Eriksson Mats, Moseley Jeffrey L, Tottey Stephen, Del Campo Jose A, Quinn Jeanette, Kim Youngbae, Merchant Sabeeha
Department of Chemistry and Biochemistry, University of California, Los Angeles, California, 90095-1569, USA.
Genetics. 2004 Oct;168(2):795-807. doi: 10.1534/genetics.104.030460.
A genetic screen for Chlamydomonas reinhardtii mutants with copper-dependent growth or nonphotosynthetic phenotypes revealed three loci, COPPER RESPONSE REGULATOR 1 (CRR1), COPPER RESPONSE DEFECT 1 (CRD1), and COPPER RESPONSE DEFECT 2 (CRD2), distinguished as regulatory or target genes on the basis of phenotype. CRR1 was shown previously to be required for transcriptional activation of target genes like CYC6, CPX1, and CRD1, encoding, respectively, cytochrome c(6) (which is a heme-containing substitute for copper-containing plastocyanin), coproporphyrinogen III oxidase, and Mg-protoporphyrin IX monomethylester cyclase. We show here that CRR1 is required also for normal accumulation of copper proteins like plastocyanin and ferroxidase in copper-replete medium and for apoplastocyanin degradation in copper-deficient medium, indicating that a single pathway controls nutritional copper homeostasis at multiple levels. CRR1 is linked to the SUPPRESSOR OF PCY1-AC208 13 (SOP13) locus, which corresponds to a gain-of-function mutation resulting in copper-independent expression of CYC6. CRR1 is required also for hypoxic growth, pointing to a physiologically meaningful regulatory connection between copper deficiency and hypoxia. The growth phenotype of crr1 strains results primarily from secondary iron deficiency owing to reduced ferroxidase abundance, suggesting a role for CRR1 in copper distribution to a multicopper ferroxidase involved in iron assimilation. Mutations at the CRD2 locus also result in copper-conditional iron deficiency, which is consistent with a function for CRD2 in a pathway for copper delivery to the ferroxidase. Taken together, the observations argue for a specialized copper-deficiency adaptation for iron uptake in Chlamydomonas.
对莱茵衣藻具有铜依赖性生长或非光合表型的突变体进行的遗传筛选揭示了三个基因座，即铜反应调节因子1（CRR1）、铜反应缺陷1（CRD1）和铜反应缺陷2（CRD2），根据表型将它们区分为调节基因或靶基因。先前已证明CRR1是CYC6、CPX1和CRD1等靶基因转录激活所必需的，这些基因分别编码细胞色素c6（它是含血红素的铜蓝蛋白替代物）、粪卟啉原III氧化酶和镁原卟啉IX单甲酯环化酶。我们在此表明，CRR1对于铜充足培养基中铜蓝蛋白和铁氧化酶等铜蛋白的正常积累以及铜缺乏培养基中脱辅基铜蓝蛋白的降解也是必需的，这表明单一途径在多个水平上控制营养性铜稳态。CRR1与PCY1-AC208 13的抑制子（SOP13）基因座相关联，该基因座对应于一个功能获得性突变，导致CYC6的铜非依赖性表达。CRR1对于缺氧生长也是必需的，这表明铜缺乏与缺氧之间存在生理上有意义的调节联系。crr1菌株的生长表型主要是由于铁氧化酶丰度降低导致的继发性铁缺乏，这表明CRR1在将铜分配到参与铁同化的多铜铁氧化酶中发挥作用。CRD2基因座的突变也导致铜条件性铁缺乏，这与CRD2在铜传递到铁氧化酶的途径中的功能一致。综上所述，这些观察结果支持莱茵衣藻在铁吸收方面存在专门的铜缺乏适应性。
