Abstract
Melanization, an important defense response, plays a vital role in arthropod immunity. It is mediated by serine proteases (SPs) that convert the inactive prophenoloxidase (PPO) to active phenoloxidase (PO) and is tightly regulated by serine protease inhibitors (serpins) which belong to a well distributed superfamily in invertebrates, participating in immune mechanisms and other important physiological processes. Here, we investigated the Bmserpin2 gene which was identified from a transcriptome database in response to Bombyx mori nucleopolyhedrovirus (BmNPV) infection. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that Bmserpin2 was expressed in all tissues, with maximum expression in fat body. Upon BmNPV infection, the expression of Bmserpin2 was up-regulated in P50 (susceptible strain) and BC9 (resistant strain) in haemocytes, fat body and the midgut. However, up-regulation was delayed in BC9 (48 or 72 h), in contrast to P50 (24 h), after BmNPV infection. Meanwhile, Bmserpin2 could delay or inhibit melanization in silkworm haemolymph. Significant increased PO activity can be observed in Bmserpin2-depleted haemolymph under NPV infection. Furthermore, the viral genomic DNA copy number was decreased in Bmserpin2-depleted haemolymph. We conclude that Bmserpin2 is an inducible gene which might be involved in the regulation of PPO activation and suppressed melanization, and have a potential role in the innate immune system of B. mori.
Highlights
Bombyx mori is a well-known lepidopteran insect with a great economic value as a producer of silk
The tissue distribution and developmental stages of Bmserpin2 expression levels were analysed by Quantitative real-time polymerase chain reaction (qRT-polymerase chain reaction (PCR))
The results indicated that Bmserpin2 was transcribed in all tissues including the midgut, fat body, haemocytes, integument, Malpighian tubules and head and silk gland
Summary
Bombyx mori is a well-known lepidopteran insect with a great economic value as a producer of silk. B. mori is used in many studies as model insect in genetics and applied biotechnology [1]. Bombyx mori nucleopolyhedrovirus (BmNPV) is a major burden for silkworms that causes serious loss to the sericulture industry. BmNPV contains two types of virion phenotypes, budded virus (BV). BV transfects cell-to-cell, while ODV spreads from one host to another host [2]. Most B. mori strains are highly susceptible to BmNPV, while only a few are highly resistant [3]. Studies on susceptible and resistant strains have increased the understanding of the mechanisms triggered by virus infection, a detailed understanding of B. mori resistance to
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