Physiological and molecular responses of Urechis unicinctus to high temperature stress (2)

The frequent occurrence of marine thermal wave events has caused serious harm to the growth and survival of marine organisms. Therefore, it is of great significance to explore the physiological and adaptation strategies of marine and coastal aquatic organisms in response to the high temperature stress. Urechis unicinctus is an important marine economic echiuran worm burrowing in coastal sediment. In this study, we demonstrated significant differences in the tissue structure, physiological, and gene expression of U. unicinctus under high temperature stress among individuals. In the surviving worms, the CAT and T-SOD activities and T-AOC in the body wall was significantly increased than that in the dying worms; correspondingly, the tissue structure of the body wall in the survivors was only slightly damaged, while the epithelial cells disintegrated and the mastoids disappeared in dying worms, suggesting that the antioxidant system may play an important role in U. unicincuts response and tolerance to the high temperature stress. Transcriptome analysis revealed that antioxidant defense, apoptosis, DNA damage, immune inflammation and hypoxia responses were the main differential pathways in response to high temperature stress between surviving and dying U. unicinctus. Our findings provide insights for further elucidating the response mechanisms of U. unicinctus to high temperature and the future application in the genetic improvement of high temperature tolerance traits.