Members of the TRAF gene family in Octopus sinensis and their response to PGN, poly I:C, and Vibrio parahaemolyticus

Octopus sinensis, the species of Cephalopoda, is known as the highest Mollusca and is an economic and new aquaculture species in the coastal waters of southern China. The immune system has been well documented to have a function of resisting the invasion of pathogens in the external environment among mollusca species. As a kind of signaling molecule in the innate immune system, tumor necrosis factor (TNF) receptor-associated factor (TRAF) plays significant roles in TNF receptor (TNFR)/interleukin-1 receptor (IL-1R) /Toll-like receptor (TLR) signaling pathways. Until now, seven TRAF members (TRAF1-7) have been discovered, and they have been reported to participate in regulating signal pathways mediated by pattern recognition receptors and play important roles in the innate immune response of the hosts. In this study, five TRAF genes of O. sinensis (OsTRAF2, OsTRAF3, OsTRAF4, OsTRAF6, and OsTRAF7) were identified, whose full length of the open reading frame is 1473 bp, 1629 bp, 1431 bp, 1353 bp and 2121 bp respectively, encoding 490, 542, 476, 450 and 706 amino acids, respectively. Bioinformatics analysis showed that each OsTRAF has different chromosome locations. In addition to seven consecutive WD40 domains on the C-terminal of OsTRAF7 protein, the C-terminal of OsTRAF proteins all contain a conserved TRAF domain, namely the MATH domain. Phylogenetic analysis showed that OsTRAF proteins were clustered together with TRAF proteins of bivalves. Moreover, TRAF1 and TRAF2, TRAF3 and TRAF5 were clustered together in a large clade, respectively, revealing they have a close genetic relationship. The results of quantitative Real-time PCR showed that OsTRAF genes were highly expressed in the gill, hepatopancreas and white body. After stimulation with PGN, poly I:C and V. parahaemolyticus, the expression levels of OsTRAF genes were up-regulated in the gill, hepatopancreas and white body at different time points. These results indicated that OsTRAF genes play an important role in the antibacterial and antiviral immune response of O. sinensis.