Full-length transcriptome maps of reef-building coral illuminate the molecular basis of calcification, symbiosis, and circadian genes

We sequenced the full-length transcriptomes of four common and frequently dominant reef-building corals, including two Robusta clade species, <i>Pocillopora damicornis</i> and <i>Pocillopora verrucosa</i>, and two Complexa clade species, <i>Acropora muricata</i> and <i>Montipora foliosa</i><i>,</i> using the PacBio Sequel II platform. We obtained information on gene functions, structures and expression profiles. Among them, a comparative analysis of biomineralization-related genes provided insights into the molecular basis of coral skeletal density. The gene expression profiles of the symbiote Symbiodiniaceae were also isolated and annotated from the holobiont sequence data; these profiles showed more highly convergent traits related to gene structure and expression level than those of coral hosts. Interestingly, we observed that intracellular algal cells share some evolutionary convergence between intracellular symbiosis in corals and intracellular digestion in amphioxus. Finally, a phylogenetic analysis of key circadian clock genes among 27 evolutionarily representative species indicated that there are four key members in early metazoans, including <i>cry </i>genes; <i>Clock</i> or <i>Npas2</i>; <i>cyc</i> or <i>Arntl</i>; and <i>tim</i>, while <i>per</i>, as the fifth member, occurs in Bilateria.