Transcriptome Sequencing Reveals the Response to Acute Thermal Stress in the Pacific Abalone, Haliotis discus hannai

The Pacific abalone is an economically important cold-water shellfish. With its widespread culture, high temperature has become a key abiotic factor for the high mortality of Pacific abalone in summer, particularly in the south of China. To understand the molecular regulatory mechanisms of thermal stress response in Pacific abalone for further analyzing its heat adaptive capacity, we subjected Pacific abalone to acute heat stress at 28°C for 6, 24, and 48 hr, respectively. A total of 2,213, 2,337, and 1,420 differentially expressed genes (DEGs) were identified in Pacific abalone after 6, 24, and 48 hr of thermal stress, respectively, as compared with the control group without heat stimulation. These DEGs were significantly enriched in protein folding and chaperone-mediated protein folding process, antigen processing and presentation, and protein processing in endoplasmic reticulum pathways. The expression of numerous molecular chaperones was significantly upregulated after thermal stress. Maintaining cellular homeostasis through the upregulated expression of molecular chaperones associated with endoplasmic reticulum-associated degradation (ERAD) pathways might be central to the defense of Pacific abalone against thermal stress. In addition, the expression of Toll-like receptor 6 (TLR6) and myeloid differentiation factor 88 (MyD88) genes of the TLR signaling pathway was also induced. Therefore, the Pacific abalone might activate the immune defense system to resist the invasion of pathogenic bacteria by upregulating immune-related genes after thermal challenges. Our results not only contribute to a deeper understanding of heat stress regulation in the Pacific abalone but also provide basic data for molecular genetic breeding of heat-resistant abalone.