CONTROL OF PROPHENOLOXIDASE SYSTEM AND ITS ROLE IN ANTIVIRAL IMMUNITY IN SHRIMP  

Pakkakul Sangsuriya*1,2, Walaiporn Charoensapsri, Sudarat Chomwong,
Saengchan Senapin, Anchalee Tassanakajon, and Piti Amparyup
 
1Aquatic Molecular Genetics and Biotechnology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency (NSTDA), Paholyothin Road, Pathumthani 12120, Thailand
2Center of Excellence for Molecular Biology and Genomics of Shrimp, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Phayathai Road, Bangkok 10330, Thailand
pakkakul.san@biotec.or.th

Melanization, activated by phenoloxidase (PO) and controlled by prophenoloxidase (proPO) system, is an essential innate immunity in invertebrates. Previously, our research group has been demonstrated a crucial role of melanization in shrimp defense against bacterial and fungal pathogens. However, its function against viral infection remains poorly understood. The present study aimed to characterize the mechanism of melanization to counteract a major viral pathogen White spot syndrome virus (WSSV) and to investigate the function of proPOs in controlling the melanization cascade in shrimp Penaeus monodon. First, through protein-protein interaction assays the viral protein WSV108 was identified to bind with PmproPO2 and showed the ability to inhibit PO activity. Gene silencing of WSV108 also showed a significant increase of PO activity in WSSV-infected shrimp suggesting that WSSV might interfere shrimp immune response through suppression of the proPO system. Second, the importance of proPOs in regulation of the proPO cascade was next investigated. By using suppression subtractive hybridization in the PmproPO1/2 co-silenced shrimp, a novel regulator of proPO system was then identified named as PmPacifastin-like gene, belonging to a new family of serine proteinase inhibitors. Gene silencing of PmPacifastin-like revealed its mechanism in control of proPO system in which suppression of PmPacifastin-like caused a significant increase of PO activity in knockdown shrimp. Interestingly, suppression of PmPacifastin-like gene also contributed to down-regulate the expression of a serine proteinase PmPPAE2 transcript. PmPacifastin-like was also found to be the immune responsive gene to bacteria Vibrio harveyi infection. In summary, the data from this study could enhance our understanding of the systemic regulation of proPO-related genes and provide insights into the antiviral immunity by the proPO system.