of CO2 level. The limiting CO2 signals must be transduced into the changes in gene expression observed during acclimation, so mutational analyses should be helpful for investigating the signal transduction pathway for low CO2 acclimation. Eight independently isolated mutants of C. reinhardtii that require high CO2 for photoautotrophic growth were tested by complementation group analysis. These mutants are likely to be defective in some aspects of the acclimation to low CO2 because they differ from wild type in their growth and in the expression patterns of five low CO2-inducible genes (Cah1, Mca1, Mca2, Ccp1, and Ccp2). Two of the new mutants formed a single complementation group along with the previously described mutant cia-5, which appears to be defective in the signal transduction pathway for low CO2 acclimation. The other mutations represent six additional, independent complementation groups.

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