The Regulation of Carbonic Anhydrase and Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Activase by Light and CO2 in Chlamydomonas reinhardtii

Abstract

We have investigated the regulation of accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase activase and the periplasmic carbonic anhydrase (CA) in Chlamydomonas reinhardtii. In algae, the periplasmic CA is required for efficient CO, fixation when the CO, concentration is low. These two proteins are affected differently by the CO, level in the environment. The steady-state level of the ribulose-l,5-bisphosphate carboxylase/oxygenase activase transcript was only slightly and transiently affected by a reduction in ambient CO, concentration, whereas the CA transcript level was strongly induced by air containing ambient (350 parts per million) CO, (low CO,) conditions. The transcripts for both proteins showed strong oscillations when the alga was grown under a 12-h light/l2-h dark growth regime, with the transcripts encoding these proteins present just before the onset of the light cycle. l h e observation that the CA transcript was made in the dark was surprising, since earlier reports indicated that active photosynthesis was required for the induction of the periplasmic CA. Further experiments demonstrated that the CA transcript was partially induced under low-CO, conditions even when the switch to low CO, was done in the dark. Our results suggest that C. reinhardtiimight sense the CO, concentration in a more direct manner than through C, or C, cycle intermediates, which has been previously suggested.In higher plants, a number of proteins are required for growth on low CO,. These proteins include Rubisco activase, the enzymes of the C, or photorespiratory cycle, and enzymes involved in nitrogen assimilation. In addition to these proteins, unicellular algae also have a C0,-concentrating mechanism that overcomes the slow diffusion of CO, in the aqueous environment under low-CO, conditions. The C0,-concentrating mechanism in Chlamydomonas reinhardtii is influenced by the level of CO, in the environment (Badger et al., 1980; Aizawa and Miyachi, 1986). C. reinhardtii cells that are grown under high-CO, conditions have an apparent affinity for CO, similar to that of C, plants, requiring about 20 to 30 ~L M CO, for maximal rates of photosynthesis. However, when alga1 cells are placed in low CO,, their apparent affinity for CO, increases and only 1 to 2 ~L M CO, is required for high rates of photosynthesis. The induction of the C0,-concentrating mechanism results in the synthesis of at least six proteins (Coleman et al.,

Dynamics of Carbon-Concentrating Mechanism Induction and Protein Relocalization during the Dark-to-Light Transition in Synchronized Chlamydomonas reinhardtii

“…This indicates that LCR1 and CAH1 transcription may be regulated in a different manner to other CO 2 -responsive genes. Rawat and Moroney (1995) also identified strong oscillations of CAH1 transcripts in synchronized cells, and CAH1 was later shown to be under circadian control (Fujiwara et al, 1996). The higher abundance of CAH1 mRNA in -2D (dark/light) cells compared with 0-h (CO 2 ) cells is consistent with the previous observation of the presence of CAH1 mRNA in cells at the end of the dark period (Supplemental Table S1; Rawat and Moroney, 1995).…”

Characterization of carbonic anhydrase from diversified genus for biomimetic carbon-dioxide sequestration

“…5). Similar results have been reported for α-CA in H. pylori, R. palustris and C. reinhardtii [26,28,29]. On the basis of more than 80% inhibition with sulphanilamide and a molecular weight in the region of ~29 kDa, it can be predicted that the CA from all the four isolates evaluated during the present study is of α-type, however confi rmation has to be done through immunoblotting.…”

“…Similar results have been reported in H. pylori and bacteria from the karst areas [26,27], whereas only the periplasmic fraction revealed a signifi cant activity in A. hydrophila (1.56 EU/ml) and A. caviae (1.57 EU/ml). Similar results [25,28,29]. Periplasmic location of the enzyme is signifi cant in maintenance and regulation of pH and ionic concentration.…”

Lack of the Rhesus protein Rh1 impairs growth of the green alga Chlamydomonas reinhardtii at high CO 2

“…2A). Expression of the periplasmic carbonic anhydrase gene CAH1, which is known to be induced only under conditions of limiting carbon availability (35)(36)(37), was detected in all strains grown in air but not in high CO 2 (Fig. 2B).…”