Effects On The Imd Pathway Genes Expression And Non-specific Immunity Of Fenneropenaeus Chinensis And Exopalaemon Carinicauda By Vibrio Anguillarum

As the most economically valuable and widely cultured species in China,Fenneropenaeus chinensis and Exopalaemon carinicauda are widely distributed alonethe coast of China. However, with the scale enlargement of culturing, their culturingenvironment is deteriorating, their development have been seriously affected by thefrequent outbreak of viral and bacterial diseases. Intensive studies on shrimp immunemechanisms can provide a theoretical basis for designing effective disease-controllingstrategies and thus are beneficial to the sustainable development of shrimp cultureindustry. Invertebrates rely on innate immunity as the first line defense againstmicrobes. The crustacean’s immune system belongs to the non-specific immunesystem which can identify the foreign body by pattern recognition receptor(PRRs),andtransmit the signal to the nuclear transcription factor(NF-KB),induce somenon-specific immune factors (such as AMPs、LZM、SOD、PO、iNOS) to play theirantibacterial action. In Drosophila, the inducible antimicrobial peptides (AMPs) areregulated by the Toll and Imd pathways. These two pathways play important roles ininnate immunity. The Imd pathway mainly participates in innate signaling to activatethe expression of AMP genes which resist the Gram-negative bacterium in shrimp.The cloning of the Imd pathway related genes and the research of immune mechanismis helpful to resist some bacterial diseases in shrimp culture.According to the Imd and Relish genes cDNA sequence of relevant spieceswhich have already been submitted to GENEBANK, the core segments ofFenneropenaeus chinensis’s Imd gene and Exopalaemon carinicauda’s Relish geneare got. Then the technology of3’and5’RACE are used to get the two terminals. thefull-length cDNA of Imd gene in Fenneropenaeus chinensis is784bp with5’UTR of 45bp and3’UTR of256bp and an open reading frame of483bp that encodes aputative protein of160amino acids including a death domain at the C-terminus whichis roughly the same with the Litopenaeus vannamei,and show high similarity withthe IMD protein of Drosophila and human receptor interacting protein1(RIP1) ofthe tumor necrosis factor receptor pathway, with about27.9%and26.4%identity. Thefull length of Relish gene in Exopalaemon carinicauda is2141bp, exhibits31bp of5’UTR,127bp of3’ UTR and1983bp of the open reading frame encoding apolypeptide of660amino acids. The protein sequence includes a typical conservedcytosolic IPT domain which is typical to the NF-kB, and belongs to the RHD-nsuperfamily.In order to understand the disease resistance ability of the two shrimps, and thefunction of the Imd pathway genes in the two shrimps, the death counts wererecorded,and the expression of the Imd pathway genes were tested by real-time PCRafter the two shrimps challenged by V. anguillarum. After challenged by bacteria,Fenneropenaeus chinensis mortality was faster than Exopalaemon carinicauda in theearly time, and the death rate of Fenneropenaeus chinensis became slowly, while thedeath rate of Exopalaemon carinicauda continued to rise at12hour post injection.The expressions of Imd pathway genes were all decreased compared with the controlgroup after challenged by V. anguillarum. But the expressions of Relish genegradually was restored to normal level. The non-specific immunity enzymeactivities(LZM,SOD,PO,iNOS) were increased more significantly to varying degreesand restored to normal until48h after injection. It wasn’t found a positive correlationbetween the non-specific immunity enzyme activities and the expressions of Relishgene. These results together indicated that the stress ability of Fenneropenaeuschinensis is worse than Exopalaemon carinicauda. Exopalaemon carinicauda canstart its immunologic defence rapidly compared with Fenneropenaeus chinensisfacing with bacterial invasion. Imd gene and Relish gene all play important roles inthe immune response of shrimps, and the reaction of Imd gene is stronger than Relishgene. Relish gene always maintain in appropriate level after challenged by somebacterium finally. Considering the response time of the immune factors in Exopalaemon carinicauda is longer than the Fenneropenaeus chinensis, so maybe thepremonition of Exopalaemon is stronger than Fenneropenaeus chinensis. The immunefunction of shrimps may rehabilitate to normal after infected by some bacterium,maybe the time is48hour after infected.