Characterization of Domeless receptors and the role of Bd Domeless3 in anti-symbiont-like virus defense in Bactrocera dorsalis

The Janus kinase/signal transducers and activators of transcription(JAK/STAT)signaling pathway play a pivotal role in innate immunity.Among invertebrates,Domeless receptors serve as the key upstream regulators of this pathway.In our study on Bactrocera dorsalis,we identified three cytokine receptors:BdDomeless1,BdDomeless2,and BdDomeless3.Each receptor encompasses five fibronectin-type-III-like(FN III)extracellular domains and a transmembrane domain.Furthermore,these receptors exhibit the increased responsiveness to diverse pathogenic challenges.Notably,only BdDomeless3 is upregulated during symbiont-like viral infections.Moreover,silencing BdDomeless3 enhanced the infectivity of Bactrocera dorsalis cripavirus(BdCV)and B.dorsalis picorna-like virus(BdPLV),underscoring BdDomeless3’s crucial role in antiviral defense of B.dorsalis.Following the suppression of Domeless3 expression,six antimicrobial peptide genes displayed decreased expression,potentially correlating with the rise in viral infectivity.To our knowledge,this is the first study identifying cytokine receptors associated with the JAK/STAT pathway in tephritid flies,shedding light on the immune mechanisms of B.dorsalis.

RNA interference in insects:the link between antiviral defense and pest control

RNA interference(RNAi)is a form of gene silencing triggered by double-stranded RNA(dsRNA)that operates in all eukaryotic cells.RNAi has been widely investigated in insects to determine the underlying molecular mechanism,to investigate its role in systemic antiviral defense,and to develop strategies for pest control.When insect cells are infected by viruses,viral dsRNA signatures trigger a local RNAi response to block viral replication and generate virus-derived DNA that confers systemic immunity.RNAi-based insect pest control involves the application of exogenous dsRNA targeting genes essential for insect development or survival,but the efficacy of this approach has limited potency in many pests through a combination of rapid dsRNA degradation,inefficient dsRNA uptake/processing,and ineffective RNAi machinery.This could be addressed by dsRNA screening and evaluation,focusing on dsRNA design and off-target management,as well as dsRNA production and delivery.This review summarizes recent progress to determine the role of RNAi in antiviral defense and as a pest control strategy in insects,addressing gaps between our fundamental understanding of the RNAi mechanism and the exploitation of RNAi-based pest control strategies.

Insect-specific RNA virus affects the stylet penetration activity of brown citrus aphid(Aphis citricidus)to facilitate its transmission

Sap-sucking insects often transmit plant viruses but also carry insect viruses,which infect insects but not plants.The impact of such insect viruses on insect host biology and ecology is largely unknown.Here,we identified a novel insect-specific virus carried by brown citrus aphid(Aphis citricidus),which we tentatively named Aphis citricidus picornavirus(AcPV).Phylogenetic analysis discovered a monophyletic cluster with AcPV and other unassigned viruses,suggesting that these viruses represent a new family in order Picornavirales.Systemic infection with AcPV triggered aphid antiviral immunity mediated by RNA interference,resulting in asymptomatic tolerance.Importantly,we found that AcPV was transmitted horizontally by secretion of the salivary gland into the feeding sites of plants.AcPV influenced aphid stylet behavior during feeding and increased the time required for intercellular penetration,thus promoting its transmission among aphids with plants as an intermediate site.The gene expression results suggested that this mechanism was linked with transcription of salivary protein genes and plant defense hormone signaling.Together,our results show that the horizontal transmission of AcPV in brown citrus aphids evolved in a manner similar to that of the circulative transmission of plant viruses by insect vectors,thus providing a new ecological perspective on the activity of insect-specific viruses found in aphids and improving the understanding of insect virus ecology.

The involvement of systemic RNA interference deficient-1-like (SIL1) in cellular dsRNA uptake in Acyrthosiphon pisum

Systemic RNA interference deficient-1-like(SIL1)is considered a core component in dsRNA uptake in some insect species.Investigation related to the potential function of SIL1 in dsRNA uptake can contribute to a further understanding of RNA interference(RNAi)mechanisms in insects and agricultural pest control.However,the role of SIL1 in dsRNA uptake in insects such as aphids remains controversial.We have thoroughly analyzed the role of SIL1 from the model aphid Acyrthosiphon pisum(ApSIL1)in cellular dsRNA to clarify its function.First,the induced expression of ApSIL1 upon dsRNA oral exposure provided a vital clue for the possible involvement of ApSIL1 in cellular dsRNA uptake.Subsequent in vivo experiments using the RNAi-of-RNAi approach for ApSIL1 supported our hypothesis that the silencing efficiencies of reporter genes were reduced after inhibition of ApSIL1 expression.The impaired biological phenotypes of aphids,including cumulative average offspring,deformities of the nymph,and mortality upon pathogen infection,were then observed in the treatment group.Thereafter,in vitro dual-luciferase reporter assay showed compelling evidence that the luciferin signal was significantly attenuated when dsluciferase or dsGFP was transferred into ApSIL1-transfected Drosophila S2 cells.These observations further confirmed that the signal of Cy3-labeled dsRNA was rapidly attenuated with time in ApSIL1-transfected Drosophila S2 cells.Overall,these findings conclusively establish that ApSIL1 is involved in dsRNA uptake in A.pisum.

GARP: A family of glycine and alanine-rich proteins that helps spider mites feed on plants

Spider mites(Tetranychidae)are destructive agricultural pests which have evolved strategies to overcome plant defenses,such as the ability to puncture the leaves of their hosts to feed.The expression of many genes with unknown functions is altered during feeding,but little is known about the role of these genes in plant–mite interactions.Here,we identified 3 novel gene families through analysis of genomic and transcriptomic data from 3 spider mite species.These GARP family genes encode glycine and alanine-rich proteins;they are present in mites(Acariformes)but absent in ticks(Parasitiformes)in the subclass Acari,indicating that these genes have undergone a significant expansion in spider mites and thus play important adaptive roles.Transcriptomic analysis revealed that the expression of GARP genes is strongly correlated with feeding and the transfer to new hosts.We used RNA interference to silence GARP1d in the two-spotted spider mite Tetranychus urticae,which inhibited feeding and egg laying and significantly increased mortality when the mites were transferred to soybean shoots;a similar effect was observed after TuVATPase was silenced.However,no changes in mite mortality were observed after TuGARP1d-silenced mites were placed on an artificial diet,which was different from the effect of TuVATPase silencing.Our results indicate that GARP family members play important roles in mite–plant interactions.Additional studies are needed to clarify the mechanisms underlying these interactions.

Discovery of a widespread presence bunyavirus that may have symbiont-like relationships with different species of aphids

Aphids are important agricultural pests,vectors of many plant viruses and have sophisticated relationships with symbiotic microorganisms.Abundant asymptomatic RNA viruses have been reported in aphids due to the application of RNA-seq,but aphid-virus interactions remain unclear.Bunyavirales is the most abundant RNA virus order,which can infect mammals,arthropods,and plants.However,many bunyaviruses have specific hosts,such as insects.Here,we discovered 18 viruses from 10 aphid species by RNA-seq.Importantly,a widespread presence bunyavirus,Aphid bunyavirus 1(ABV-1),was determined to have a wide host range,infecting and replicating in all 10 tested aphid species.ABV-1 may be transmitted horizontally during feeding on plant leaves and vertically through reproduction.In a comparison of the physiological parameters of ABV-1high and ABV-1low strains of pea aphid,higher ABV-1 titers reduced the total nymphal duration and induced the reproduction.Moreover,viral titer significantly affected the lipid and protein contents in pea aphids.In summary,we proposed that ABV-1 may have stable symbiont-like relationships with aphids,and these observations may provide a new direction for studying bunyaviruses in aphids and establishing a model for virus-aphid interactions.