The Recognition Activities Of A Galectin To Pathogen And Symbiont In The Scleractinian Coral Pocillopora Damicornis

As one of the three typical marine ecosystems,the importance of coral reef ecosystem is self-evident.However,coral reef ecosystem is now facing an unprecedented test.The rise of the sea surface temperature has been destroying the symbiosis between coral and Symbiodinium,which leads to the effluxion or death of Symbiodinium and the bleaching of scleractinian corals.With the frequent occurrence of abnormal climate,the symbiosis on which corals live has been destroying,and numerous corals have been bleaching.Lectins play very important roles in the symbiosis between coral and Symbiodinium,In order to reveal the mechanism of symbiosis between scleractinian coral and Symbiodinium,Pocillopora damicornis was chosen as study subject and studied the recognition activity of lectin to Symbiodinium and pathogens under high temperature.In this study,a cDNA sequence encoding one galectin was cloned in P.damicornis?PdGLT-1?.PdGLT-1 cDNA comprised of 115 bp 5'-untranslated region?UTR?,689 bp 3'-UTR and 882 bp Open Reading Frame?ORF?encoding a polypeptide of 293 amino acid residues.Molecular weight of the PdGLT-1 mature peptide?without signal peptide?was calculated to be 28.21kDa.The deducted PdGLT-1 protein was found to share highest amino acid sequence similarity?99%?with galectin from Stylophora pistillata?XP₀22806650.1?and was composed of one signal peptide,one Collagen domain and one Gal-Lectin domain.After PdGLT-1 recombinant protein?rPdGLT-1?was expressed and purified in vitro,its binding activities to bacteria and symbiont were determined using western blotting method.Results showed that rPdGLT-1 was able to bind to and agglutinate gram-positive bacterium Streptococcus mutans.gram-negative bacteria Vibrio ·oralliilyticus and Escherichia coli,with the highest activity for V.coralliilyticus.The bound rPdGLT-1 to Symbiodinium?10-104 cells mL-1?was detectable,and its binding ability was concentration-dependent.Furthermore,dual binding activities were determined under different temperatures?20?25,30 and 35“C?,and the optimal temperatures were found to be 25 and 30? for V.coralliilyticus and Symbiodinium,respectively.However,their recognition activities were repressed under high temperature?>30oC?.These results indicate that PdGLT-1 has recognition ability to pathogenic bacteria and Syobiodinium.For the Symbiodinium part,this recognition activity may be the premise of the symbiosis establishment.For the pathogenic bacteria,it is the first safeguard of innate immunity in scleractinian coral P.damicornis.Both of the recognition activities are inhibited under high temperature?>30??,that means the host may not be able to maintain the symbiosis with Symbiodinium on the one side,and the decrease of the immunological function of P.damicornis may lead to the failure of the resistance of pathogenic bacteria infection on the other.The research of PdGLT-1 preliminarily reveals the function of Gal-Lectin in P.damicornis in symbiosis and immunity,and conduct further study on the functional mechanism of lectin under heat pressure,thus providing a different perspective to the phenomenon of coral bleaching under heat stress.It would not only provide theoretical basis on the protection and recovery of coral ecosystem.