The Novel Myb Transcription Factor LCR1 Regulates the CO2-Responsive Gene Cah1, Encoding a Periplasmic Carbonic Anhydrase in Chlamydomonas reinhardtii  [W]

Abstract

Chlamydomonas reinhardtii acclimates to CO 2 -limiting stress by inducing a set of genes for a carbon-concentrating mechanism (CCM). This set includes the gene Cah1, which encodes a periplasmic carbonic anhydrase. Although physiological aspects of CO 2 response have been extensively studied, regulatory components, such as transcription factors involved in the acclimation, have not been well described in eukaryotic microalgae. Using an arylsulfatase gene driven by the Cah1 promoter, a regulatory mutant of Cah1 was isolated and named lcr1 (for low-CO 2 stress response). The photosynthetic affinity for inorganic carbon of lcr1 was reduced compared with that of wild-type cells. Expression of three low-CO 2 -inducible genes, Cah1, Lci1, and Lci6, were regulated by LCR1 as shown by cDNA array and RNA gel blot analyses. The Lcr1 gene encodes a protein of 602 amino acids containing a single Myb domain, which binds to the Cah1-promoter region. Expression of Lcr1 was induced by lowering CO 2 levels and controlled by the regulatory factor CCM1. These results suggest that LCR1 transmits the low CO 2 signal to at least three CO 2 -responsive genes and then fully induces CCM.

Expression of a Low CO2–Inducible Protein, LCI1, Increases Inorganic Carbon Uptake in the Green Alga Chlamydomonas reinhardtii

“…After transformation of the chimeric plasmid into the lcr1 mutant, Zeocin-resistant colonies were selected and used for RNA gel blot analyses with a probe specific to the LCI1 coding region ( Figure 3B). The level of endogenous LCI1 mRNAs of 1.3 kb (Burow et al, 1996;Yoshioka et al, 2004) increased in LC-grown Q304P3. In the lcr1 mutant, there was no significant accumulation of the LCI1 mRNA either under LC conditions or in the presence of NO 3 2 , although this mutant previously was shown to accumulate a trace amount of LCI1 mRNA under LC conditions .…”

“…In addition, the lcr1 mutant showed a 30% decrease in growth rate and a higher apparent K 1/2 (Ci) value compared with that of photosynthetically wild-type strain Q304P3 under LC conditions. Because it has been shown that a loss of CAH1 does not result in reduced growth under LC conditions (Van and Spalding, 1999) and that LCI6 encodes a soluble protein , the putative membrane protein LCI1 was assumed to play a significant role in the CCM (Burow et al, 1996;Yoshioka et al, 2004).…”

Visualization of Nuclear Localization of Transcription Factors with Cyan and Green Fluorescent Proteins in the Red Alga Porphyra yezoensis

“…In land plants and green algae, the important role of transcription factors during stress responses and development has been demonstrated. For example, CBF1, 2 and 3 direct cold-inducible gene expression in Arabidopsis thaliana (Chinnusamy et al 2007), while Myb transcription factor LCR1 regulates the CO 2 responsive gene Cah1 under CO 2 limiting stress in Chlamydomonas reinhardtii (Yoshioka et al 2004). Moreover, in Volvox carteri, RegA plays a central role as a master regulatory gene in germ-soma differentiation by suppression of reproductive activities in somatic cells (Babinger et al 2006).…”

Light and CO2/cAMP Signal Cross Talk on the Promoter Elements of Chloroplastic β-Carbonic Anhydrase Genes in the Marine Diatom Phaeodactylum tricornutum

“…The Cah1 promoter is regulated positively and negatively by enhancer and silencer regions. The enhancer region is controlled by two critical elements denoted enhancer-element consensus (Kucho et al, 2003), to which a class of basic-ZIP transcription factors, enhancer-element-consensus binding proteins, interact (Yoshioka et al, 2004). A zinc finger protein, CCM1/Cia5, has been found to be involved in the up-regulation of most low-CO 2 -inducible genes, strongly suggesting that CCM1/Cia5 is a master regulator for the transcriptional response of the Chlamydomonas CCM, but the mechanism of the initial CO 2 signal perception is still unknown (Fukuzawa et al, 2001;Xiang et al, 2001).…”