Activation of PmRelish from Penaeus monodon by yellow head virus

• The PmRelish expression was up-regulated upon YHV challenges.
• The expression of penaeidin5 was under the regulation of Imd pathway.
• Under PmRelish silencing, the shrimp were more susceptible to YHV infection.
• The PmRelish was activated in response to YHV infection.
• The Imd pathway responded to YHV infection.

Humoral innate immune response against pathogenic infection is partly responsible by the Imd pathway in which a transcription factor Relish relays the infection signals to the nuclei for the expression of antimicrobial proteins. A PmRelish gene which encoded a protein of 1195 amino acids was cloned. The PmRelish was constitutively expressed in all tissues tested and mostly up-regulated upon YHV infection. In hemocytes, the PmRelish expression was up-regulated upon Vibrio harveyi, yellow head virus (YHV) and white spot syndrome virus (WSSV) challenges. Using dsRNA silencing of PmRelish gene, it was shown that the expression of penaeidin5 but not anti-lipopolysaccharide factor ALFPm3, crustinPm1 and penaeidin3 was under the regulation of Imd pathway. Under PmRelish silencing, the shrimp were more susceptible to infection by YHV with the 50% survival rate reduced from about 72 h to 42 h. The PmRelish was detected in the cytoplasm of all the hemocytes from both uninfected and YHV-infected shrimp. The accumulation of activated PmRelish in the nuclei was not clearly observed but the activated PmRelish was detected in the YHV-infected hemocytes by Western blot analysis. Thus, the PmRelish and, hence, the Imd pathway respond to the YHV infection.