Chromera velia

Chromera veli
Scientific classification
Domain:	Eukaryota
Kingdom:	Chromalveolata
Superphylum:	Alveolata
Phylum:	Chromerida
Family:	Chromeraceae
Genus:	Chromera
Species:	Chromera velia

Chromera velia, also known as a "chromerid",^[1] is a photosynthetic alga^[2] in the superphylum Alveolata.

It has typical features of alveolates, being phylogenetically related to apicomplexa, and contains a photosynthetic plastid. C. velia uses this organelle as the primary energy source, thus being the closest known autotrophic organism to apicomplexans. It may retain a symbiotic relationship with the coral reef around it.^[3]

History

Chromera velia was first isolated by Dr Bob Moore (then at Carter Lab, University of Sydney) from the stony coral (Scleractinia, Cnidaria) Plesiastrea versipora (Faviidae) of Sydney Harbour, New South Wales, Australia (collectors Thomas Starke-Peterkovic and Les Edwards, December 2001).

It was also cultured by Dr Moore from the stony coral Leptastrea purpurea (Faviidae) of One Tree Island Great Barrier Reef, Queensland, Australia (collectors Karen Miller and Craig Mundy, November 2001).^[3]

Special features of C. velia plastid

The plastid of Chromera velia has 4 membranes and contains chlorophyll a, while chlorophyll c is missing. Unlike other eukaryotic algae which use UGG as codons for encoding tryptophan, the plastid of C. velia uses codon UGA to encode tryptophan at seven conserved position in the psbA gene. The UGA-Trp codon is characteristic of apicoplast plastids, and the mitochondria of various organisms, and until the discovery of C. velia, was unprecedented in any photosynthetic plastid. Discovery of this organism has provided a model to study the evolution of Apicomplexa.^[3]

Evolution

The discovery of Chromera velia and its unique plastid which is similar in origin to the apicoplasts, provides an important link in the evolutionary history of the apicomplexans. It is hypothesized that apicomplexans, with their unique relic chloroplast, the apicoplast, were once able to synthesize energy via photosynthesis by the apicoplast. However, this autotrophic mechanism was lost and apicomplexans have slowly evolved to become a parasitic species dependent on hosts for survival^[4].

Through a variety of phylogenetic tests on genes found in similar organisms, researchers were able to relate C. velia to dinoflagellates and apicomplexans. Subsequent research studies have also shown that the photosynthetic dinoflagellates, apicomplexans and C. velia share the same lineage, containing a red-algal-derived plastid.

With the use of additional DNA sequencing, the relationship between C. velia, dinoflagellates and apicoplexans was further confirmed. Genomic DNA of C. velia was extracted for PCR templates and sequences were compared with other species resulting in placement of C. velia on a phylogenetic branch close to the apicomplexans, with the help of biostatistical methods.^[3] Although researchers are still uncertain about why apicomplexans would sacrifice their photosynthetic ability and become parasitic, it is suggested that clues might be gathered by studying the evolution of the C. velia plastid relative to dinoflagellates.

Importance

One potentially important contribution that C. velia has to offer the community besides its role as a missing link between parasitic and algal species, is its use in studies aimed at finding a malaria vaccine. Parasites in the apicomplexan genus Plasmodium are the causative agents of malaria. Formerly scientists have targeted many drug treatments to the apicoplast in invading malarial cells, showing that the C. velia plastid could serve as a convenient model target for the development of antimalarial drugs. In the laboratory setting working with apicomplexan parasites can be difficult, because they must be plated on live host cells and do not always remain viable for long enough to run the necessary sequence of tests. Chromera velia, is more easily maintained alive, and is related to the parasites, so may potentially provide a laboratory model for work on developing antimalarial treatments. C. velia is able to live independently of its normal animal hosts and can be grown easily and cheaply in a laboratory setting. C. velia is available to purchase from the CCMP culture collection in Maine USA, and is backed up in other culture collections.

C. velia has helped put the spotlight back on the role of protist research, in various clinical and scientific applications regarding both algae and parasites. Strict separation of botanical protists (algae) and zoological protists (protozoa) has been conventional but C. velia may be regarded as a good example of a bridge.

References

1. ^ Takishita K, Yamaguchi H, Maruyama T, Inagaki Y (2009). Zhang, Baohong. ed. "A Hypothesis for the Evolution of Nuclear-Encoded, Plastid-Targeted Glyceraldehyde-3-Phosphate Dehydrogenase Genes in "Chromalveolate" Members". PLoS ONE 4 (3): e4737. doi:10.1371/journal.pone.0004737. PMC 2649427. PMID 19270733. http://dx.plos.org/10.1371/journal.pone.0004737. 
2. ^ k M, Janouskovec J, Oborní Chrudimský T, Lukes J, Lukeš, Julius (January 2009). "Evolution of the apicoplast and its hosts: from heterotrophy to autotrophy and back again". Int. J. Parasitol. 39 (1): 1–12. doi:10.1016/j.ijpara.2008.07.010. PMID 18822291. http://linkinghub.elsevier.com/retrieve/pii/S0020-7519(08)00361-5. 
3. ^ ^{a b c d} Moore RB; Oborník M; Janouskovec J; Chrudimský T; Vancová M; Green DH; Wright SW; Davies NW et al. (February 2008). "A photosynthetic alveolate closely related to apicomplexan parasites". Nature 451 (7181): 959–963. doi:10.1038/nature06635. PMID 18288187. http://www.nature.com/nature/journal/v451/n7181/full/nature06635.html. 
4. ^ http://www.abc.net.au/rn/scienceshow/stories/2008/2314746.htm