Altered Cu metabolism and differential transcription of Cu/ZnSod genes in a Cu/ZnSOD-deficient mutant of maize: evidence for a Cu-responsive transcription factor.
Maize inbred line A351 exhibits extremely low levels of Cu/Zn superoxide dismutase (SOD) isozymes, three cytosolic and one chloroplastic, which are increased by supplying copper to near-toxic concentrations. Activities of the copper enzymes cytochrome c oxidase and ascorbate oxidase are also reduced. The level of expression of the maize copper chaperone for SOD is normal to elevated. The gene transcript encoding chloroplastic SOD-1 is present at normal levels, whereas RNA levels of the cytosolic SODs are low and increase with added copper, suggesting a promoter element and copper-dependent transcription factor common to the three genes. Although a reduced level of high-affinity copper transport in A351 cannot be ruled out, high transcript levels of a constitutively expressed metallothionein, suggesting increased copper chelation capacity and creating a general copper-deprivation effect, seem to be a likely cause of the reduced levels of copper enzyme activity and Cu/ZnSod gene transcripts. While exogenous copper does not affect the wild-type SOD activity or protein, it increases wild-type Cu/ZnSod transcript levels in a response similar to that of several yeast genes involved in copper sequestration and antioxidant defense. A sequence that is highly homologous to those of the copper-responsive transcription factors ACE1 (Saccharomyces cerevisiae) and AMT1 (Candida glabrata) is present in the promoters of three maize Cu/ZnSod genes.
Ruzsa
Stephanie M
SM
Department of Genetics, North Carolina State University, Raleigh, North Carolina 27695-7614, USA.
Scandalios
John G
JG
D003300:Copper / Q000378:metabolism* / Q000633:toxicity*; D003576:Electron Transport Complex IV / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D017343:Genes, Plant; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008668:Metallothionein / Q000096:biosynthesis; D008954:Models, Biological; D010269:Paraquat / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D013482:Superoxide Dismutase / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects*; D003313:Zea mays / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology
D007527:Isoenzymes; D010940:Plant Proteins; D014157:Transcription Factors; D003300:Copper; D008668:Metallothionein; D013482:Superoxide Dismutase; D003576:Electron Transport Complex IV; D015032:Zinc; D010269:Paraquat