Regulated Copper Uptake in Chlamydomonas reinhardtii in Response to Copper Availability

Hill, Kent L.; Hassett, Richard; Kosman, Daniel J.; Merchant, Sabeeha

doi:10.1104/pp.112.2.697

Cited by 80 publications

(100 citation statements)

References 41 publications

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“…4). This is within the same magnitude of the reported K m for Cu 21 uptake in Chlamydomonas reinhardtii (Hill et al, 1996). The reported ratio of PGSK to Fe 21 interaction is 3:1 (Petrat et al, 1999).…”

Section: Discussionsupporting

confidence: 73%

Copper Transport Across Pea Thylakoid Membranes

2004

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The initial rate of Cu2+ movement across the thylakoid membrane of pea (Pisum sativum) chloroplasts was directly measured by stopped-flow spectrofluorometry using membranes loaded with the Cu2+-sensitive fluorophore Phen Green SK. Cu2+ transport was rapid, reaching completion within 0.5 s. The initial rate of uptake was dependent upon Cu2+ concentration and saturated at about 0.6 μm total Cu2+. Cu2+ uptake was maximal at a thylakoid lumen pH of 7.0. Cu2+ transport was inhibited by Zn2+ but was largely unaffected by Mn2+ and Cu+. Zn2+ inhibited Cu2+ transport to a maximum of 60%, indicating that there may be more than one transporter for copper in pea thylakoid membranes

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Section: Discussionsupporting

confidence: 73%

Copper Transport Across Pea Thylakoid Membranes

2004

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“…EUKARYOT. CELL on May 11, 2018 by guest http://ec.asm.org/ ciencies versus those to iron deficiencies (42). In this work, we provide substantial evidence for the involvement of an MCO in iron metabolism ( Fig.…”

supporting

confidence: 55%

“…With its simple growth requirements C. reinhardtii is a valuable experimental model for the study of metalloprotein biosynthesis (72,75) and metal-responsive gene regulation in photosynthetic organisms (71). As in other organisms, iron uptake by Chlamydomonas involves reductases (22,42,67,114) that are induced in iron deficiency and may be the same enzyme as that induced in copper-deficient (ϪCu) cells (42). Iron uptake is also induced, although to a lesser extent than Fe 3ϩ reduction (22).…”

mentioning

confidence: 99%

Copper-Dependent Iron Assimilation Pathway in the Model Photosynthetic EukaryoteChlamydomonas reinhardtii

Fontaine

Quinn²,

Nakamoto³

et al. 2002

Eukaryot Cell

185

209

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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.While iron is abundant in the environment, it is present in the insoluble ferric [Fe(III)] state, so that its bioavailability is low (16). Yet iron is an essential micronutrient for all organisms because it functions as a cofactor in enzymes that catalyze redox reactions in fundamental metabolic processes. Iron exhibits stable, redox-interchangeable ionic states with the potential to generate less stable electron-deficient intermediates during multielectron redox reactions involving oxygen chemistry (16). Therefore, organisms are challenged with the acquisition of sufficient iron to meet cellular metabolic requirements while avoiding uncontrolled intracellular chemistry. This is accomplished via the operation of iron homeostatic mechanisms. The essential features of iron metabolism include assimilation and distribution, storage and sequestration, and utilization and allocation. The assimilatory pathway can be further subdivided into reduction of insoluble ferric species to more soluble ferrous species and uptake into the cell, followed by intracellular transport and intraorganellar distribution. The storage and sequestration of iron involve loading of cellular proteins as well as compartmentalization into organelles like vacuoles and plastids, which in turn requires proteins for transport into and out of these compartm...

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“…Such a Cu uptake system has been established in other eukaryotes. For example, in the freshwater green alga Chlamydomonas reinhardtii, Cu uptake is associated with a cupric reductase (Hill et al 1996). In yeast, Cu uptake is well characterized and is facilitated by both low-and highaffinity transporters.…”

Section: Discussionmentioning

confidence: 99%

The effects of Cu and Fe availability on the growth and Cu:C ratios of marine diatoms

Annett

Lapi

Ruth

et al. 2008

Limnology & Oceanography

112

107

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We investigated the effects of copper (Cu) and iron (Fe) availability on the growth rates, cellular Cu content, and steady-state Cu uptake rates of eight species of centric diatoms (coastal and oceanic strains). Whereas Fe and Cu availability had a significant effect on the growth rates of both costal and oceanic diatoms, an interaction between Fe and Cu availability and growth rates was only observed for the oceanic diatoms. Determination of cellular Cu : carbon (C) quotas using the radiotracers 67 Cu and 14 C revealed that under Cu-sufficient conditions oceanic diatoms had elevated Cu : C ratios relative to coastal strains, regardless of Fe availability. Two species (one oceanic and one coastal) significantly increased their Cu demands in response to Fe limitation, indicating upregulation of the Cu-dependent high-affinity Fe uptake system in these organisms. The changes in cellular Cu : C ratios were accompanied by variations in steady-state Cu uptake rates. Thus, in some cases Cu uptake rates appear to be regulated by the cell in response to Fe availability. Rates of Cu acquisition also responded significantly to Cu variability. The variation in Cu uptake was more closely correlated with changes in total Cu concentration in the medium than in inorganic, free Cu concentrations, implying that organic Cu complexes may be bioavailable to diatoms. These findings indicate a greater biological role for Cu than was previously thought in open ocean regions.

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Regulated Copper Uptake in Chlamydomonas reinhardtii in Response to Copper Availability

Cited by 80 publications

References 41 publications

Copper Transport Across Pea Thylakoid Membranes

Copper Transport Across Pea Thylakoid Membranes

Copper-Dependent Iron Assimilation Pathway in the Model Photosynthetic EukaryoteChlamydomonas reinhardtii

The effects of Cu and Fe availability on the growth and Cu:C ratios of marine diatoms

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