Full-Length Transcriptomics Reveal the Gene Expression Profiles of Reef-Building Coral Pocillopora damicornis and Symbiont Zooxanthellae

Since the last century, episodes of coral reef bleaching and mortality have occurred almost annually in tropical or subtropical seas. When the temperature exceeds the tolerant limit of a coral–zooxanthellae holobiont, it induces physiological stress and disrupts the vulnerable fine-tuned balance between the two partners, leading to bleaching. The gene expression profiles of a scleractinian coral and its symbiotic zooxanthellae can offer important information with which to decipher this balanced relationship at the functional level of genes. Here, we sequence a full-length transcriptome of a well-known, common and frequently dominant reef-building coral, Pocillopora damicornis, to acquire gene expression information for the coral–zooxanthellae holobiont. To this end, we identify 21,926 and 465 unique genes in the coral and algal symbiont, respectively, and examine the functional enrichment among these genes based on GO (gene ontology) terms and KEGG (the Kyoto Encyclopedia of Genes and Genomes) pathways. The results show that the zooxanthellae provide for their coral host through energy and nutrition metabolism by photosynthesis, and that both the coral host and zooxanthellae have an anti-stress molecular mechanism, though the two parties have independent abilities to survive in the short term. This work sheds light on the valuable gene expression profile of a coral–zooxanthellae holobiont and provides grounds for further molecular biological research to support ecological protection work.