Functional Study Of Caspase3 And Glutamine Synthetase In The Environmental Stress Of Pocillopora Damicornis

Coral reef ecosystem is one of the most important marine ecosystems,which has high primary productivity and biodiversity.However,due to the impact of global climate change,the coral reef ecosystem is facing a serious environmental crisis,and large areas of coral have died.Apoptosis and nitrogen metabolism are important physiological activities of coral reef.which involved in the process of adapting to the environment.In this study,we studied the functional of Caspase3 and glutamine synthetase in the environmental stress of P.damicornis.The whole cDNA sequence of PdCaspase3 and PdGS was obtained through RACE PCR method.The whole length of PdCaspase3 was of 1504bp.The ORF encoded a polypeptide containing 344 amino acids with a molecular weight of 39.19 kDa.A CASc domain was predicted in the peptide,and it displayed caspase3-like activity which catalyzed the reaction of DEVD-p-nitroanilide cleavage.The whole length of PdGS was of 1958bp.The ORF encoded a polypeptide containing 362 amino acids with a molecular weight of 40.68 kDa.A glutamine binding domain(Gln-synt_C)was predicted in the peptide.After 24h high temperature stress,the expression of PdCaspase3 mRNA and Caspase3 activity increased obviously(p<0.05),and reached the highest expression level.After 12 h ammonium enrichment stress,the expression of PdCaspase3 mRNA and Caspase3 activity was significantly higher than that in the blank group and the control group(P<0.05).The expression of PdGS mRNA and GS activity was significantly higher than that in the blank group and the control group(P<0.05),reached the highest level of expression.Furthermore,there was not significant change in the expression level of PdCaspase3 and PdGS in the control group during whole experiment process.The research shows that PdCaspase3 and PdGS involved in the stress response to high temperature and elevated ammonium in stony coral P.damicornisthe.When the coral is subjected to environmental stress,a large number of oxygen free radicals are produced by the symbiotic algae,and the resulting excess oxidation pressure further activates the apoptosis mediated by coral Caspase3,which will lead to the excretion of the symbiotic zooxanthellae alga in vitro and thus cause bleaching and death of the coral.Under ammonium enrichment,nitrogen assimilation mediated by GS is significantly enhanced,which can not only reduce the toxicity of ammonia to coral,but also maintain the nitrogen limitation of symbiotic zooxanthellae algae.On the other hand,under the stress of ammonium enrichment,coral can induce glutathione to reduce ROS damage through glutamine.,It also regulates the interaction between glutamine tRNA synthetase(QRS)and ASK-1,thereby inhibiting the activity of ASK-1 and indirectly regulating the process of Caspase3 mediated apoptosis.This study identified the molecular mechanism of coral blanching induced by environmental stress through Caspase3 mediated apoptosis.It also reveals that environmental stress activated the regulation of GS on the metabolism of coral symbionts and the mechanism of coral induced bleaching induced by Caspase3 mediated apoptosis,which provides theoretical support for the protection and rational development of coral reef ecosystem resources.