SUMO and SUMO-Conjugating Enzyme E2 UBC9 Are Involved in White Spot Syndrome Virus Infection in Fenneropenaeus chinensis

In previous work, small ubiquitin-like modifier (SUMO) in hemocytes of Chinese shrimp Fenneropenaeus chinensis was found to be up-regulated post-white spot syndrome virus (WSSV) infection using proteomic approach. However, the role of SUMO in viral infection is still unclear. In the present work, full length cDNAs of SUMO (FcSUMO) and SUMO-conjugating enzyme E2 UBC9 (FcUBC9) were cloned from F. chinensis using rapid amplification of cDNA ends approach. The open reading frame (ORF) of FcSUMO encoded a 93 amino acids peptide with the predicted molecular weight (M.W) of 10.55 kDa, and the UBC9 ORF encoded a 160 amino acids peptide with the predicted M.W of 18.35 kDa. By quantitative real-time RT-PCR, higher mRNA transcription levels of FcSUMO and FcUBC9 were detected in hemocytes and ovary of F. chinensis, and the two genes were significantly up-regulated post WSSV infection. Subsequently, the recombinant proteins of FcSUMO and FcUBC9 were expressed in Escherichia coli BL21 (DE3), and employed as immunogens for the production of polyclonal antibody (PAb). Indirect immunofluorescence assay revealed that the FcSUMO and UBC9 proteins were mainly located in the hemocytes nuclei. By western blotting, a 13.5 kDa protein and a 18.7 kDa protein in hemocytes were recognized by the PAb against SUMO or UBC9 respectively. Furthermore, gene silencing of FcSUMO and FcUBC9 were performed using RNA interference, and the results showed that the number of WSSV copies and the viral gene expressions were inhibited by knockdown of either SUMO or UBC9, and the mortalities of shrimp were also reduced. These results indicated that FcSUMO and FcUBC9 played important roles in WSSV infection.