We investigated the gene structure and predicted amino acid sequence of the antioxidant enzyme 2-Cys peroxiredoxin (2-Cys Prx) in the raphidophyte Chattonella marina, which is a harmful algal bloom (HAB) species. The open reading frame of 2-Cys Prx was 585 bp long and encoded a protein consisting of 195 amino acids. The putative amino acid sequence contained two cysteine residues located at the 49th and 170th amino acid positions from the N-terminal methionine residue. The sequence also possessed 2-Cys Prx characteristic motifs, F (FFYPLDFTFVCPTEI) and EVCP. The position of the 2-Cys Prx gene relative to several others (ycf59–2-CysPrx–rpl35–rpl20) was the same as that found in the chloroplast genome in the raphidophyte Heterosigma akashiwo. Upstream of the 2-Cys Prx gene, possible TATA and GGA motifs recognized by nuclear-encoded plastid RNA polymerase (NEP), and a possible -10 box and -35 box recognized by plastid-encoded plastid RNA polymerase (PEP) were observed. We measured the transcript levels of 2-Cys Prx in C. marina cells grown under three different light intensities (0, 100, 1000 µmol photons m–2 s–1, 14-h light/8-h dark photoperiod) by quantitative PCR. The 2-Cys Prx transcript level in cells grown under the highest light intensity on day 3 was threefold that on day 0 but two lower light intensities resulted in relatively stable transcription levels. The 2-Cys Prx transcript level was significantly positively related to the H2O2 concentration per cell and the H2O2 scavenging activity per cell. These results suggest that C. marina 2-Cys Prx functions in the chloroplast and its transcription could be regulated by both NEP and PEP. Moreover, the 2-Cys Prx transcript level might increase to remove excessive H2O2 produced under strong light conditions in order to maintain cell proliferation activity.
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