Serine protease Bm-SP142 was differentially expressed in resistant and susceptible Bombyx mori strains, involving in the defence response to viral infection.

Guohui Li,Zhaoyang Hu,Qi Tang,Lipeng Qiu,Qin Yao,Qian Zhou,Keping Chen,Yi Li

doi:10.1371/journal.pone.0175518

Abstract

Bm-SP142 is a 35 kDa protease in the silkworm, but its exact functions remain unknown. In this study, sequence alignment revealed that the His-Asp-Ser catalytic triad is embedded in the TAAHC-DIAL-GDSGGP sequence motif, establishing Bm-SP142 as a serine protease. Soluble recombinant GST-BmSP142 was expressed and purified, and serine protease activity was confirmed in vitro. RT-qPCR results indicated that Bm-SP142 was mainly expressed in the middle part of the silkworm midgut, and Bm-SP142 transcripts were significantly up-regulated at 24 hours post infection (hpi) in BmBDV-resistant strains (798) inoculated with BmBDV and BmNPV-resistant strains (NB) inoculated with BmNPV, but not in BmBDV-susceptible strains (306). Surprisingly, transcripts were significantly down-regulated at 12 hpi in BmNPV-susceptible strains (HuaBa 35) inoculated with BmNPV, compared with healthy silkworms. Recombinant BmNPV treated with purified Bm-SP142 effectively impaired its ability to infect BmN cells, and Bm-SP142 decreases the efficiency of BmNPV and BmBDV propagation in silkworms. Furthermore, overexpression of Bm-SP142 in BmN cells inhibited viral propagation.

Highlights

The silkworm is an economically important insect that is raised in developing countries such as China, India and Thailand for the production of silk, and the industry was valued at ~31 billion dollars in 2012 in China alone [1]
Total RNA was extracted from susceptible strain HuaBa 35 and B.mori nucleopolyhedrovirus (BmNPV)-resistant strain NB individuals, and the results indicated that BmSP142 transcripts were expressed at a high level in healthy BmNPV-susceptible strain HuaBa 35 silkworms at 12 h, but levels decreased sharply from 24 hpi to 96 hpi in BmNPV-infected HuaBa 35 individuals (Fig 5C)
There is a significant difference of the Bm-SP142 abundance (p

Summary

Introduction

The silkworm is an economically important insect that is raised in developing countries such as China, India and Thailand for the production of silk, and the industry was valued at ~31 billion dollars in 2012 in China alone [1]. The silkworm is regarded as a model insect of the Order Lepidoptera, due to its convenience for scientific research [2,3,4]. This species is prone to infection by B.mori densovirus (BmBDV) and B.mori nucleopolyhedrovirus (BmNPV), resulting in great losses in sericulture [5,6,7].

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Conclusion