This Article Full Text Full Text (PDF) Supplemental material Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by de Koning, A. P. Articles by Keeling, P. J. Search for Related Content PubMed PubMed Citation Articles by de Koning, A. P. Articles by Keeling, P. J.

 Previous Article  |  Next Article 

Eukaryotic Cell, October 2004, p. 1198-1205, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1198-1205.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Nucleus-Encoded Genes for Plastid-Targeted Proteins in Helicosporidium: Functional Diversity of a Cryptic Plastid in a Parasitic Alga

Audrey P. de Koning^* and Patrick J. Keeling

Program in Evolutionary Biology, Canadian Institute for Advanced Research, and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada

Received 15 April 2004/ Accepted 12 July 2004

Plastids are the organelles of plants and algae that house photosynthesis and many other biochemical pathways. Plastids contain a small genome, but most of their proteins are encoded in the nucleus and posttranslationally targeted to the organelle. When plants and algae lose photosynthesis, they virtually always retain a highly reduced "cryptic" plastid. Cryptic plastids are known to exist in many organisms, although their metabolic functions are seldom understood. The best-studied example of a cryptic plastid is from the intracellular malaria parasite, Plasmodium, which has retained a plastid for the biosynthesis of fatty acids, isoprenoids, and heme by the use of plastid-targeted enzymes. To study a completely independent transformation of a photosynthetic plastid to a cryptic plastid in another alga-turned-parasite, we conducted an expressed sequence tag (EST) survey of Helicosporidium. This parasite has recently been recognized as a highly derived green alga. Based on phylogenetic relationships to other plastid homologues and the presence of N-terminal transit peptides, we have identified 20 putatively plastid-targeted enzymes that are involved in a wide variety of metabolic pathways. Overall, the metabolic diversity of the Helicosporidium cryptic plastid exceeds that of the Plasmodium plastid, as it includes representatives of most of the pathways known to operate in the Plasmodium plastid as well as many others. In particular, several amino acid biosynthetic pathways have been retained, including the leucine biosynthesis pathway, which was only recently recognized in plant plastids. These two parasites represent different evolutionary trajectories in plastid metabolic adaptation.

---

* Corresponding author. Mailing address: 3529-6270 University Blvd., Vancouver, BC V6T 1Z4, Canada. Phone: (604) 822-2845. Fax: (604) 822-6089. E-mail: apdk{at}interchange.ubc.ca.

Supplemental material for this article may be found at http://ec.asm.org/.

---

Eukaryotic Cell, October 2004, p. 1198-1205, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1198-1205.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• O'Brien, E. A., Koski, L. B., Zhang, Y., Yang, L., Wang, E., Gray, M. W., Burger, G., Lang, B. F. (2007). TBestDB: a taxonomically broad database of expressed sequence tags (ESTs). Nucleic Acids Res 35: D445-D451 [Abstract] [Full Text]  
• Atteia, A., van Lis, R., Beale, S. I. (2005). Enzymes of the Heme Biosynthetic Pathway in the Nonphotosynthetic Alga Polytomella sp.. Eukaryot Cell 4: 2087-2097 [Abstract] [Full Text]  
• Borza, T., Popescu, C. E., Lee, R. W. (2005). Multiple Metabolic Roles for the Nonphotosynthetic Plastid of the Green Alga Prototheca wickerhamii. Eukaryot Cell 4: 253-261 [Abstract] [Full Text]