Dataset Information

A cytochrome b5-containing plastid-located fatty acid desaturase from Chlamydomonas reinhardtii.

ABSTRACT: Monogalactosyldiacylglycerol (MGDG) in Chlamydomonas reinhardtii and other green algae contains hexadeca-4,7,10,13-tetraenoic acid (16:4) in the glycerol sn-2 position. While many genes necessary for the introduction of acyl chain double bonds have been functionally characterized, the ?4-desaturase remained unknown. Using a phylogenetic comparison, a candidate gene encoding the MGDG-specific ?4-desaturase from Chlamydomonas (Cr?4FAD) was identified. Cr?4FAD shows all characteristic features of a membrane-bound desaturase, including three histidine boxes and a transit peptide for chloroplast targeting. But it also has an N-terminal cytochrome b(5) domain, distinguishing it from other known plastid desaturases. Cytochrome b(5) is the primary electron donor for endoplasmic reticulum (ER) desaturases and is often fused to the desaturase domain in desaturases modifying the carboxyl end of the acyl group. Difference absorbance spectra of the recombinant cytochrome b(5) domain of Cr?4FAD showed that it is functional in vitro. Green fluorescent protein fusions of Cr?4FAD localized to the plastid envelope in Chlamydomonas. Interestingly, overproduction of Cr?4FAD in Chlamydomonas not only increased levels of 16:4 acyl groups in cell extracts but specifically increased the total amount of MGDG. Vice versa, the amount of MGDG was lowered in lines with reduced levels of Cr?4FAD. These data suggest a link between MGDG molecular species composition and galactolipid abundance in the alga, as well as a specific function for this fatty acid in MGDG.

SUBMITTER: Zauner S

PROVIDER: S-EPMC3416504 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature

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A cytochrome b5-containing plastid-located fatty acid desaturase from Chlamydomonas reinhardtii.

Zäuner Simone S Jochum Wibke W Bigorowski Tara T Benning Christoph C

Eukaryotic cell 20120504 7

Monogalactosyldiacylglycerol (MGDG) in Chlamydomonas reinhardtii and other green algae contains hexadeca-4,7,10,13-tetraenoic acid (16:4) in the glycerol sn-2 position. While many genes necessary for the introduction of acyl chain double bonds have been functionally characterized, the Δ4-desaturase remained unknown. Using a phylogenetic comparison, a candidate gene encoding the MGDG-specific Δ4-desaturase from Chlamydomonas (CrΔ4FAD) was identified. CrΔ4FAD shows all characteristic features of a ...[more]

PMID: 22562471

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Project description:BACKGROUND: The mutational-hazard hypothesis argues that the noncoding-DNA content of a genome is a consequence of the mutation rate (mu) and the effective number of genes per locus in the population (N(g)). The hypothesis predicts that genomes with a high N(g)mu will be more compact than those with a small N(g)mu. Approximations of N(g)mu can be gained by measuring the nucleotide diversity at silent sites (pi(silent)). We addressed the mutation-hazard hypothesis apropos plastid-genome evolution by measuring pi(silent) of the Chlamydomonas reinhardtii plastid DNA (ptDNA), the most noncoding-DNA-dense plastid genome observed to date. The data presented here in conjunction with previously published values of pi(silent) for the C. reinhardtii mitochondrial and nuclear genomes, which are respectively compact and bloated, allow for a complete analysis of nucleotide diversity and genome compactness in all three genetic compartments of this model organism. RESULTS: In C. reinhardtii, the mean estimate of pi(silent) for the ptDNA (14.5 x 10(-3)) is less than that of the nuclear DNA (32 x 10(-3)) and greater than that of the mitochondrial DNA (8.5 x 10(-3)). On average, C. reinhardtii has approximately 4 times more silent-site ptDNA diversity than the mean value reported for land plants, which have more compact plastid genomes. The silent-site nucleotide diversity of the different ptDNA loci that were studied varied significantly: from 0 to 71 x 10(-3) for synonymous sites and from 0 to 42 x 10(-3) for intergenic regions. CONCLUSION: Our findings on silent-site ptDNA diversity are inconsistent with what would be expected under the mutational-hazard hypothesis and go against the documented trend in other systems of pi(silent) positively correlating with genome compactness. Overall, we highlight the lack of reliable nucleotide-diversity measurements for ptDNA and hope that the values presented here will act as sound data for future research concerning the mutational-hazard hypothesis and plastid evolution in general.

Dataset Information

A cytochrome b5-containing plastid-located fatty acid desaturase from Chlamydomonas reinhardtii.

Publications

A cytochrome b5-containing plastid-located fatty acid desaturase from Chlamydomonas reinhardtii.

Similar Datasets

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