The Binding Characteristics Of Lectin To Symbiodiniaceae In Pocillopora Damicornis

In recent years,large-scale coral bleaching events owing to the rise of surface seawater temperature have occurred frequently,and the coral reef ecosystem has been facing a serious crisis of degradation.When the extent or speed of marine heatwave exceeds the thermal resistance of reef-building corals and their symbiotic Symbiodiniaceae,coral will loss their symbiotic Symbiodiniaceae and/or the loss of their pigment,and the symbiotic relationship between the two begins to collapse,and corals will gradually be bleached.The stable symbiosis between reef-building corals and Symbiodiniaceae is vital to the survival of corals,but the mechanism for the establishment and maintenance of the symbiosis remains to be understood.In this study,we used modern biological methods such as gene cloning and western blotting to investigate the binding activity and difference of coral lectins in the scleractinian coral Pocillopora damicornis to different species of symbiotic Symbiodiniaceae,and further clarify the potential role and significance of lectins in mediating changes in the community structure of Symbiodiniaceae under high temperature.The recombinant protein of PdGLT-1 was expressed and purified,and its binding activity to five symbiotic Symbiodiniaceae was positively correlated with the concentration of Symbiodiniaceae.The r PdGLT-1 recombinant protein had the highest binding activity to Symbiodinium microadriaticum,Cladocinium goreaui and Fugacium kawagutii at 30°C,while the binding activities to Breviolum minutum,and Durusdinium trenchii were the highest at 20°C and 35°C,respectively.At 25°C,PdGLT-1 recombinant protein mainly bond to a small area on the surface of S.microadriaticum,B.minutum and D.trenchii,and to the entire outer surface of C.goreaui and F.kawagutii,with obvious agglutinating effect on F.kawagutii.In addition,the cDNA sequences of a malectin PdMLT-1 and a C type lectin PdC-Lectin were cloned from P.damicornis.After the expression and purification in vitro,the recombinant proteins of PdGLT-1,PdMLT-1 and PdC-Lectin were used to compare the binding activities to Symbiodiniaceae.The binding activity to S.microadriaticum were compared,it was found that the activity of PdGLT-1 and PdC-Lectin were basically the same,and significantly higher than that of PdMLT-1.In the binding study of B.minutum and C.goreaui,there were significant differences between the three kinds of lectins,in which PdGLT-1 had the highest binding activity,then PdC-Lectin and PdMLT-1were followed,successively.In the binding study of D.trenchii and F.kawagutii,there were significant differences between the three kinds of lectins,in which PdC-Lectin had the highest binding activity,then PdGLT-1 and PdMLT-1were followed,successively.The above results suggest that the galectin PdGLT-1 can specifically recognize five different species of Symbiodiniaceae,including S.microadriaticum,B.minutum,C.goreaui,D.trenchii and F.kawagutii.Lectins can specifically bind the surface glycoproteins of Symbiodiniaceae,and the binding is affected by temperature and their different binding site.This study revealed the binding characteristics of lectin to different Symbiodiniaceae in Pocillopora damicornis,preliminarily elucidated the dynamic change mechanism of symbiotic Symbiodiniaceae community structure under environmental stress.It also provided theoretical reference and practical guidance for changing the community structure of symbiotic Symbiodiniaceae and improving the environmental acclimatization of reef-building corals.