WSV056 Inhibits Shrimp Nitric Oxide Synthase Activity by Downregulating Litopenaeus vannamei Sepiapterin Reductase to Promote White Spot Syndrome Virus Replication.

Wei Wang,Changkun Pan,Jianming Chen,Chen Yu,Peng Luo,Qin Zheng

doi:10.3389/fmicb.2021.796049

Abstract

Sepiapterin reductase (Spr) plays an essential role in the biosynthesis of tetrahydrobiopterin (BH4), a key cofactor of multiple enzymes involved in various physiological and immune processes. Suppression of Spr could result in BH4 deficiency-caused diseases in human and murine models. However, information on the biological function of Spr in invertebrates is limited. In this study, two Sprs (CG12116 and Sptr) from Drosophila melanogaster were found to be downregulated in transgenic flies overexpressing white spot syndrome virus (WSSV) immediate-early protein WSV056. CG12116 and Sptr exerted an inhibitory effect on the replication of the Drosophila C virus. A Litopenaeus vannamei Spr (LvSpr) exhibiting similarity of 64.1–67.5% and 57.3–62.2% to that of invertebrate and vertebrate Sprs, respectively, were cloned. L. vannamei challenged with WSSV revealed a significant decrease in LvSpr transcription and Spr activity in hemocytes. In addition, the BH4 co-factored nitric oxide synthase (Nos) activity in shrimp hemocytes was reduced in WSSV-infected and LvSpr knockdown shrimp, suggesting WSSV probably inhibits the LvNos activity through LvSpr downregulation to limit the production of nitric oxide (NO). Knockdown of LvSpr and LvNos caused the reduction in NO level in hemocytes and the increase of viral copy numbers in WSSV-infected shrimp. Supplementation of NO donor DETA/NO or double gene knockdown of WSV056 + LvSpr and WSV056 + LvNos recovered the NO production, whereas the WSSV copy numbers were decreased. Altogether, the findings demonstrated that LvSpr and LvNos could potentially inhibit WSSV. In turn, the virus has evolved to attenuate NO production via LvSpr suppression by WSV056, allowing evasion of host antiviral response to ensure efficient replication.

Highlights

Litopenaeus vannamei is the most abundant shrimp species in the world
nitric oxide synthase (Nos) significant difference was observed in the gene expression levels in the y, w group and UAS-wsv056-mCherry/da-Gal4, tub-Gal80ts group without a temperature-shift program
The results showed that endogenous Sptr and CG12116 in da-GAL4/Vienna Drosophila Resource Center (VDRC) 17017 and da-GAL4/VDRC 6498 flies significantly decreased compared with those in the control strain (Figure 1E), confirming the RNA interference (RNAi) construct effectively knocked down Sptr and CG12116

Summary

Introduction

Litopenaeus vannamei (white leg shrimp) is the most abundant shrimp species in the world. The increase in largescale intensive aquaculture systems and severe pollution of the environment has led to outbreaks of diseases caused by various pathogens. White spot syndrome virus (WSSV) is considered the most destructive pathogen in shrimp, leading to huge economic losses to the shrimp farming industry (Dey et al, 2020). White spot syndrome virus is enveloped, rod-shaped, and approximately 250 × 100 nm in size. The virus could infect a wide range of hosts, and it was found to contaminate a large population of wild marine crustaceans (Xu et al, 2021), enabling the easy spread of WSSV to aquaculture species and new geographical locations. No effective treatment is available to restrict the disease

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