Abstract
The increasing threat of ocean warming has led to the more frequent endangerment of coral reefs, including the heat-tolerant Pavona decussata. To shed light on the molecular mechanisms involved in the response of coral to ocean warming, we investigated the gene expression profiles of P. decussata after natural thermal stress. Using PacBio Sequel II sequencing technology, we obtained relatively complete transcriptome data for P. decussata and then analyzed its gene expression quantitatively with Illumina RNAseq technology. We acquired information on gene function, structure, and expression profile from coral host and zooxanthellae. Analysis of Illumina sequencing data revealed that unbleached coral host might rely on the active utilization of amino acids to maintain a stable living condition based on the tricarboxylic acid cycle under high temperature stress, and that zooxanthellae might benefit from ammonium produced by coral host. Moreover, the downregulation of unbleached coral host gene expression in innate immune pathways centered on the transcription factors that heat shock factor and nuclear factor (NF)-κB, as well as the tyrosine kinase pathway, might be crucial for maintaining the equilibrium of the zooxanthellae under thermal stress. Thus, the differences in these molecular mechanisms could determine, to some extent, whether coral host can maintain a symbiotic relationship with algae under heat stress. This study elucidated the molecular mechanisms underlying differences in thermal tolerance within P. decussata species and supported further theoretical basis in coral molecular biology and ecological conservation, which enhance our comprehension of coral responses to future climate change.