Possible roles of glutamine synthetase in responding to environmental changes in a scleractinian coral
Glutamine synthetase is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine. In this study, the activity and responses of glutamine synthetase towards environmental changes were investigated in the scleractinian coral Pocillopora damicornis. The identified glutamine synthetase (PdGS) was comprised of 362 amino acids and predicted to contain one Gln-synt_N and one Gln-synt_C domain. Expression of PdGS mRNA increased significantly after 12 h (1.28-fold, p < 0.05) of exposure to elevated ammonium, while glutamine synthetase activity increased significantly from 12 to 24 h, peaking at 12 h (54.80 U mg−1, p < 0.05). The recombinant protein of the mature PdGS (rPdGS) was expressed in E. coli BL21, and its activities were detected under different temperature, pH and glufosinate levels. The highest levels of rPdGS activity were observed at 25 °C and pH 8 respectively, but decreased significantly at lower temperature, and higher or lower pH. Furthermore, the level of rPdGS activities was negatively correlated with the concentration of glufosinate, specifically decreasing at 10−5 mol L−1 glufosinate to be less than 50% (p < 0.05) of that in the blank. These results collectively suggest that PdGS, as a homologue of glutamine synthetase, was involved in the nitrogen assimilation in the scleractinian coral. Further, its physiological functions could be suppressed by high temperature, ocean acidification and residual glufosinate, which might further regulate the coral-zooxanthella symbiosis via the nitrogen metabolism in the scleractinian coral P. damicornis.
KeywordsGlutamine synthetase Scleractinian coral Nitrogen assimilation Environmental factor Glufosinate
The authors were grateful to all the laboratory members for continuous technical advice and helpful discussion. We thanked Zongxiu Wu for his kind helps with the collection and culturing of the coral samples. This research was supported by a Grant (No. 31772460) from National Science Foundation of China, Natural Science Foundation (No. 20164158) of Hainan Province, and the scientific research foundation (kyqd1554) of Hainan University.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All the experiments were conducted according to the regulations of local and central government, and the study protocol was approved by Hainan University.
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