Sequencing And Analysis Of Full-length Transcriptomes Of Reef-building Corals

Coral reefs are known as "tropical rainforests in the ocean",providing habitats for a large number of marine organisms.Reef-building corals,as their main components,play an important role in marine ecosystems.In recent decades,due to the effects of climate change,ocean acidification and other marine environmental degradation,and the predation of invasive long-thorn starfish,coral reef bleaching and death events have occurred frequently around the world.The massive decline of coral reefs has become a global scientific problem that needs to be solved urgently.When the external environmental stress exceeds the tolerance limit of the symbiont composed of coral and zooxanthellae,it will cause the imbalance of symbiotic relationship and the escape of zooxanthellae,which is manifested as coral bleaching.Once prolonged,coral bleaching cannot be reversed,resulting in coral death.At present,the research on the symbiotic mechanism of reef-building coral and its zooxanthellae is aimed at one of the species,and it is impossible to form an overall understanding of the gene expression,cell signaling pathway,and gene regulation network mechanism of reef-building coral symbionts.In this paper,the gene expression library construction,sequencing and analysis of the full-length transcriptomes of four representative reef-building corals,Pocillopora damicornis,Pocillopora verrucosa,Montipora capricornis and Acropora muricata,were performed for the first time in the South China Sea.We used Pacbio Sequel II third-generation sequencing technology for full-length transcriptome sequencing,and used Illumina second-generation high-throughput sequencing technology for data accuracy correction,and the sequencing accuracy reached more than 99.99%.We analyzed the common and differentially expressed genes of the four types of corals and their zooxanthellae,respectively,and enriched the signaling pathways involved in the related differential genes.We found that the correlation coefficient of gene expression in coral symbionts P.damicornis and P.verrucosa was over 0.6,and the correlation coefficient of zooxanthellae genes was over 0.9.The study showed that there were few differentially expressed genes screened in the four types of coral zooxanthellae,and their enriched signaling pathways were concentrated,and the gene expression profiles of the same species in reef-building corals were the most similar.The signal pathways enriched by the differentially expressed zooxanthellae genes in the four types of corals have a certain repeatability with the signal pathways enriched by the differential genes of corals,suggesting that the gene expression of zooxanthellae will change with the change of the gene expression of the host coral.Reef-building coral is a marine animal composed of polyps,and asexual budding reproduction is its main reproductive and developmental type.At present,the mechanism of budding growth in reef-building corals is still unclear.In this paper,for the first time,a comparative study of the fibroblast growth factor(FGF)-fibroblast growth factor receptor(FGFR)gene sequences that play a key role in the budding morphology of four coral species is carried out,and a three-dimensional(3D)model of the FGF and FGFR proteins is established.And the two docking models are reconstructed.It was found that the FGF8-FGFR3 binding model in P.damicornis,M.capricornis and A.muricata is a typical receptor tyrosine kinase signaling pathway,similar to Kringelchen(FGFR)in the hydra.In P.verrucosa,however,FGF8 is not a FGFR3 ligand,suggesting that its FGFR3 should be activated by other tyrosine kinase-type ligands.In this paper,the transcriptomes of four types of corals and their zooxanthellae in the South China Sea were analyzed in depth.From the perspective of gene expression,we have formed a comprehensive understanding of the physiological functions of reef-building corals,and provided a basis for the ecological protection of reef-building corals in the future.Important genomics foundations.At the same time,the paper analyzes for the first time the combination of FGF-FGFR signaling pathway of reef-building coral budding reproduction,which provides a molecular biology research approach and an important background for further reef-building coral protection.