Plant Molecular Biology 46: 395–408, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
The glutathione peroxidase homologous gene from Chlamydomonas
reinhardtii is transcriptionally up-regulated by singlet oxygen
Urs Leisinger, Karin Rüfenacht, Beat Fischer, Manuel Pesaro, Arik Spengler, Alexander J. B.
Zehnder and Rik I. L. Eggen
Department of Environmental Microbiology and Molecular Ecotoxicology, Swiss Federal Institute for Environ-
mental Science and Technology (EAWAG), Ueberlandstrasse 133, P.O. Box 611, 8600 Duebendorf, Switzerland
author for correspondence; e-mail email@example.com)
Received 17 March 2000; accepted in revised form 11 January 2001
Key words: glutathione peroxidase, organic hydroperoxide, photosensitizer, singlet oxygen, transcriptional
The glutathione peroxidase homologous gene (Gpxh gene) in Chlamydomonas reinhardtii is up-regulated un-
der oxidative stress conditions. The Gpxh gene showed a remarkably strong and fast induction by the singlet
oxygen-generating photosensitizers neutral red, methylene blue and rose Bengal. The Gpxh mRNA levels strongly
increased, albeit much more slowly, upon exposure to the organic hydroperoxides tert-butyl hydroperoxide (t-
BOOH) and cumene hydroperoxide. In contrast, the Gpxh mRNA levels were only weakly induced by exposure
to the superoxide-generating compound paraquat and by hydrogen peroxide. A comparison of the Gpxh mRNA
levels with those of the heat shock protein HSP70A and the iron superoxide dismutase gene showed qualitative and
quantitative differences for the three genes under oxidative stress conditions tested. The Gpxh gene is speciﬁcally
induced by singlet-oxygen photosensitizers and the relative induction by other compounds is much weaker for
Gpxh than for the other genes investigated. Using Gpxh promoter fusions with the arylsulfatase reporter gene,
we have shown that the Gpxh was transcriptionally up-regulated by singlet-oxygen photosensitizers. It is also
shown that the Gpxh promoter contains a region between 104 and 179 bp upstream of the transcription start that
is responsible for the mRNA up-regulation upon exposure to
but not t-BOOH. Within this region a regulatory
sequence homologous to the mammalian cAMP response element (CRE) and activator protein 1 (AP-1) binding
site was identiﬁed within a 16 bp palindrome.
, singlet oxygen; CU-OOH, cumene hydroperoxide; Fesod, iron-dependent superoxide dis-
mutase gene; Gpxh, glutathione peroxidase homologous; Hsp70a, heat shock protein 70A; MB, methylene blue;
NR, neutral red; RB, rose Bengal; TAP, Tris-acetate-phosphate; t-BOOH, tert-butyl hydroperoxide.
Molecular oxygen is essential for many organisms,
and at the same time causes damage to cells. Although
molecular oxygen is not very reactive, it can be acti-
vated to the reactive oxygen species (ROS) superoxide
The nucleotide sequence data reported will appear in the EMBL,
GenBank and DDBJ Nucleotide Sequence Databases under the
accession number AF014927.
radical anion (O
), hydrogen peroxide (H
hydroxyl radical (OH
) by partial reduction. In addi-
tion, molecular oxygen can be activated to the ROS
singlet oxygen (
) either by transfer of excitation
energy or in redox reactions (Halliwell and Gutteridge,
1989; Elstner, 1991; Bensasson et al., 1993). ROS
are produced during normal metabolic activities and
their generation augments upon exposure to strong il-
lumination, UV irradiation, pollutants or pathogens.