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Adaptation of scenedesmus obliquus (chlorophyceae) to copper-deficiency: transcriptional regulation of pcy1 but not cpx1

Quinn, Jeanette M., Merchant, Sabeeha
Journal of phycology 1999 v.35 no.6 pp. 1253-1263
Chlamydomonas reinhardtii, Scenedesmus obliquus, clones, complementary DNA, copper, genes, messenger RNA, proteins, transcription (genetics)
In contrast to the situation in Chlamydomonas reinhardtii, plastocyanin expression in the green alga Scenedesmus obliquus (Turp.) Kütz. (Chlorophyceae) is regulated by copper ion availability at the level of both protein and mRNA accumulation. To study the mechanism of copper-dependent mRNA accumulation, plastocyanin-encoding genomic and cDNA clones have been isolated and sequenced. The single nuclear S. obliquus Pcy1 gene contains two introns and a bipartite transit peptide sequence typical of plastid lumen-localized proteins. Despite the similarity of the S. obliquus and Chlamydomonas reinhardtii Pcy1 genes, the S. obliquus Pcy1 gene was not expressed from its own promoter, nor could the S. obliquus Pcy1 promoter drive expression of a C. reinhardtii gene when it was introduced into the genome of C. reinhardtii cells. Using the cDNA clone as a probe, copper-responsive regulation of Pcy1 expression was further characterized in S. obliquus. Experiments examining the time course of Pcy1 degradation on depletion of copper argue against a specific mechanism for Pcy1 mRNA decay in S. obliquus, suggesting that the copper-responsive change in abundance occurs through transcriptional regulation. The Cpx1 gene (encoding coproporphyrinogen III oxidase) also responds differently to changes in cellular copper status in S. obliquus compared to C. reinhardtii. Whereas Cpx1 is highly induced in copper-deficient cultures of C. reinhardtii, in S. obliquus the Cpx1 gene is not copper responsive.