Cloning and characterization of tyrosine decarboxylase (TDC) from Litopenaeus vannamei, and its roles in biogenic amines synthesis, immune regulation, and resistance to Vibrio alginolyticus by RNA interference

The biogenic amines, tyramine and octopamine, in the octopaminergic synthesis pathway play critical roles in regulating physiological and immunological homeostasis in Litopenaeus vannamei. Tyrosine decarboxylase (TDC) is an enzyme catalyzing the first decarboxylation step in the biosynthesis of tyramine and octopamine. The fulllength gene sequence of TDC cloned from the brain of L. vannamei (LvTDC) was predicted to encode a 779-amino acid protein with a pyridoxal-dependent decarboxylase-conserved domain in close phylogenetic relationship with arthropod TDCs. LvTDC gene expression was found to be abundant in nervous thoracic ganglia. RNA interference was used to assess the immune and physiological function of LvTDC. The LvTDC knockdown shrimp revealed significant decreases in the total haemocyte count, hyaline cells, antimicrobial peptides, respiratory bursts, gene expression, respiratory bursts of haemocytes per unit of haemolymph, and phagocytic activity and clearance efficiency toward Vibrio alginolyticus. Furthermore, LvTDC knockdown was accompanied by decreases in octopamine deficiency. In the V. alginolyticus challenge test, the survival rate of LvTDC knockdown shrimp was lower than the shrimp injected with DEPC-water or GAPDH-dsRNA. In conclusion, the cloned LvTDC was responsible for octopaminergic synthesis, which then regulated physiological and immune responses in L. vannamei.

Automated summary

In Litopenaeus vannamei, the cloned LvTDC gene is responsible for the synthesis of octopamine, regulating physiological and immune responses. Knockdown of LvTDC resulted in significant decreases in immune function and physiological parameters, indicating the crucial role of LvTDC in maintaining homeostasis in shrimp.LvTDC knockdown shrimp also showed reduced survival rates in a Vibrio alginolyticus challenge test compared to control groups.