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Published on February 7, 2008; 10.1104/pp.107.114868

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Received December 11, 2007
Accepted February 2, 2008

Identification of negative cis-acting elements in response to copper in the chloroplastic iron superoxide dismutase gene of the moss Barbula unguiculata

Miwa Nagae , Masaru Nakata , and Yohsuke Takahashi *

Department of Biological Science, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan

* Corresponding author; email: ytakahas{at}hiroshima-u.ac.jp.

Superoxide dismutases (SODs) are ubiquitous metalloenzymes that catalyze the dismutation of superoxide radicals. Chloroplasts have two isozymes, Cu/ZnSOD and FeSOD, encoded by nuclear genes. Since bryophytes are considered as the earliest land plants, they are one of the most interesting plant models for adaptation against oxidative stress. In a previous study, we found that the FeSOD gene was expressed under copper-deficient conditions and repressed under high-copper-supply conditions; on the other hand, the Cu/ZnSOD gene was induced by copper in a moss, Barbula unguiculata. The expression of Cu/ZnSOD and FeSOD is coordinately regulated at the transcriptional level depending on metal bioavailability. Here, using transgenic moss plants, we determined that the GTACT motif is a negative cis-acting element of the moss FeSOD gene in response to copper. Furthermore, we found that a plant-specific transcription factor, PpSBP2 (for SQUAMOSA promoter-binding protein), and its related proteins bound to the GTACT motif repressed the expression of the FeSOD gene. The moss FeSOD gene was negatively regulated by copper in transgenic tobacco plants, and the Arabidopsis (Arabidopsis thaliana) FeSOD gene promoter containing the GTACT motif was repressed by copper. Our results suggested that molecular mechanisms of GTACT motif-dependent transcriptional suppression by copper are conserved in land plants.






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