Transcriptional regulatory network of genes for carbon concentrating mechanisms

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Chlamydomonas reinhardtii can acclimate to environmental stresses such as low CO_2-supply, high-light by inducing a set of genes for a carbon-concentrating mechanism (CCM) through putative signal transduction pathways. Expression of several CCM-related genes, Cahl coding for a periplasmic carbonic anhydrase (CA), Mca for a mitochondrial CA and Ccpl for a chloroplast envelope protein LIP-36, is induced by lowering CO_2. This acclimation to CO_2-limiting conditions suggests the existence of sensory mechanisms by which cells perceive the shortage of CO_2 and pathways by which the signal is transduced into the specific gene regulation. We have cloned a nuclear regulatory gene, Ccml, which complements the mutation in the pleiotropic high-CO_2 requiring mutant C16 (Fukuzawa et.al. 2001). Ccml is constitutively expressed both in high- and low-CO_2 conditions. His-54 in the zinc-finger motif of CCM1 is essential to its regulatory function. To isolate target genes, which are controlled by CCM1, we have developed cDNA macroarray containing 10,368 EST (Fukuzawa et al.). RNA samples from WT cells cultured in high-CO_2 or low-CO_2 and also from the low-CO_2-acclimated C16 were labeled with ^<33>P-dCTP and hybridized with cDNA array membranes. Fifty-nine low-CO_2 inducible EST clones were not induced in the C16 mutant, suggesting that these are regulated by CCM1l. Time-dependent expression patterns of EST clones enabled us to detect low-CO_2 inducible (Lci) genes containing those for photorespiration or ion-transporters. Relationship between CO_2-limiting stress and photorespiration or high-light stress will be discussed as well as CO_2-signal transduction pathways deduced from array analyses of regulatory mutants.