Polydnaviruses are a group of insect DNA viruses and are characterized in their segmented genome that is located in the chromosome（s） of host wasps. A polydnavirus, Cotesiaplutellae bracovirus （CpBV）, encodes a vi...Polydnaviruses are a group of insect DNA viruses and are characterized in their segmented genome that is located in the chromosome（s） of host wasps. A polydnavirus, Cotesiaplutellae bracovirus （CpBV）, encodes a viral ribonuclease （RNase） T2 in a specific segment #3 （CpBV-S3）. This study tested its effect on gene expression associated with host immune responses in the diamondback moth, Plutella xylostella. Micro-inj ection of CpBV- $3 into nonparasitized larvae induced expression of its two encoded genes, CpBV-ORF301 （= CpBV-RNase T2） and CpBV-ORF302. In response to a bacterial challenge, four antimi- crobial peptide genes （hemolin, gloverin, cecropin and lysozyme） and six phenoloxidase （PO）-associated genes （proPO-activating proteinase, PO, serine proteinase homolog and serpins 1-3） were up-regulated in their expressions. However, the transient expression of CpBV-S3 suppressed the expressions of cecropin, PO and serpin 1. Double-stranded RNA specific to the viral RNase T2 could specifically knockdown the viral gene expression and restored the three gene expressions suppressed in the larvae injected with CpBV-S3. The inhibitory activity of the viral RNase T2 on the target genes was further proven by the suppression of PO activation in response to bacterial challenge in the larvae injected with CpBV-S3. This immunosuppression by the expression of the viral RNase T2 resulted in significant increase of pathogen susceptibility ofP. xylostella against Bacillus thuringiensis or baculovirus infection.展开更多
Polydnaviruses(PDVs)are obligatory symbionts of parasitoid wasps and play an important role in suppressing host immune defenses.Although PDV genes that inhibit host melanization are known in Microplitis bracovirus,the...Polydnaviruses(PDVs)are obligatory symbionts of parasitoid wasps and play an important role in suppressing host immune defenses.Although PDV genes that inhibit host melanization are known in Microplitis bracovirus,the functional homologs in Cotesia bracoviruses remain unknown.Here,we find that Cotesia vestalis bracovirus(CvBV)can inhibit hemolymph melanization of its host,Plutella xylostella larvae,during the early stages of parasitization,and that overexpression of highly expressed CvBV genes reduced host phenoloxidase activity.Furthermore,CvBV-7-I in particular reduced host phenolox-idase activity within 12 h,and the injection of anti-CvBV-7-1 antibody increased the melanization of parasitized host larvae.Further analyses showed that CvBV-7-1 and three homologs from other Cotesia bracoviruses possessed a C-terminal leucine/isoleucine-rich region and had a similar flinction in inhibiting melanization.Therefore,a new family of bracovirus genes was proposed and named as C-terminal Leucine/isoleucine-rich Protein(CLP).Ectopic expression of CvBV-7-1 in Drosophila hemocytes increased susceptibility to bacterial repression of melanization and reduced the melanotic encapsulation of par-asitized D.melanogaster by the parasitoid Leptopilina boulardi.The formation rate of wasp pupae and the eclosion rate of C.vestalis were affected when the function of CvBV-7-1 was blocked.Our findings suggest that CLP genes from Cotesia bracoviruses encoded proteins that contain a C-terminal leucine/isoleucine-rich region and function as melanization inhibitors during the early stage of parasitization,which is important for successful parasitization.展开更多
文摘Polydnaviruses are a group of insect DNA viruses and are characterized in their segmented genome that is located in the chromosome（s） of host wasps. A polydnavirus, Cotesiaplutellae bracovirus （CpBV）, encodes a viral ribonuclease （RNase） T2 in a specific segment #3 （CpBV-S3）. This study tested its effect on gene expression associated with host immune responses in the diamondback moth, Plutella xylostella. Micro-inj ection of CpBV- $3 into nonparasitized larvae induced expression of its two encoded genes, CpBV-ORF301 （= CpBV-RNase T2） and CpBV-ORF302. In response to a bacterial challenge, four antimi- crobial peptide genes （hemolin, gloverin, cecropin and lysozyme） and six phenoloxidase （PO）-associated genes （proPO-activating proteinase, PO, serine proteinase homolog and serpins 1-3） were up-regulated in their expressions. However, the transient expression of CpBV-S3 suppressed the expressions of cecropin, PO and serpin 1. Double-stranded RNA specific to the viral RNase T2 could specifically knockdown the viral gene expression and restored the three gene expressions suppressed in the larvae injected with CpBV-S3. The inhibitory activity of the viral RNase T2 on the target genes was further proven by the suppression of PO activation in response to bacterial challenge in the larvae injected with CpBV-S3. This immunosuppression by the expression of the viral RNase T2 resulted in significant increase of pathogen susceptibility ofP. xylostella against Bacillus thuringiensis or baculovirus infection.
基金supported by the Key Program of National Natural Science Foundation of China(31630060)National Key Research and Development Program of China(2019YFD0300104)to XXC+5 种基金the National Key Research and Development Program of China(2017YFD0200400)the National Science Fund for Excellent Young Scholars(31622048)the National Science Foundation of China(31772522)to JHHthe National Science Foundation of China(31672079)Zhejiang Provincial Natural Science Foundation of China(LR18C140001)to MSthe National Science Foundation of China(31901942)to ZHW.
文摘Polydnaviruses(PDVs)are obligatory symbionts of parasitoid wasps and play an important role in suppressing host immune defenses.Although PDV genes that inhibit host melanization are known in Microplitis bracovirus,the functional homologs in Cotesia bracoviruses remain unknown.Here,we find that Cotesia vestalis bracovirus(CvBV)can inhibit hemolymph melanization of its host,Plutella xylostella larvae,during the early stages of parasitization,and that overexpression of highly expressed CvBV genes reduced host phenoloxidase activity.Furthermore,CvBV-7-I in particular reduced host phenolox-idase activity within 12 h,and the injection of anti-CvBV-7-1 antibody increased the melanization of parasitized host larvae.Further analyses showed that CvBV-7-1 and three homologs from other Cotesia bracoviruses possessed a C-terminal leucine/isoleucine-rich region and had a similar flinction in inhibiting melanization.Therefore,a new family of bracovirus genes was proposed and named as C-terminal Leucine/isoleucine-rich Protein(CLP).Ectopic expression of CvBV-7-1 in Drosophila hemocytes increased susceptibility to bacterial repression of melanization and reduced the melanotic encapsulation of par-asitized D.melanogaster by the parasitoid Leptopilina boulardi.The formation rate of wasp pupae and the eclosion rate of C.vestalis were affected when the function of CvBV-7-1 was blocked.Our findings suggest that CLP genes from Cotesia bracoviruses encoded proteins that contain a C-terminal leucine/isoleucine-rich region and function as melanization inhibitors during the early stage of parasitization,which is important for successful parasitization.
