Dataset Information

Elevated Inorganic Carbon Concentrating Mechanism Confers Tolerance to High Light in an Arctic Chlorella sp. ArM0029B.

ABSTRACT: Microalgae and higher plants employ an inorganic carbon (Ci) concentrating mechanism (CCM) to increase CO2 availability to Rubisco. Operation of the CCM should enhance the activity of the Calvin cycle, which could act as an electron sink for electrons generated by photosynthesis, and lower the redox status of photosynthetic electron transport chains. In this study, a hypothesis that microalgal cells with fully operating CCM are less likely to be photodamaged was tested by comparing a Chlorella mutant with its wild type (WT). The mutant acquired by screening gamma-ray-induced mutant libraries of Chlorella sp. ArM0029B exhibited constitutively active CCM (CAC) even in the presence of additional Ci sources under mixotrophic growth conditions. In comparison to the WT alga, the mutant named to constitutively active CCM1 (CAC1) showed more transcript levels for genes coding proteins related to CCM such as Ci transporters and carbonic anhydrases (CA), and greater levels of intracellular Ci content and CA activity regardless of whether growth is limited by light or not. Under photoinhibitory conditions, CAC1 mutant showed faster growth than WT cells with more PSII reaction center core component D1 protein (encoded by psbA), higher photochemical efficiency as estimated by the chlorophyll fluorescence parameter (Fv/Fm), and fewer reactive oxygen species (ROS). Interestingly, high light (HL)-induced increase in ROS contents in WT cells was significantly inhibited by bicarbonate supplementation. It is concluded that constitutive operation of CCM endows Chlorella cells with resistance to HL partly by reducing the endogenous generation of ROS. These results will provide useful information on the interaction between CCM expression, ROS production, and photodamage in Chlorella and related microalgae.

SUBMITTER: Hwangbo K

PROVIDER: S-EPMC5949578 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Elevated Inorganic Carbon Concentrating Mechanism Confers Tolerance to High Light in an Arctic <i>Chlorella</i> sp. ArM0029B.

Hwangbo Kwon K Lim Jong-Min JM Jeong Seok-Won SW Vikramathithan Jayaraman J Park Youn-Il YI Jeong Won-Joong WJ

Frontiers in plant science 20180507

Microalgae and higher plants employ an inorganic carbon (Ci) concentrating mechanism (CCM) to increase CO<sub>2</sub> availability to Rubisco. Operation of the CCM should enhance the activity of the Calvin cycle, which could act as an electron sink for electrons generated by photosynthesis, and lower the redox status of photosynthetic electron transport chains. In this study, a hypothesis that microalgal cells with fully operating CCM are less likely to be photodamaged was tested by comparing a ...[more]

PMID: 29868055

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Project description:BACKGROUND: Chorella is the representative taxon of Chlorellales in Trebouxiophyceae, and its chloroplast (cp) genomic information has been thought to depend only on studies concerning Chlorella vulgaris and GenBank information of C. variablis. Mitochondrial (mt) genomic information regarding Chlorella is currently unavailable. To elucidate the evolution of organelle genomes and genetic information of Chlorella, we have sequenced and characterized the cp and mt genomes of Arctic Chlorella sp. ArM0029B. RESULTS: The 119,989-bp cp genome lacking inverted repeats and 65,049-bp mt genome were sequenced. The ArM0029B cp genome contains 114 conserved genes, including 32 tRNA genes, 3 rRNA genes, and 79 genes encoding proteins. Chlorella cp genomes are highly rearranged except for a Chlorella-specific six-gene cluster, and the ArM0029B plastid resembles that of Chlorella variabilis except for a 15-kb gene cluster inversion. In the mt genome, 62 conserved genes, including 27 tRNA genes, 3 rRNA genes, and 32 genes encoding proteins were determined. The mt genome of ArM0029B is similar to that of the non-photosynthetic species Prototheca and Heicosporidium. The ArM0029B mt genome contains a group I intron, with an ORF containing two LAGLIDADG motifs, in cox1. The intronic ORF is shared by C. vulgaris and Prototheca. The phylogeny of the plastid genome reveals that ArM0029B showed a close relationship of Chlorella to Parachlorella and Oocystis within Chlorellales. The distribution of the cox1 intron at 721 support membership in the order Chlorellales. Mitochondrial phylogenomic analyses, however, indicated that ArM0029B shows a greater affinity to MX-AZ01 and Coccomyxa than to the Helicosporidium-Prototheca clade, although the detailed phylogenetic relationships among the three taxa remain to be resolved. CONCLUSIONS: The plastid genome of ArM0029B is similar to that of C. variabilis. The mt sequence of ArM0029B is the first genome to be reported for Chlorella. Chloroplast genome phylogeny supports monophyly of the seven investigated members of Chlorellales. The presence of the cox1 intron at 721 in all four investigated Chlorellales taxa indicates that the cox1 intron had been introduced in early Chorellales as a cis-splice form and that the cis-splicing intron was inherited to recent Chlorellales and was recently trans-spliced in Helicosporidium.

Project description:Synechocystis 6803 cells was grown photoautotrophically at 32 °C buffered in BG-11 and bubbled with 3% CO2. A relatively mild Ci stress was applied by switching the aeration from 3% CO2 to air alone. After incubation under designated conditions, a 100-ml aliquot of culture was immediately combined with an equal volume of ice-cold mixture of phenol and ethanol (1:10, w/v) in an ice bath. The resultant cells were collected by centrifugation at 1000 x g for 10 min at 4 °C. Total RNA was isolated with RNeasy Midi Kit (Qiagen, Valencia, CA) and further treated with the DNA-free kit (Ambion, Austin, TX). Fluorescently labeled cDNA was produced via a two-step indirect procedure involving cDNA synthesis from 16 µg of total RNA in a reverse transcriptase reaction incorporating aminoallyl-modified deoxynucleotide, followed by the second step involving chemical coupling of fluorescent dye to the introduced amino moieties of the synthesized cDNA. Labeled cDNA were adjusted to 14.75 µl, and the remainder of the hybridization components containing 2.5 µl of 10 µg µl-1 salmon sperm DNA, 8.75 µl of 20x SSC, 0.25 µl of 10% SDS, and 8.75 µl of formamide were added. The mixture was then heated for 2 min at 99 °C and maintained at 42 °C until hybridization. Hybridizations were preformed in a static incubator at 42 °C for 12-16 h then washed by placing in a 250-ml solution of 2x SSC and 0.1% SDS at 42 °C for 5 min with gentle agitation provided by rotation of a magnetic stir bar. The slide was transferred quickly to a 250-ml solution of 0.1x SSC and 0.1% SDS, incubated for 10 min at room temperature with gentle agitation, and washed five additional times in 0.1x SSC for 1 min at room temperature. Hybridization signals from the microarray were quantified using GenePix Pro 4.1 (Axon Instruments, Union City, CA). The quality control procedures were conducted in the image analysis software, and then data were saved to Acuity 3.1 (Axon Instruments). Keywords: time-course

Dataset Information

Elevated Inorganic Carbon Concentrating Mechanism Confers Tolerance to High Light in an Arctic Chlorella sp. ArM0029B.

Publications

Elevated Inorganic Carbon Concentrating Mechanism Confers Tolerance to High Light in an Arctic <i>Chlorella</i> sp. ArM0029B.

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