Targeted disruption of aphid transmission: a vision for the management of crop diseases caused by Luteoviridae members

Aphid gene expression following polerovirus acquisition is host species dependent

Upon acquisition of persistent circulative viruses such as poleroviruses, the virus particles transcytose through membrane barriers of aphids at the midgut and salivary glands via hemolymph. Such intricate interactions can influence aphid behavior and fitness and induce associated gene expression in viruliferous aphids. Differential gene expression can be evaluated by omics approaches such as transcriptomics. Previously conducted aphid transcriptome studies used only one host species as the source of virus inoculum. Viruses typically have alternate hosts. Hence, it is not clear how alternate hosts infected with the same virus isolate alter gene expression in viruliferous vectors. To address the question, this study conducted a transcriptome analysis of viruliferous aphids that acquired the virus from different host species. A polerovirus, cotton leafroll dwarf virus (CLRDV), which induced gene expression in the cotton aphid, Aphis gossypii Glover, was assessed using four alternate hosts, viz., cotton, hibiscus, okra, and prickly sida. Among a total of 2,942 differentially expressed genes (DEGs), 750, 310, 1,193, and 689 genes were identified in A. gossypii that acquired CLRDV from infected cotton, hibiscus, okra, and prickly sida, respectively, compared with non-viruliferous aphids that developed on non-infected hosts. A higher proportion of aphid genes were overexpressed than underexpressed following CLRDV acquisition from cotton, hibiscus, and prickly sida. In contrast, more aphid genes were underexpressed than overexpressed following CLRDV acquisition from okra plants. Only four common DEGs (heat shock protein, juvenile hormone acid O-methyltransferase, and two unannotated genes) were identified among viruliferous aphids from four alternate hosts. Gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations indicated that the acquisition of CLRDV induced DEGs in aphids associated with virus infection, signal transduction, immune systems, and fitness. However, these induced changes were not consistent across four alternate hosts. These data indicate that alternate hosts could differentially influence gene expression in aphids and presumably aphid behavior and fitness despite being infected with the same virus isolate.

Appropriate reduction of importin-α gene expression enhances yellow dwarf disease resistance in common wheat

Barley yellow dwarf viruses (BYDVs) cause widespread damage to global cereal crops. Here we report a novel strategy for elevating resistance to BYDV infection. The 17K protein, a potent virulence factor conserved in BYDVs, interacted with barley IMP-α1 and -α2 proteins that are nuclear transport receptors. Consistently, a nuclear localization signal was predicted in 17K, which was found essential for 17K to be transported into the nucleus and to interact with IMP-α1 and -α2. Reducing HvIMP-α1 and -α2 expression by gene silencing attenuated BYDV-elicited dwarfism, accompanied by a lowered nuclear accumulation of 17K. Among the eight common wheat CRISPR mutants with two to four TaIMP-α1 and -α2 genes mutated, the triple mutant α1aaBBDD /α2AAbbdd and the tetra-mutant α1aabbdd /α2AAbbDD displayed strong BYDV resistance without negative effects on plant growth under field conditions. The BYDV resistance exhibited by α1aaBBDD /α2AAbbdd and α1aabbdd /α2AAbbDD was correlated with decreased nuclear accumulation of 17K and lowered viral proliferation in infected plants. Our work uncovers the function of host IMP-α proteins in BYDV pathogenesis and generates the germplasm valuable for breeding BYDV-resistant wheat. Appropriate reduction of IMP-α gene expression may be broadly useful for enhancing antiviral resistance in agricultural crops and other economically important organisms.

Polerovirus N-terminal readthrough domain structures reveal molecular strategies for mitigating virus transmission by aphids

Poleroviruses, enamoviruses, and luteoviruses are icosahedral, positive sense RNA viruses that cause economically important diseases in food and fiber crops. They are transmitted by phloem-feeding aphids in a circulative manner that involves the movement across and within insect tissues. The N-terminal portion of the viral readthrough domain (NRTD) has been implicated as a key determinant of aphid transmission in each of these genera. Here, we report crystal structures of the NRTDs from the poleroviruses turnip yellow virus (TuYV) and potato leafroll virus (PLRV) at 1.53-Å and 2.22-Å resolution, respectively. These adopt a two-domain arrangement with a unique interdigitated topology and form highly conserved dimers that are stabilized by a C-terminal peptide that is critical for proper folding. We demonstrate that the PLRV NRTD can act as an inhibitor of virus transmission and identify NRTD mutant variants that are lethal to aphids. Sequence conservation argues that enamovirus and luteovirus NRTDs will follow the same structural blueprint, which affords a biological approach to block the spread of these agricultural pathogens in a generalizable manner.

Complex and simple translational readthrough signals in pea enation mosaic virus 1 and potato leafroll virus, respectively

Different essential viral proteins are translated via programmed stop codon readthrough. Pea enation mosaic virus 1 (PEMV1) and potato leafroll virus (PLRV) are related positive-sense RNA plant viruses in the family Solemoviridae, and are type members of the Enamovirus and Polerovirus genera, respectively. Both use translational readthrough to express a C-terminally extended minor capsid protein (CP), termed CP-readthrough domain (CP-RTD), from a viral subgenomic mRNA that is transcribed during infections. Limited incorporation of CP-RTD subunits into virus particles is essential for aphid transmission, however the functional readthrough structures that mediate CP-RTD translation have not yet been defined. Through RNA solution structure probing, RNA secondary structure modeling, site-directed mutagenesis, and functional in vitro and in vivo analyses, we have investigated in detail the readthrough elements and complex structure involved in expression of CP-RTD in PEMV1, and assessed and deduced a comparatively simpler readthrough structure for PLRV. Collectively, this study has (i) generated the first higher-order RNA structural models for readthrough elements in an enamovirus and a polerovirus, (ii) revealed a stark contrast in the complexity of readthrough structures in these two related viruses, (iii) provided compelling experimental evidence for the strict requirement for long-distance RNA-RNA interactions in generating the active readthrough signals, (iv) uncovered what could be considered the most complex readthrough structure reported to date, that for PEMV1, and (v) proposed plausible assembly pathways for the formation of the elaborate PEMV1 and simple PLRV readthrough structures. These findings notably advance our understanding of this essential mode of gene expression in these agriculturally important plant viruses.

Yellow Dwarf Viruses of Cereals: Taxonomy and Molecular Mechanisms

Yellow dwarf viruses are the most economically important and widespread viruses of cereal crops. Although they share common biological properties such as phloem limitation and obligate aphid transmission, the replication machinery and associated cis-acting signals of these viruses fall into two unrelated taxa represented by Barley yellow dwarf virus and Cereal yellow dwarf virus. Here, we explain the reclassification of these viruses based on their very different genomes. We also provide an overview of viral protein functions and their interactions with the host and vector, replication mechanisms of viral and satellite RNAs, and the complex gene expression strategies. Throughout, we point out key unanswered questions in virus evolution, structural biology, and genome function and replication that, when answered, may ultimately provide new tools for virus management.

Barley GRIK1-SnRK1 kinases subvert a viral virulence protein to upregulate antiviral RNAi and inhibit infection

Viruses often usurp host machineries for their amplification, but it remains unclear if hosts may subvert virus proteins to regulate viral proliferation. Here, we show that the 17K protein, an important virulence factor conserved in barley yellow dwarf viruses (BYDVs) and related poleroviruses, is phosphorylated by host GRIK1‐SnRK1 kinases, with the phosphorylated 17K (P17K) capable of enhancing the abundance of virus‐derived small interfering RNAs (vsiRNAs) and thus antiviral RNAi. Furthermore, P17K interacts with barley small RNA‐degrading nuclease 1 (HvSDN1) and impedes HvSDN1‐catalyzed vsiRNA degradation. Additionally, P17K weakens the HvSDN1‐HvAGO1 interaction, thus hindering HvSDN1 from accessing and degrading HvAGO1‐carried vsiRNAs. Importantly, transgenic expression of 17K phosphomimetics (17K^5D), or genome editing of SDN1, generates stable resistance to BYDV through elevating vsiRNA abundance. These data validate a novel mechanism that enhances antiviral RNAi through host subversion of a viral virulence protein to inhibit SDN1‐catalyzed vsiRNA degradation and suggest new ways for engineering BYDV‐resistant crops.

Nanocarriers: A novel strategy for the delivery of CRISPR/Cas systems

In recent decades, clustered regularly interspaced short palindromic repeat/CRISPR-associated protein (CRISPR/Cas) has become one of the most promising genome-editing tools for therapeutic purposes in biomedical and medical applications. Although the CRISPR/Cas system has truly revolutionized the era of genome editing, the safe and effective delivery of CRISPR/Cas systems represents a substantial challenge that must be tackled to enable the next generation of genetic therapies. In addition, there are some challenges in the in vivo delivery to the targeted cells/tissues. Nanotechnology-based drug delivery systems can be employed to overcome this issue. This review discusses different types and forms of CRISPR/Cas systems and the current CRISPR/Cas delivery systems, including non-viral carriers such as liposomes, polymeric, and gold particles. The focus then turns to the viral nanocarriers which have been recently used as a nanocarrier for CRISPR/Cas delivery.

Transmission of Grapevine Red Blotch Virus by Spissistilus festinus [Say, 1830] (Hemiptera: Membracidae) between Free-Living Vines and Vitis vinifera 'Cabernet Franc'

Grapevine red blotch disease emerged within the past decade, disrupting North American vine stock production and vineyard profitability. Our understanding of how grapevine red blotch virus (GRBV), the causal agent of the disease, interacts with its Vitis hosts and insect vector, Spissistilus festinus, is limited. Here, we studied the capabilities of S. festinus to transmit GRBV from and to free-living vines, identified as first-generation hybrids of V. californica and V. vinifera ‘Sauvignon blanc’ (Vcal hybrids), and to and from V. vinifera ‘Cabernet franc’ (Vvin Cf) vines. The transmission rate of GRBV was high from infected Vcal hybrid vines to healthy Vcal hybrid vines (77%, 10 of 13) and from infected Vvin Cf vines to healthy Vcal hybrid vines (100%, 3 of 3). In contrast, the transmission rate of GRBV was low from infected Vcal hybrid vines to healthy Vvin Cf vines (15%, 2 of 13), and from infected Vvin Cf vines to healthy Vvin Cf vines (19%, 5 of 27). No association was found between transmission rates and GRBV titer in donor vines used in transmission assays, but the virus titer was higher in the recipient leaves of Vcal hybrid vines compared with recipient leaves of Vvin Cf vines. The transmission of GRBV from infected Vcal hybrid vines was also determined to be trans-stadial. Altogether, our findings revealed that free-living vines can be a source for the GRBV inoculum that is transmissible by S. festinus to other free-living vines and a wine grape cultivar, illustrating the interconnected roles of the two virus hosts in riparian areas and commercial vineyards, respectively, for virus spread. These new insights into red blotch disease epidemiology will inform the implementation of disease management strategies.

RNA Interference: Promising Approach to Combat Plant Viruses

Plant viruses are devastating plant pathogens that severely affect crop yield and quality. Plants have developed multiple lines of defense systems to combat viral infection. Gene silencing/RNA interference is the key defense system in plants that inhibits the virulence and multiplication of pathogens. The general mechanism of RNAi involves (i) the transcription and cleavage of dsRNA into small RNA molecules, such as microRNA (miRNA), or small interfering RNA (siRNA), (ii) the loading of siRNA/miRNA into an RNA Induced Silencing Complex (RISC), (iii) complementary base pairing between siRNA/miRNA with a targeted gene, and (iv) the cleavage or repression of a target gene with an Argonaute (AGO) protein. This natural RNAi pathway could introduce transgenes targeting various viral genes to induce gene silencing. Different RNAi pathways are reported for the artificial silencing of viral genes. These include Host-Induced Gene Silencing (HIGS), Virus-Induced Gene Silencing (VIGS), and Spray-Induced Gene Silencing (SIGS). There are significant limitations in HIGS and VIGS technology, such as lengthy and time-consuming processes, off-target effects, and public concerns regarding genetically modified (GM) transgenic plants. Here, we provide in-depth knowledge regarding SIGS, which efficiently provides RNAi resistance development against targeted genes without the need for GM transgenic plants. We give an overview of the defense system of plants against viral infection, including a detailed mechanism of RNAi, small RNA molecules and their types, and various kinds of RNAi pathways. This review will describe how RNA interference provides the antiviral defense, recent improvements, and their limitations.

Differential gene expression in aphids following virus acquisition from plants or from an artificial medium

BACKGROUND

Poleroviruses, such as turnip yellows virus (TuYV), are plant viruses strictly transmitted by aphids in a persistent and circulative manner. Acquisition of either virus particles or plant material altered by virus infection is expected to induce gene expression deregulation in aphids which may ultimately alter their behavior.

RESULTS

By conducting an RNA-Seq analysis on viruliferous aphids fed either on TuYV-infected plants or on an artificial medium containing purified virus particles, we identified several hundreds of genes deregulated in Myzus persicae, despite non-replication of the virus in the vector. Only a few genes linked to receptor activities and/or vesicular transport were common between the two modes of acquisition with, however, a low level of deregulation. Behavioral studies on aphids after virus acquisition showed that M. persicae locomotion behavior was affected by feeding on TuYV-infected plants, but not by feeding on the artificial medium containing the purified virus particles. Consistent with this, genes potentially involved in aphid behavior were deregulated in aphids fed on infected plants, but not on the artificial medium.

CONCLUSIONS

These data show that TuYV particles acquisition alone is associated with a moderate deregulation of a few genes, while higher gene deregulation is associated with aphid ingestion of phloem from TuYV-infected plants. Our data are also in favor of a major role of infected plant components on aphid behavior.

Light-Engineering Technology for Enhancing Plant Disease Resistance

Insect vector-borne diseases are a major constraint to a wide variety of crops. Plants integrate environmental light and internal signalings to defend dual stresses both from the vector insects and vector-transmitted pathogens. In this review, we highlight a studies that demonstrate how light regulates plants deploying mechanisms against vector-borne diseases. Four major host defensive pathways involved in the host defense network against multiple biotic stresses are reviewed: innate immunity, phytohormone signaling, RNA interference, and protein degradation. The potential with light-engineering technology with light emitting diodes (LEDs) and genome engineering technology for fine-tuning crop defense and yield are also discussed.

Crystal structure of the potato leafroll virus coat protein and implications for viral assembly

Luteoviruses, poleroviruses, and enamoviruses are insect-transmitted, agricultural pathogens that infect a wide array of plants, including staple food crops. Previous cryo-electron microscopy studies of virus-like particles show that luteovirid viral capsids are built from a structural coat protein that organizes with T = 3 icosahedral symmetry. Here, we present the crystal structure of a truncated version of the coat protein monomer from potato leafroll virus at 1.80-Å resolution. In the crystal lattice, monomers pack into flat sheets that preserve the two-fold and three-fold axes of icosahedral symmetry and show minimal structural deviations when compared to the full-length subunits of the assembled virus-like particle. These observations have important implications in viral assembly and maturation and suggest that the CP N-terminus and its interactions with RNA play an important role in generating capsid curvature.

A Simple Method for the Acquisition and Transmission of Brassica Yellows Virus from Transgenic Plants and Frozen Infected Leaves by Aphids

Brassica yellows virus (BrYV) is a tentative species of the genus Polerovirus, which occurs widely, and mostly damages Brassicaceae plants in East Asia. Because BrYV cannot be transmitted mechanically, an insect-based transmission method is required for further virus research. Here, a reliable and unrestricted method is described, in which non-viruliferous aphids (Myzus persicae) acquired BrYV from transgenic Arabidopsis thaliana, harboring the full-length viral genome germinated from seeds and its frozen leaves. The aphids then transmitted the virus to healthy plants. There was no significant difference in acquisition rates between fresh and frozen infected leaves, although the transmission rate from frozen infected leaves was lower compared to fresh infected leaves. This simple novel method may be used to preserve viral inocula, evaluate host varietal resistance to BrYV, and investigate interactions among BrYV, aphids, and hosts.

Virome in adult Aedes albopictus captured during different seasons in Guangzhou City, China

Background

The mosquito Aedes albopictus is an important vector for many pathogens. Understanding the virome in Ae. albopictus is critical for assessing the risk of disease transmission, implementation of vector control measures, and health system strengthening.

Methods

In this study, viral metagenomic and PCR methods were used to reveal the virome in adult Ae. albopictus captured in different areas and during different seasons in Guangzhou, China.

Results

The viral composition of adult Ae. albopictus varied mainly between seasons. Over 50 viral families were found, which were specific to vertebrates, invertebrates, plants, fungi, bacteria, and protozoa. In rural areas, Siphoviridae (6.5%) was the most common viral family harbored by mosquitoes captured during winter and spring, while Luteoviridae (1.1%) was the most common viral family harbored by mosquitoes captured during summer and autumn. Myoviridae (7.0% and 1.3%) was the most common viral family in mosquitoes captured in urban areas during all seasons. Hepatitis B virus (HBV) was detected by PCR in a female mosquito pool. The first near full-length HBV genome from Ae. albopictus was amplified, which showed a high level of similarity with human HBV genotype B sequences. Human parechovirus (HPeV) was detected in male and female mosquito pools, and the sequences were clustered with HPeV 1 and 3 sequences.

Conclusions

Large numbers of viral species were found in adult Ae. albopictus, including viruses from vertebrates, insects, and plants. The viral composition in Ae. albopictus mainly varied between seasons. Herein, we are the first to report the detection of HPeV and HBV in mosquitoes. This study not only provides valuable information for the control and prevention of mosquito-borne diseases, but it also demonstrates the feasibility of xenosurveillance.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04922-z.

Affinity Purification-Mass Spectrometry Identifies a Novel Interaction between a Polerovirus and a Conserved Innate Immunity Aphid Protein that Regulates Transmission Efficiency

The vast majority of plant viruses are transmitted by insect vectors, with many crucial aspects of the transmission process being mediated by key protein-protein interactions. Still, very few vector proteins interacting with viruses have been identified and functionally characterized. Potato leafroll virus (PLRV) is transmitted most efficiently by Myzus persicae, the green peach aphid, in a circulative, non-propagative manner. Using affinity purification coupled to high-resolution mass spectrometry (AP-MS), we identified 11 proteins from M. persicaedisplaying a high probability of interaction with PLRV and an additional 23 vector proteins with medium confidence interaction scores. Three of these aphid proteins were confirmed to directly interact with the structural proteins of PLRV and other luteovirid species via yeast two-hybrid. Immunolocalization of one of these direct PLRV-interacting proteins, an orthologue of the human innate immunity protein complement component 1 Q subcomponent-binding protein (C1QBP), shows that MpC1QBP partially co-localizes with PLRV in cytoplasmic puncta and along the periphery of aphid gut epithelial cells. Artificial diet delivery to aphids of a chemical inhibitor of C1QBP leads to increased PLRV acquisition by aphids and subsequently increased titer in inoculated plants, supporting a role for C1QBP in the acquisition and transmission efficiency of PLRV by M. persicae. This study presents the first use of AP-MS for the in vivo isolation of a functionally relevant insect vector-virus protein complex. MS data are available from ProteomeXchange.org using the project identifier PXD022167.

Genetic Variability and Molecular Evolution of Maize Yellow Mosaic Virus Populations from Different Geographic Origins

Maize yellow mosaic virus (MaYMV) hosted in various gramineous plants was assigned to the genus Polerovirus (family Luteoviridae) in 2018. However, little is known about its genetic diversity and population structure. In this study, 509 sugarcane leaf samples with mosaic symptoms were collected in 2017 to 2019 from eight sugarcane-growing provinces in China. Reverse-transcription PCR results revealed that four positive-sense RNA viruses were found to infect sugarcane, and the incidence of MaYMV among samples from Fujian, Sichuan, and Guangxi Provinces was 52.1, 9.8, and 2.5%, respectively. Based on 82 partial MaYMV sequences and 46 whole-genome sequences from different host plants, phylogenetic analysis revealed that MaYMV populations are very closely associated with their source geographical regions (China, Africa, and South America). Pairwise identity analysis showed significant variability in genome sequences among MaYMV isolates with genomic nucleotide identities of 91.1 to 99.9%. In addition to codon mutations, insertions or deletions also contributed to genetic variability in individual coding regions, especially in the readthrough protein (P3-P5 fusion protein). Low gene flow and significant genetic differentiation of MaYMV were observed among the three geographical populations, suggesting that environmental adaptation is an important evolutionary force that shapes the genetic structure of MaYMV. Genes in the MaYMV genome were subject to strong negative or purification selection during evolution, except for the movement protein (MP), which was under positive selection pressure. This finding suggests that the MP may play an important role in MaYMV evolution. Taken together, our findings provide basic information for the development of an integrated disease management strategy against MaYMV.

RNAi technology for management of banana bunchy top disease

Banana bunchy top disease (BBTD) is one of the world's most destructive viral diseases of banana and plantain, causing up to 100% yield loss in severe cases. The disease is vectored by banana aphids (Pentalonia nigronervosa) and carried long distances through the movement of infected plant materials. The banana aphids harboring banana bunchy top virus (BBTV) present in banana producing regions are the sole vector and the most efficient method of transmitting the virus to the healthy plants. Controlling the spread of BBTD has been very challenging since no known banana germplasm is immune to BBTV. The disease can be managed with the use of virus-free planting material and roguing. However, once BBTD is established in the field, it is very difficult to eradicate or manage it. Therefore, a more sustainable way of controlling the disease is developing host plant resistance against the virus and the vector. Biotechnological strategies via RNA interference (RNAi) could be used to target the banana aphid as well as BBTV to reduce virus-associated yield losses of banana and plantain, which feed over 500 million people around the world. This review discusses the status of BBTD and perspectives on effective RNAi technologies for controlling BBTV and the vector, banana aphid, transmitting the virus as sustainable management of the disease.

Bacterial Vector-Borne Plant Diseases: Unanswered Questions and Future Directions

Vector-borne plant diseases have significant ecological and economic impacts, affecting farm profitability and forest composition throughout the world. Bacterial vector-borne pathogens have evolved sophisticated strategies to interact with their hemipteran insect vectors and plant hosts. These pathogens reside in plant vascular tissue, and their study represents an excellent opportunity to uncover novel biological mechanisms regulating intracellular pathogenesis and to contribute to the control of some of the world's most invasive emerging diseases. In this perspective, we highlight recent advances and major unanswered questions in the realm of bacterial vector-borne disease, focusing on liberibacters, phytoplasmas, spiroplasmas, and Xylella fastidiosa.

Manipulation of Jasmonate Signaling by Plant Viruses and Their Insect Vectors

Plant viruses pose serious threats to stable crop yield. The majority of them are transmitted by insects, which cause secondary damage to the plant host from the herbivore-vector's infestation. What is worse, a successful plant virus evolves multiple strategies to manipulate host defenses to promote the population of the insect vector and thereby furthers the disease pandemic. Jasmonate (JA) and its derivatives (JAs) are lipid-based phytohormones with similar structures to animal prostaglandins, conferring plant defenses against various biotic and abiotic challenges, especially pathogens and herbivores. For survival, plant viruses and herbivores have evolved strategies to convergently target JA signaling. Here, we review the roles of JA signaling in the tripartite interactions among plant, virus, and insect vectors, with a focus on the molecular and biochemical mechanisms that drive vector-borne plant viral diseases. This knowledge is essential for the further design and development of effective strategies to protect viral damages, thereby increasing crop yield and food security.

Lessons from One Fastidious Bacterium to Another: What Can We Learn about Liberibacter Species from Xylella fastidiosa

Huanglongbing is causing economic devastation to the citrus industry in Florida, and threatens the industry everywhere the bacterial pathogens in the Candidatus Liberibacter genus and their insect vectors are found. Bacteria in the genus cannot be cultured and no durable strategy is available for growers to control plant infection or pathogen transmission. However, scientists and grape growers were once in a comparable situation after the emergence of Pierce’s disease, which is caused by Xylella fastidiosa and spread by its hemipteran insect vector. Proactive quarantine and vector control measures coupled with interdisciplinary data-driven science established control of this devastating disease and pushed the frontiers of knowledge in the plant pathology and vector biology fields. Our review highlights the successful strategies used to understand and control X. fastidiosa and their potential applicability to the liberibacters associated with citrus greening, with a focus on the interactions between bacterial pathogen and insect vector. By placing the study of Candidatus Liberibacter spp. within the current and historical context of another fastidious emergent plant pathogen, future basic and applied research to develop control strategies can be prioritized.

Color morphology of Diaphorina citri influences interactions with its bacterial endosymbionts and 'Candidatus Liberibacter asiaticus'

Diaphorina citri is a vector of 'Candidatus Liberibacter asiaticus,' (CLas), associated with Huanglongbing, (HLB, or citrus greening) disease in citrus. D. citri exhibits three different color morph variants, blue, gray and yellow. Blue morphs have a greater capacity for long-distance flight as compared to non-blue morphs, but little else is known about how color morphology influences vector characteristics. In this study, we show that the color morphology of the insect is derived from pigmented cells of the fat body. Blue morphs acquire a lower level of CLas in their bodies from infected trees as compared to their gray and yellow conspecifics, referred to in this paper collectively as non-blue morphs. Accordingly, CLas titer in citrus leaves inoculated by non-blue insects was 6-fold higher than in leaves inoculated by blue insects. Blue color morphs harbored lower titers of Wolbachia and 'Candidatus Profftella armatura,' two of the D. citri bacterial endosymbionts. Expression of hemocyanin, a copper-binding oxygen transport protein responsible for the blue coloration of hemolymph of other arthropods and mollusks, was previously correlated with blue color morphology and is highly up-regulated in insects continuously reared on CLas infected citrus trees. Based on our results, we hypothesized that a reduction of hemocyanin expression would reduce the D. citri immune response and an increase in the titer of CLas would be observed. Surprisingly, a specific 3-fold reduction of hemocyanin-1 transcript levels using RNA silencing in blue adult D. citri morphs had an approximately 2-fold reduction on the titer of CLas. These results suggest that hemocyanin signaling from the fat body may have multiple functions in the regulation of bacterial titers in D. citri, and that hemocyanin is one of multiple psyllid genes involved in regulating CLas titer.

First Complete Genome Sequence of Cucurbit Aphid-Borne Yellows Virus from Pumpkin in the United States

Cucurbit aphid-borne yellows virus (CABYV) was first described in France in 1992 and since then has been reported in various parts of the world, including the United States. Here, we present the first complete genome sequence of a CABYV isolate (BL4) that was collected from pumpkin during the 2017 growing season in Oklahoma.

Cucurbit aphid-borne yellows virus (CABYV) was first described in France in 1992 and since then has been reported in various parts of the world, including the United States. Here, we present the first complete genome sequence of a CABYV isolate (BL4) that was collected from pumpkin during the 2017 growing season in Oklahoma.