AtCCS is a functional homolog of the yeast copper chaperone Ccs1/Lys7

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517

479

In plants, copper is an essential micronutrient required for photosynthesis. Two of the most abundant copper proteins, plastocyanin and copper/zinc superoxide dismutase, are found in chloroplasts. Whereas plastocyanin is essential for photo-autotrophic growth, copper/zinc superoxide dismutase is dispensable and in plastids can be replaced by an iron superoxide dismutase when copper is limiting. The down-regulation of copper/zinc superoxide dismutase expression in response to low copper involves a microRNA, miR398. Interestingly, in Arabidopsis and other plants, three additional microRNA families, miR397, miR408, and miR857, are predicted to target the transcripts for the copper protein plantacyanin and members of the laccase copper protein family. We confirmed the predicted targets of miR397, miR408, and miR857 experimentally by cleavage site analysis. To study the spatial expression pattern of these microRNAs and the effect of copper on their expression, we analyzed Arabidopsis grown hydroponically on different copper regimes. On low amounts of copper the plants accumulated miR397, miR408, and miR857. The microRNA expression pattern was negatively correlated with the accumulation of transcripts for plantacyanin and laccases. Furthermore, the expression of other laccases that are not predicted targets for known microRNAs was similarly regulated in response to copper. For some of these laccases, the regulation was disrupted in a microRNA maturation mutant (hen1-1), suggesting the presence of other copper-regulated microRNAs. Thus, in Arabidopsis, microRNA-mediated down-regulation is a general mechanism to regulate nonessential copper proteins. We propose that this mechanism allows plants to save copper for the most essential functions during limited copper supply.

Section: Discussionmentioning

confidence: 99%

“…In chloroplasts, another SOD called FSD1 utilizes iron as the cofactor. copper availability was found to regulate the expression of CCS, CSD1, CSD2, and FSD1 in Arabidopsis and other dicot plant species (15)(16)(17). When copper levels are sufficient, the Cu,Zn-SOD proteins are expressed, and FSD1 expression is shut-off.…”

mentioning

confidence: 99%

MicroRNA-mediated Systemic Down-regulation of Copper Protein Expression in Response to Low Copper Availability in Arabidopsis

Abdel‐Ghany

Pilon

2008

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517

479

“…CCS has been characterized in fungi, animals, and plants (14,16,24,(53)(54)(55) indicating that this gene was present prior to the evolutionary divergence of eukaryotes and was subsequently lost in C. elegans. However, copper metabolism in C. elegans appears quite similar to other eukaryotes in many respects, and of the three known soluble copper carriers identified, C. elegans is missing only CCS.…”

Section: Discussionmentioning

confidence: 99%

Activation of CuZn Superoxide Dismutases from Caenorhabditis elegans Does Not Require the Copper Chaperone CCS

Jensen

Culotta

2005

104

Reactive oxygen species are produced as the direct result of aerobic metabolism and can cause damage to DNA, proteins, and lipids. A principal defense against reactive oxygen species involves the superoxide dismutases (SOD) that act to detoxify superoxide anions. Activation of CuZn-SODs in eukaryotic cells occurs posttranslationally and is generally dependent on the copper chaperone for SOD1 (CCS), which inserts the catalytic copper cofactor and catalyzes the oxidation of a conserved disulfide bond that is essential for activity. In contrast to other eukaryotes, the nematode Caenorhabditis elegans does not contain an obvious CCS homologue, and we have found that the C. elegans intracellular CuZn-SODs (wSOD-1 and wSOD-5) are not dependent on CCS for activation when expressed in Saccharomyces cerevisiae. CCS-independent activation of CuZn-SODs is not unique to C. elegans; however, this is the first organism identified that appears to exclusively use this alternative pathway. As was found for mammalian SOD1, wSOD-1 exhibits a requirement for reduced glutathione in CCS-independent activation. Unexpectedly, wSOD-1 was inactive even in the presence of CCS when glutathione was depleted. Our investigation of the cysteine residues that form the disulfide bond in wSOD-1 suggests that the ability of wSODs to readily form this disulfide bond may be the key to obtaining high levels of activation through the CCS-independent pathway. Overall, these studies demonstrate that the CuZn-SODs of C. elegans have uniquely evolved to acquire copper without the copper chaperone and this may reflect the lifestyle of this organism.

“…Two P-type ATPases, PAA1 and PAA2, are required for efficient copper delivery across the plastid envelope and the thylakoid membrane, respectively, in Arabidopsis (11,12). Once copper is transported into the stroma by PAA1, it can be transferred to the stromal form of CCS, which can target it to stromal CSD2 (10,13). On the other hand, stromal copper can also be transferred to PC via PAA2.…”

mentioning

confidence: 99%

Regulation of Copper Homeostasis by Micro-RNA in Arabidopsis

Yamasaki

Abdel‐Ghany

Cohu

et al. 2007

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387

383

Major copper proteins in the cytoplasm of plant cells are plastocyanin, copper/zinc superoxide dismutase, and cytochrome c oxidase. Under copper limited conditions, expression of copper/ zinc superoxide dismutase is down-regulated and the protein is replaced by iron superoxide dismutase in chloroplasts. We present evidence that a micro-RNA, miR398, mediates this regulation in Arabidopsis thaliana, by directing the degradation of copper/zinc superoxide dismutase mRNA when copper is limited. Sequence analysis indicated that the transcripts encoding cytosolic copper/zinc superoxide dismutase and COX5b-1, a subunit of the mitochondrial cytochrome c oxidase, are also targeted by miR398. This regulation via miR398 takes place in response to changes in a low range of copper levels (0.2-0.5 M), indicating that miR398 is involved in a response to copper limitation. On the other hand, another major copper protein, plastocyanin, which is involved in photosynthetic electron flow and is essential in higher plants, was not regulated via miR398. We propose that miR398 is a key factor in copper homeostasis in plants and regulates the stability of mRNAs of major copper proteins under copper-limited conditions.