Regulation by copper of the expression of plastocyanin and cytochrome c552 in Chlamydomonas reinhardi.

Abstract

Plastocyanin and cytochrome c552 are interchangeable electron carriers in the photosynthetic electron transfer chains of some cyanobacteria and green algae (P. M. Wood, Eur. J. Biochem. 87:9-19, 1978; G. Sandmann et al., Arch. Microbiol. 134:23-27, 1983). Chlamydomonas reinhardi cells respond to the availability of copper in the medium and accordingly accumulate either plastocyanin (if copper is available) or cytochrome c552 (if copper is not available). The response occurs in both heterotrophically and phototrophically grown cells. We have studied the molecular level at which this response occurs. No immunoreactive polypeptide is detectable under conditions where the mature protein is not spectroscopically detectable. Both plastocyanin and cytochrome c552 appear to be translated (in vitro) from polyadenylated mRNA as precursors of higher molecular weight. RNA was isolated from cells grown either under conditions favorable for the accumulation of plastocyanin (medium with Cu2+) or for the accumulation of cytochrome c552 (without Cu2+ added to the medium). Translatable mRNA for preapoplastocyanin was detected in both RNA preparations, although mature plastocyanin was detected in C. reinhardi cells only when copper was added to the culture. Translatable mRNA for preapocytochrome, on the other hand, was detected only in cells grown under conditions where cytochrome c552 accumulates (i.e., in the absence of copper). We conclude that copper-mediated regulation of plastocyanin and cytochrome c552 accumulation is effected at different levels, the former at the level of stable protein and the latter at the level of stable mRNA.

Specific sequence elements in the 5′ untranslated regions of rbcL and atpB gene mRNAs stabilize transcripts in the chloroplast of Chlamydomonas reinhardtii

“…Genomic DNA and total RNA were isolated from C. reinhardtii as described (Dellaporta et al+, 1983;Merchant & Bogorad, 1986;Salvador et al+, 1993a)+ DNA was isolated from cultures growing under continuous illumination+ RNA was isolated from cultures growing in a 12-h light/12-h dark regime+ When not specified differently, time points for isolation of total RNA were 11 h in the dark or 1 h in the light for transformants carrying rbc L:GUS genes and atpB:GUS genes, respectively+ The presence of the chimeric GUS gene constructs in Chlamydomonas chloroplast transformants was analyzed by DNA slot-blot hybridizations using the random primer-labeled (Feinberg & Vogelstein, 1983) GUS sequence as probe+ The relative abundance of GUS transcripts in Chlamydomonas chloroplast transformants was determined by RNA gel (northern) blots+ DNA and RNA blots were hybridized to radiolabeled probes and processed for autoradiography as described (Church & Gilbert, 1984;Blowers et al+, 1990)+…”

Import, Targeting, and Processing of a Plant Polyphenol Oxidase

“…In Cudeficient Chlamydomonas, Cyt c552 replaced PC in the photosynthetic electron transport chain. It was suggested that Cu2+ hals a regulatory role in the import and processing of pPC by plastids (Merchant and Bogorad, 1986).…”

Regulation of Copper Homeostasis by Micro-RNA in Arabidopsis

“…Whereas CSD1 and CSD2 expression was shut off when copper is limiting, the iron-requiring FSD1 was up-regulated. In contrast, the PC level is likely to be a consequence of copper delivery to the thylakoid lumen because apo-PC without copper is unstable (17,18). The regulation of SOD expression would allow efficient delivery of limited copper to PC, which is essential, yet also maintain plastid SOD activity.…”