Baculovirus-mediated expression of a Chinese scorpion neurotoxin improves insecticidal efficacy

Regulation analysis of AcMNPV-mediated expression of a Chinese scorpion neurotoxin under the IE1, P10 and PH promoter in vivo and its use as a potential bio-insecticide

OBJECTIVE

To analyze the regulation mechanism of AcMNPV (Autographa californica multicapsid nucleopolyhedrovirus)-mediated expression of BmK IT under IE1, P10 and PH promoters in the larva of Heliothis armigera..

RESULTS

The transcription level of BmK IT gene in midgut and epidermal tissue was analyzed by quantitative PCR. The start time of transcription of recombinant BmK IT gene was early under the regulation of IE promoter, whereas transcription of BmK IT was high under the regulation of P10 promoter in the midgut tissue of infected larvae. TdT-UTP nick-end labeling (TUNEL) assay showed the degree of apoptotic cell death in the midgut tissue of AcMNPV-BmK IT-transfected insect larvae was higher than that in the AcMNPV treatment group at 8 h post-infection. The time-effect relationship between the insect's humoral immunity and regulation of promoters was confirmed in the phenoloxidase activity assay.

CONCLUSION

The anti-insect mechanism and regulation of different promoters in AcMNPV-BmK IT at molecular and cellular levels provide an experimental basis for the development of recombinant baculovirus biopesticides.

Expression, delivery and function of insecticidal proteins expressed by recombinant baculoviruses

Since the development of methods for inserting and expressing genes in baculoviruses, a line of research has focused on developing recombinant baculoviruses that express insecticidal peptides and proteins. These recombinant viruses have been engineered with the goal of improving their pesticidal potential by shortening the time required for infection to kill or incapacitate insect pests and reducing the quantity of crop damage as a consequence. A wide variety of neurotoxic peptides, proteins that regulate insect physiology, degradative enzymes, and other potentially insecticidal proteins have been evaluated for their capacity to reduce the survival time of baculovirus-infected lepidopteran host larvae. Researchers have investigated the factors involved in the efficient expression and delivery of baculovirus-encoded insecticidal peptides and proteins, with much effort dedicated to identifying ideal promoters for driving transcription and signal peptides that mediate secretion of the expressed target protein. Other factors, particularly translational efficiency of transcripts derived from recombinant insecticidal genes and post-translational folding and processing of insecticidal proteins, remain relatively unexplored. The discovery of RNA interference as a gene-specific regulation mechanism offers a new approach for improvement of baculovirus biopesticidal efficacy through genetic modification.

Scorpion peptide LqhIT2 activates phenylpropanoid pathways via jasmonate to increase rice resistance to rice leafrollers

LqhIT2 is an insect-specific toxin peptide identified in Leiurus quinquestriatus hebraeus that can be toxic to lepidoptera pests. However, whether LqhIT2 induces insect resistance in rice, and how the LqhIT2 influences the biochemical metabolism of rice plants remains unknown. Here, purified LqhIT2-GST fusion protein had toxicity to rice leafrollers. Meanwhile, in vitro and field trials showed that LqhIT2 transgenic rice plants were less damaged by rice leafrollers compared to the wild type plants. Introducing LqhIT2 primed the elevated expression of lipoxygenase, a key component of the jasmonic acid biosynthetic pathway, together with enhanced linolenic acid, cis-(+)-12-oxophytodienoic acid, jasmonic acid, and jasmonic acid-isoleucine levels. In addition, phenylalanine ammonia-lyase, a key gene of the phenylpropanoid pathway, was up-regulated. Correspondingly, the contents of downstream products of the phenylpropanoid pathway such as flavonoids and lignins, were also increased in LqhIT2 transgenic plants. These changes were paralleled by decreased starch, glucose, and glucose-6-phosphate accumulation, the key metabolites of glycolysis pathway that supplies the raw material and intermediate carbon products for phenylpropanoids biosyntheses. These findings suggest that, in addition to its own toxicity against pests, LqhIT2 activate the phenylpropanoid pathway via jasmonate-mediated priming, which subsequently increases flavonoid and lignin content and improves insect resistance in rice.