Photosynthetic organisms often encounter oxidative stresses due to changes of environmental conditions. In this study, two glutathione peroxidase (GPX) homologous genes, namely NJ-18Gpx1 and NJ-18Gpx2, were identified in Chlorella sp. NJ-18, a single-celled green alga. The two NJ-18Gpx genes can produce 2 or 3 transcript variants by alternative splicing, predicted to encode 4 non-selenium GPX proteins (NS-GPX). Expression of the two genes was analyzed by quantitative RT-PCR in Chlorella sp. NJ-18 exposed to various treatments known to generate reactive oxygen species. Neutral red, a singlet oxygen-generating photosensitizer, significantly increased the expression of NJ-18Gpx1 within 5 h. Exposure of algal culture to UV-B for 3 h caused up-regulation of mRNA levels of NJ-18Gpx1 and NJ-18Gpx2 by 4- and 50-folds, respectively. Similar to CrGPX5 and CrGPX3 in Chlamydomonas reinhardtii, purified recombinant NJ-18GPXs showed activities of thioredoxin-dependent peroxidases that catalyze the reduction of hydrogen peroxide and organic hydroperoxides. The V-max values for NJ-18GPX1 toward different peroxides were approximately 10-fold higher than those for NJ-18GPX2. In addition, overexpression of NJ-18Gpx1 in Synechocystis sp. PCC 6803, a cyanobacterium, enhanced its tolerance to neutral red and H2O2. These results indicate that NJ-18GPXs can act as efficient peroxide scavengers protecting cells from oxidative damages in Chlorella. (C) 2012 Elsevier B.V. All rights reserved.
英文摘要:
Photosynthetic organisms often encounter oxidative stresses due to changes of environmental conditions. In this study, two glutathione peroxidase (GPX) homologous genes, namely NJ-18Gpx1 and NJ-18Gpx2, were identified in Chlorella sp. NJ-18, a single-celled green alga. The two NJ-18Gpx genes can produce 2 or 3 transcript variants by alternative splicing, predicted to encode 4 non-selenium GPX proteins (NS-GPX). Expression of the two genes was analyzed by quantitative RT-PCR in Chlorella sp. NJ-18 exposed to various treatments known to generate reactive oxygen species. Neutral red, a singlet oxygen-generating photosensitizer, significantly increased the expression of NJ-18Gpx1 within 5 h. Exposure of algal culture to UV-B for 3 h caused up-regulation of mRNA levels of NJ-18Gpx1 and NJ-18Gpx2 by 4- and 50-folds, respectively. Similar to CrGPX5 and CrGPX3 in Chlamydomonas reinhardtii, purified recombinant NJ-18GPXs showed activities of thioredoxin-dependent peroxidases that catalyze the reduction of hydrogen peroxide and organic hydroperoxides. The V-max values for NJ-18GPX1 toward different peroxides were approximately 10-fold higher than those for NJ-18GPX2. In addition, overexpression of NJ-18Gpx1 in Synechocystis sp. PCC 6803, a cyanobacterium, enhanced its tolerance to neutral red and H2O2. These results indicate that NJ-18GPXs can act as efficient peroxide scavengers protecting cells from oxidative damages in Chlorella. (C) 2012 Elsevier B.V. All rights reserved.
