Transcriptomic Analysis of Tachypleus tridentatus Larval Response to Vibrio parahaemolyticus Infection

<i>Tachypleus tridentatus</i> is a rare and endangered marine organism with considerable scientific and economic value. It has existed on Earth for about 450 million years and its continuation to the present day may be related to its unique immune system. Owing to its drastic population decline, diverse technical approaches are required for its recovery, and the development and growth of its larvae are crucial in this context. <i>Vibrio parahaemolyticus</i> is a common marine pathogen that impairs the healthy growth of marine organisms. The peak period of <i>V. parahaemolyticus</i> occurrence is from May to November, which significantly overlaps with the <i>T. tridentatus</i> spawning period from April to September. However, the response mechanisms of juvenile <i>T. tridentatus</i> to <i>V. parahaemolyticus</i> stress remain unknown. Hence, in this study, we aimed to investigate these response mechanisms through acute toxicity assays, histological observations, and transcriptome analysis. The results showed that the 48 h LD₅₀ of <i>V. parahaemolyticus</i>-infected <i>T. tridentatus</i> larvae was determined to be 1.31 × 10⁸ CFU/g. Histological analysis showed that <i>V. parahaemolyticus</i> damaged the larval tissue. In addition, RNA sequencing (RNA-Seq) identified 2347 differentially expressed genes (DEGs; 1440 upregulated and 907 downregulated genes) and 243 enriched signaling pathways. Functional enrichment analysis revealed the enrichment of immunoregulatory pathways, including the Wnt signaling pathway, ECM-receptor interaction, aminoacyl-tRNA biosynthesis, and Toll and Imd signaling pathways. Seventeen DEGs were randomly selected for real-time RT-PCR (RT-qPCR) validation, and their expression patterns were consistent with those obtained via RNA-Seq. The study of the response mechanism of <i>T. tridentatus</i> larvae to <i>V. parahaemolyticus</i> stress provides scientific references for the protection of <i>T. tridentatus</i> habitats and the recovery of its population size.