Transcriptome and Metabolome Analyses of Sea Cucumbers Apostichopus japonicus in Southern China During the Summer Aestivation Period

Aestivation is a common strategy of sea cucumbers (Apostichopus japonicus) in response to high-temperature conditions. Previous studies have individually investigated the immune and physiological alterations at the aestivation stage. However, these studies have not evaluated the relationship between immunity and physiology. In this study, we explored the transcriptome and metabolome of A. japonicus during the aestivation stage to study the relationship. The transcriptome analysis of dormant (aestivation) and revived A. japonicus generated 2368 differentially expressed genes, including 927 downregulated genes and 1441 upregulated genes. Based on Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses, the downregulated genes in the dormant group were found to be involved in DNA replication, RNA metabolic process, and protein metabolism, which results in the inhibition of motility, skeletal development, neural activity, cell proliferation, and development of A. japonicus. In contrast, the upregulated genes were found to be associated with fatty acid metabolism, carbohydrate hydrolysis, and phagocytosis. In the metabolome analysis, the downregulated metabolites were found to be associated with fatty acid metabolism, starch and sucrose metabolism, and TCA cycle. This indicates that dormant sea cucumbers consume reserved carbohydrates and fatty acids to maintain low levels of energy supply. The protein-protein interaction network analysis further revealed that carbohydrate hydrolysis promoted phagocytosis activity in the dormant group. This study provides new insights into potential molecular mechanisms of sea cucumber survival in high-temperature conditions, which is critical in aquaculture of sea cucumbers.