Structure and Function Analyses of the Thioredoxin 2 and Thioredoxin Reductase Gene in Pacific White Shrimp (Litopenaeus vannamei)

The thioredoxin (Trx) system is one of the most significant systems in living organisms as it regulates cellular redox reactions and plays a pivotal protective role within the cell by promoting redox homeostasis. <i>Trx</i> and thioredoxin reductase (<i>TrxR</i>) are the core oxidoreductases of the Trx system. In this study, the novel full-length cDNAs of <i>LvTrx2</i> and <i>LvTrxR</i> were cloned from <i>Litopenaeus vannamei</i>. The ORFs of <i>LvTrx2</i> and <i>LvTrxR</i> were 453 bp and 1785 bp, encoding polypeptides consisting of 150 and 596 amino acids. Sequence alignment analysis revealed that the amino acid sequence of <i>LvTrx2</i> shared a high degree of identity (93%) with that of <i>Penaeus chinensis</i>, while in <i>LvTrxR</i>, it exhibited a similarity level of 95% with previously submitted <i>Penaeus chinensis</i> and <i>Penaeus monodon</i> sequences. Regarding tissue-specific expression patterns, <i>LvTrx2</i> showed its highest expression levels in hepatopancreas and gill. For <i>LvTrxR</i>, the highest expression was observed in gill followed by hepatopancreas and intestine. During exposure to ammonia-N, there was a significant upregulation in the relative mRNA levels of <i>LvTrx2</i> and <i>LvTrxR</i> in hepatopancreas and gill, with the peak values occurring at 24 h or 48 h of exposure. After LPS injection, the <i>LvTrx2</i> and <i>LvTrxR</i> transcripts in hepatopancreas and gill had different upregulated levels. These findings suggest that <i>LvTrx2</i> and <i>LvTrxR</i> play pivotal roles in enhancing stress resistance and bolstering antibacterial defense mechanisms in <i>L. vannamei</i>. To explore the roles, <i>LvTrx2</i> expression was knocked down in vivo to verify the defense mechanism against 4-NP stress. <i>LvTrx2</i> silencing in 4-NP-challenged shrimp could significantly induce the gene expression of antioxidant-related genes (except for <i>LvTrxR</i>) and aggravate the oxidative damage of lipids. This study suggests that the Trx system is involved in regulating the antioxidant processes, and <i>LvTrx2</i> and <i>LvTrxR</i> play a vital role in defense responses against environmental stress.