CO2-Responsive Transcriptional Regulation ofCAH1 Encoding Carbonic Anhydrase Is Mediated by Enhancer and Silencer Regions in Chlamydomonas reinhardtii  

Abstract

Chlamydomonas reinhardtii adapts to the stress of CO 2 -limiting conditions through the induction of a set of genes including CAH1, which encodes a periplasmic carbonic anhydrase. CAH1 is upregulated under low-CO 2 conditions (air containing 0.04% [v/v] CO 2 ) in the presence of light, whereas it is down-regulated under high-CO 2 conditions (5% [v/v] CO 2 ) or in the dark. In an effort to identify cis-elements involved in the transcriptional regulation of CAH1, a series of 5-nested deletions of the region upstream of CAH1 were fused to a promoterless arylsulfatase reporter gene (ARS). The upstream region from ؊651 to ؉41 relative to the transcription start site was sufficient to regulate the expression of ARS with kinetics similar to those of endogenous CAH1. Deletion of the region between ؊651 and ؊294 resulted in a significant decrease in the level of arylsulfatase activity expressed under low-CO 2 conditions. The 543-bp upstream region from ؊651 to ؊109, without any promoter elements, CAAT-box, or TATA-box, could confer CO 2 and light responsiveness on the ␤ 2 -tubulin minimal promoter. This 543-bp region was divided into two parts: a 358-bp silencer region from ؊651 to ؊294, which represses the minimal promoter activity under high-CO 2 conditions, and a 185-bp enhancer region from ؊293 to ؊109, which activates the promoter under low-CO 2 conditions in the presence of light.

CO2 Sensing at Ocean Surface Mediated by cAMP in a Marine Diatom

“…However, the light signaling pathway in CCM regulation has not been elucidated in detail. In the marine diatom P. tricornutum, the ptca1 gene is repressed in the dark to about 40% of that under illumination , but the promoter sequence of ptca1 is not similar to any of known CO 2 -responsive promoters (Villand et al, 1997;Kucho et al, 1999;. This indicates that the origins of CO 2 -response systems are also diverse.…”

“…Responses of CCM components to light in eukaryotic algae are also diverse, but the absence of light is strongly or moderately repressive in many algal species (Matsuda and Colman, 1995;Villand et al, 1997;Kucho et al, 1999;. However, the light signaling pathway in CCM regulation has not been elucidated in detail.…”

“…significant levels of CCM expression occurred in the dark in air; Matsuda and Colman, 1995;. In C. reinhardtii, regulation of the CO 2 -responsive gene Cah1 was shown to be regulated by both silencer and enhancer in its promoter region in response to changing the ambient [CO 2 ], and the absence of light constitutes a repressive signal to the Cah1 promoter via the silencer region (Kucho et al, 1999). These observations strongly suggest the occurrence of cross talk between light and CO 2 signals in CCM regulation.…”

“…CO 2 -sensing mechanisms, as described above, have been studied in a limited number of algae, primarily freshwater and soil species (Matsuda and Colman, 1995;Rawat and Moroney, 1995;Badger et al, 1998;Eriksson et al, 1998;Kaplan and Reinhold, 1999;Kucho et al, 1999;Miura et al, 2004;Vance and Spalding, 2005;Woodger et al, 2005), but little molecular information is available on marine eukaryotic algae. CO 2 is a redundant molecule that influences a variety of physiological processes in microbes, plants, and animals, and, as a precedent, the initial process of sensing [CO 2 ] has been found in a mammalian tissue.…”

Cis-acting Elements and DNA-Binding Proteins Involved in CO2-Responsive Transcriptional Activation of Cah1 Encoding a Periplasmic Carbonic Anhydrase in Chlamydomonas reinhardtii

“…This activation does not occur when cells are cultured in the dark or in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, suggesting that photosynthetic electron flow is required . By using a reporter gene encoding arylsulfatase (Ars) driven by the ␤ 2 -tubulin minimal promoter, transcription of Cah1 has been shown to be controlled by two regulatory regions: a silencer region, which represses the transcription under high-CO 2 conditions or in the dark, and an enhancer region, which activates it under low-CO 2 conditions in light (Kucho et al, 1999). However, the detailed nucleotide sequences of cis-acting elements and presence of DNAbinding proteins related to Cah1 regulation have not been identified.…”