The Effect of a Small Conotoxin-Like ctx Gene from Autographa californica Nuclear Polyhedrosis Virus (AcMNPV) on Insect Hemolymph Melanization

Abstract

The conotoxin-like (ctx) gene encodes a small cysteine-rich polypeptide in various baculoviruses. Previous research has demonstrated that the product of the ctx gene could be purified from insect cells infected by Autographa californica nuclear polyhedrosis virus (AcMNPV), but its function was unknown. In this paper, we compared the conserved cysteine motif structure (CX3GX2CX5CCX3CX6C) of the ctx gene in baculoviruses and generated recombinant Bombyx mori nuclear polyhedrosis virus (BmNPV) with the BmNPV bacmid system. The recombinant BmNPV contained the ctx gene from AcMNPV or a fusion gene of ctx with eGFP, respectively. Fluorescence in CTX-eGFP-positive cells was mainly observed on the cell membrane. To gain insight into CTX function, two methods were used to elucidate the affect CTX had on hemolymph melanization in vivo and in vitro in insect larvae and pupae. The results indicated that CTX abrogates hemolymph melanization; however, the mechanisms require further evaluation.

Immunity of an insect herbivore to an entomovirus is affected by different host plants

“…Virus infection generally triggers the immune reaction of host insects, specifically, a melanization response . Several studies found that virus infection led to decreased melanization, which is consistent with the results of this study. Moreover, we found the highest melanization rate in caterpillars fed I. aquatica and the lowest in those fed G. max , which implied that NPV‐infected caterpillars had stronger resistance and immunity against NPV infection when they consumed I. aquatica versus the other two plants.…”

“…For instance, the melanization response of the mosquito Armigeres subalbatus to a double subgenomic Sindbis (dsSIN) recombinant virus can be almost completely suppressed by the virus . A similar result was found for melanization of silkworm caterpillars ( Bombyx mori ) infected by nucleopolyhedrovirus (NPV), in which the hemolymph melanin of the caterpillars decreased . However, how host plants affect the melanization defense of insect herbivores infected by an entomovirus is not clear.…”

“…17 A similar result was found for melanization of silkworm caterpillars (Bombyx mori) infected by nucleopolyhedrovirus (NPV), in which the hemolymph melanin of the caterpillars decreased. 18 However, how host plants affect the melanization defense of insect herbivores infected by an entomovirus is not clear. Phenoloxidase (PO), dopa decarboxylase (DDC) and tyrosine hydroxylase (TH) are three of the most important melanization enzymes.…”

Cross-talking between baculoviruses and host insects towards a successful infection

“…Interestingly, a serpin orthologue has been found in the genome of a baculovirus, which exhibited inhibitory effects to a subset of host serine proteases, including those possibly involved in the melanization pathway [41]. A viral conotoxin-like gene encodes a small cysteine-rich polypeptide abrogates insect haemolymph melanization with unknown mechanisms [42].…”