Development of a luciferase reporter gene, luxCt, for Chlamydomonas reinhardtii chloroplast

Photosystem II assembly and repair are differentially localized in Chlamydomonas

Many proteins of the photosynthesis complexes are encoded by the genome of the chloroplast and synthesized by bacterium-like ribosomes within this organelle. To determine where proteins are synthesized for the de novo assembly and repair of photosystem II (PSII) in the chloroplast of Chlamydomonas reinhardtii, we used fluorescence in situ hybridization, immunofluorescence staining, and confocal microscopy. These locations were defined as having colocalized chloroplast mRNAs encoding PSII subunits and proteins of the chloroplast translation machinery specifically under conditions of PSII subunit synthesis. The results revealed that the synthesis of the D1 subunit for the repair of photodamaged PSII complexes occurs in regions of the chloroplast with thylakoids, consistent with the current model. However, for de novo PSII assembly, PSII subunit synthesis was detected in discrete regions near the pyrenoid, termed T zones (for translation zones). In two PSII assembly mutants, unassembled D1 subunits and incompletely assembled PSII complexes localized around the pyrenoid, where we propose that they mark an intermediate compartment of PSII assembly. These results reveal a novel chloroplast compartment that houses de novo PSII biogenesis and the regulated transport of newly assembled PSII complexes to thylakoid membranes throughout the chloroplast.

The genetic transformation of plastids

Biolistic delivery of DNA initiated plastid transformation research and still is the most widelyused approach to generate transplastomic lines in both algae and higher plants. The principal designof transformation vectors is similar in both phylogenetic groups. Although important additions tothe list of species transformed in their plastomes have been made in algae and in higher plants, thekey organisms in the area are still the two species, in which stable plastid transformation was initiallysuccessful, i.e., Chlamydomonas reinhardtii and tobacco. Basicresearch into organelle biology has substantially benefited from the homologous recombination-basedcapability to precisely insert at predetermined loci, delete, disrupt, or exchange plastid genomesequences. Successful expression of recombinant proteins, including pharmaceutical proteins, hasbeen demonstrated in Chlamydomonas as well as in higher plants,where some interesting agronomic traits were also engineered through plastid transformation.

Robust expression of a bioactive mammalian protein in Chlamydomonas chloroplast

We have engineered the chloroplast of eukaryotic algae to produce a number of recombinant proteins, including human monoclonal antibodies, but, to date, have achieved expression to only 0.5% of total protein. Here, we show that, by engineering the mammalian coding region of bovine mammary-associated serum amyloid (M-SAA) as a direct replacement for the chloroplast psbA coding region, we can achieve expression of recombinant protein above 5% of total protein. Chloroplast-expressed M-SAA accumulates predominantly as a soluble protein, contains the correct amino terminal sequence and has little or no post-translational modification. M-SAA is found in mammalian colostrum and stimulates the production of mucin in the gut, acting in the prophylaxis of bacterial and viral infections. Chloroplast-expressed and purified M-SAA is able to stimulate mucin production in human gut epithelial cell lines. As Chlamydomonas reinhardtii is an edible alga, production of therapeutic proteins in this organism offers the potential for oral delivery of gut-active proteins, such as M-SAA.

Chlamydomonas reinhardtii chloroplasts as protein factories

Protein-based therapeutics are the fastest growing sector of drug development, mainly because of the high sensitivity and specificity of these molecules. Their high specificity leads to few side effects and excellent success rates in drug development. However, the inherent complexity of these molecules restricts their synthesis to living cells, making recombinant proteins expensive to produce. In addition to therapeutic uses, recombinant proteins also have a variety of industrial applications and are important research reagents. Eukaryotic algae offer the potential to produce high yields of recombinant proteins more rapidly and at much lower cost than traditional cell culture. Additionally, transgenic algae can be grown in complete containment, reducing any risk of environmental contamination. This system might also be used for the oral delivery of therapeutic proteins, as green algae are edible and do not contain endotoxins or human viral or prion contaminants.

Chlamydomonas reinhardtii: a protein expression system for pharmaceutical and biotechnological proteins

Recombinant proteins have become more and more important for the pharmaceutical and chemical industry. Although various systems for protein expression have been developed, there is an increasing demand for inexpensive methods of large-scale production. Eukaryotic algae could serve as a novel option for the manufacturing of recombinant proteins, as they can be cultivated in a cheap and easy manner and grown to high cell densities. Being a model organism, the unicellular green alga Chlamydomonas reinhardtii has been studied intensively over the last decades and offers now a complete toolset for genetic manipulation. Recently, the successful expression of several proteins with pharmaceutical relevance has been reported from the nuclear and the chloroplastic genome of this alga, demonstrating its ability for biotechnological applications.

Optimization of recombinant protein expression in the chloroplasts of green algae

Through advances in molecular and genetic techniques, protein expression in the chloroplasts of green algae has been optimized for high-level expression. Recombinant proteins expressed in algae have the potential to provide novel and safe treatment of disease and infection where current, high-cost drugs are the only option, or worse, where therapeutic drugs are not available due to their prohibitively high-cost to manufacture. Optimization of recombinant protein expression in Chlamydomonas reinhardtii chloroplasts has been accomplished by employing chloroplast codon bias and combinatorial examination of promoter and UTR combinations. In addition, as displayed by the expression of an anti-herpes antibody, the C. reinhardtii chloroplast is capable of correctly folding and assembling complex mammalian proteins. These data establish algal chloroplasts as a system for the production of complex human therapeutic proteins in soluble and active form, and at significantly reduced time and cost compared to existing production systems. Production of recombinant proteins in algal chloroplasts may enable further development of safe, efficacious and cost-effective protein therapeutics.

Circadian rhythms lit up in Chlamydomonas

Recent work on the circadian clock of the unicellular green alga Chlamydomonas reinhardtii strengthens its standing as a convenient model system for circadian study. It was shown to be amenable to molecular engineering using a luciferase-based real-time reporter for circadian rhythms. Together with the completed draft genomic sequence, the new system opens the door for genome-scale forward and reverse genetic analysis.

Real-time monitoring of chloroplast gene expression by a luciferase reporter: evidence for nuclear regulation of chloroplast circadian period

Chloroplast-encoded genes, like nucleus-encoded genes, exhibit circadian expression. How the circadian clock exerts its control over chloroplast gene expression, however, is poorly understood. To facilitate the study of chloroplast circadian gene expression, we developed a codon-optimized firefly luciferase gene for the chloroplast of Chlamydomonas reinhardtii as a real-time bioluminescence reporter and introduced it into the chloroplast genome. The bioluminescence of the reporter strain correlated well with the circadian expression pattern of the introduced gene and satisfied all three criteria for circadian rhythms. Moreover, the period of the rhythm was lengthened in per mutants, which are phototactic rhythm mutants carrying a long-period gene in their nuclear genome. These results demonstrate that chloroplast gene expression rhythm is a bona fide circadian rhythm and that the nucleus-encoded circadian oscillator determines the period length of the chloroplast rhythm. Our reporter strains can serve as a powerful tool not only for analysis of the circadian regulation mechanisms of chloroplast gene expression but also for a genetic approach to the molecular oscillator of the algal circadian clock.

Microalgae as bioreactors

Microalgae already serve as a major natural source of valuable macromolecules including carotenoids, long-chain polyunsaturated fatty acids and phycocolloids. As photoautotrophs, their simple growth requirements make these primitive plants potentially attractive bioreactor systems for the production of high-value heterologous proteins. The difficulty of producing stable transformants has meant that the field of transgenic microalgae is still in its infancy. Nonetheless, several species can now be routinely transformed and algal biotechnology companies have begun to explore the possibilities of synthesizing recombinant therapeutic proteins in microalgae and the engineering of metabolic pathways to produce increased levels of desirable compounds. In this review, we compare the current commercially viable bioreactor systems, outline recent progress in microalgal biotechnology and transformation, and discuss the potential of microalgae as bioreactors for the production of heterologous proteins.

Contribution of 5'- and 3'-untranslated regions of plastid mRNAs to the expression of Chlamydomonas reinhardtii chloroplast genes

Expression of chloroplast genes is primarily regulated posttranscriptionally, and a number of RNA elements, found in either the 5'- or 3'-untranslated regions (UTRs) of plastid mRNAs, that impact gene expression have been identified. Complex regulatory and feedback mechanisms influence both translation and protein accumulation, making assignment of roles for specific RNA elements difficult. To identify specific contributions made by various UTRs on translation of plastid mRNAs, we used a heterologous gfp reporter gene that is fused combinatorially to chloroplast 5'- and 3'-UTRs. In general, the 5'-UTR, including the promoter, of the plastid atpA and psbD genes produced the highest levels of chimeric mRNA and protein accumulation, while the 5'-UTR of the rbcL and psbA genes produced less mRNA and protein. Varying the 3'-UTR had little impact on mRNA and protein accumulation, as long as a 3'-UTR was present. Overall, accumulation of chimeric mRNAs was proportional to protein accumulation, with a few notable exceptions. Light-regulated translation continues to operate in chimeric mRNAs containing the 5'-UTR of either the psbA or psbD mRNAs, despite translation of these two chimeric mRNAs at very different efficiencies, suggesting that translational efficiency and light-regulated translation are separate events. Translation of some chimeric mRNAs was much more efficient than others, suggesting that interactions between the untranslated and coding sequences can dramatically impact translational efficiency.

Recent developments in the production of human therapeutic proteins in eukaryotic algae

Antibody-based therapeutics have had great success over the last few years, and continue to be one of the fastest growing sectors of drug development. The efficacy and specificity of antibody-based drugs makes them ideal candidates for new drug development, but the specificity of these drugs comes from their complexity, and this complexity makes antibodies very expensive to produce. To address this problem, the authors have developed a system for the expression of recombinant proteins using the unicellular eukaryotic green algae, Chlamydomonas reinhardtii. As proof of concept, the authors have engineered microalgae to produce several forms of a human IgA antibody directed against herpes simplex virus. The expression of human monoclonal antibodies in C. reinhardtii offers an attractive alternative to traditional mammalian-based expression systems, as both the plastid and nuclear genomes are easily and quickly transformed, and the production of proteins in algae has an inherently low cost of capitalisation and production.

Expression of human antibodies in eukaryotic micro-algae

Protein based therapeutics have enjoyed great success over the past decade. Unfortunately, with this clinical success comes a heavy price tag, owing to the inherently high costs of capitalization and production using mammalian cell fermentation. To address this problem, we have begun developing a system for the expression of recombinant proteins in the unicellular eukaryotic green algae, Chlamydomonas reinhardtii, leading to the production of human IgA single chain antibodies. The expression of human monoclonal antibodies in C. reinhardtii offers an attractive alternative to traditional mammalian based expression systems for several reasons, including an ability to rapidly obtain stable plastid and nuclear transformants, coupled with inherently low costs of capitalization and production.

BIOLUMBASE?the database of natural and transgenic bioluminescent organisms

The Institute of Biophysics SB RAS hosts and maintains a specialized collection of luminous bacteria (CCIBSO 836) containing over 700 strains isolated in various regions of the world's oceans. The culture collection is a source of lux genes and biologically active substances. The wide application of bioluminescence in medicine and ecology has given importance to analysing information on the structure and functioning of bioluminescence systems in natural and transgenic microorganisms, as well as on their features that are closely interrelated with bioluminescence. The aims of our BIOLUMBASE database are: gathering information on microorganisms with lux genes, their analysis and free access, and distribution of this data throughout the global network. The database includes two sections, natural and transgenic luminous microorganisms, and is updated by our own experimental results, the published literature and internet resources. For the future, a publicly available internet site for BIOLUMBASE is planned. This will list the strains and provide comprehensive information on the properties and functions of luminous bacteria, the mechanisms of regulation of bioluminescence systems, constructs with lux genes, and applications of bioluminescence in microbiology, ecology, medicine and biotechnology. It is noteworthy that this database will also be useful for evaluation of biological hazards of transgenic strains. Users will be able to carry out bibliographic and strain searches starting from any feature of interest.

Monitoring dynamic expression of nuclear genes in Chlamydomonas reinhardtii by using a synthetic luciferase reporter gene

For monitoring the expression profile of selected nuclear genes in Chlamydomonas reinhardtii in response to altered environmental parameters or during cell cycle, in the past many RNA or protein samples had to be taken and analyzed by RNA hybridization or protein immunoblotting. Here we report the synthesis of a gene that codes for the luciferase of Renilla reniformis (RLuc) and is adapted to the nuclear codon usage of C. reinhardtii . This crluc gene was expressed alone or as a fusion to the zeocin resistance gene ble under control of different promoter variants. Luciferase activity was monitored in living cells, increased with the promoter strength and paralleled the amount of expressed protein. Under control of the Lhcb-1 promoter the Luc-activity in synchronized cultures was dependent on the dark-light cycle. Additionally, crluc was placed under control of the Chop-2 promoter and activity was measured under different light conditions. Chop-2 promoter activity was found to be most pronouced under low-light and dark conditions, further supporting that channelrhodopsin-2 is most active in dark-adapted cells. We conclude that crluc is a reliable tool for convenient monitoring of nuclear gene expression in C. reinhardtii .

Prospects for molecular farming in the green alga Chlamydomonas

Protein-based therapeutics have enjoyed great success over the past decade. Unfortunately, this clinical success has come with a heavy price tag that is due to the inherently high costs of the capitalization and production of these complex molecules using current mammalian-based fermentation systems. Recent progress has been made in the production of recombinant proteins, including antibodies, in the eukaryotic unicellular green alga Chlamydomonas reinhardtii. C. reinhardtii offers an attractive alternative to traditional mammalian-based expression systems for several reasons, including its ability to provide stable plastid and nuclear transformants rapidly and its inherently low costs for capitalization and production.