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Eukaryotic Cell, October 2002, p. 736-757, Vol. 1, No. 5
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.5.736-757.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Copper-Dependent Iron Assimilation Pathway in the Model Photosynthetic Eukaryote Chlamydomonas reinhardtii

Sharon La Fontaine,1,2 Jeanette M. Quinn,1,{dagger} Stacie S. Nakamoto,1 M. Dudley Page,1 Vera Göhre,1,{ddagger} Jeffrey L. Moseley,1 Janette Kropat,1 and Sabeeha Merchant1,3*

Department of Chemistry and Biochemistry,1 Molecular Biology Institute, University of California, Los Angeles, Los Angeles, California 90095-1569,3 The Centre for Cellular and Molecular Biology, School of Biological and Chemical Sciences, Deakin University, Melbourne, Victoria, Australia2

Received 11 April 2002/ Accepted 24 July 2002

The unicellular green alga Chlamydomonas reinhardtii is a valuable model for studying metal metabolism in a photosynthetic background. A search of the Chlamydomonas expressed sequence tag database led to the identification of several components that form a copper-dependent iron assimilation pathway related to the high-affinity iron uptake pathway defined originally for Saccharomyces cerevisiae. They include a multicopper ferroxidase (encoded by Fox1), an iron permease (encoded by Ftr1), a copper chaperone (encoded by Atx1), and a copper-transporting ATPase. A cDNA, Fer1, encoding ferritin for iron storage also was identified. Expression analysis demonstrated that Fox1 and Ftr1 were coordinately induced by iron deficiency, as were Atx1 and Fer1, although to lesser extents. In addition, Fox1 abundance was regulated at the posttranscriptional level by copper availability. Each component exhibited sequence relationship with its yeast, mammalian, or plant counterparts to various degrees; Atx1 of C. reinhardtii is also functionally related with respect to copper chaperone and antioxidant activities. Fox1 is most highly related to the mammalian homologues hephaestin and ceruloplasmin; its occurrence and pattern of expression in Chlamydomonas indicate, for the first time, a role for copper in iron assimilation in a photosynthetic species. Nevertheless, growth of C. reinhardtii under copper- and iron-limiting conditions showed that, unlike the situation in yeast and mammals, where copper deficiency results in a secondary iron deficiency, copper-deficient Chlamydomonas cells do not exhibit symptoms of iron deficiency. We propose the existence of a copper-independent iron assimilation pathway in this organism.

* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of California, Los Angeles, P.O. Box 951569, 607 Charles E. Young Dr. East, Los Angeles, CA 90095-1569. Phone: (310) 825-8300. Fax: (310) 206-1035. E-mail: merchant{at}chem.ucla.edu.

{dagger} Present address: Stratagene, La Jolla, Calif.

{ddagger} Present address: Département de Biologie Moléculaire, Université de Genève, Geneva, Switzerland.

Eukaryotic Cell, October 2002, p. 736-757, Vol. 1, No. 5
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.5.736-757.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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