Comparative proteomic analysis provides new insight into differential transmission of two begomoviruses by a whitefly

Candidatus Liberibacter asiaticus influences the emergence of the Asian citrus psyllid Diaphorina citri by regulating key cuticular proteins

The Asian citrus psyllid, Diaphorina citri, is the primary vector of the HLB pathogen, Candidatus Liberibacter asiaticus (CLas). The acquisition of CLas shortens the developmental period of nymphs, accelerating the emergence into adulthood and thereby facilitating the spread of CLas. Cuticular proteins (CPs) are involved in insect emergence. In this study, we investigated the molecular mechanisms underlying CLas-promoted emergence in D. citri via CP mediation. Here, a total of 159 CP genes were first identified in the D. citri genome. Chromosomal location analysis revealed an uneven distribution of these CP genes across the 13 D. citri chromosomes. Proteomic analysis identified 54 differentially expressed CPs during D. citri emergence, with 14 CPs exhibiting significant differential expression after CLas acquisition. Five key genes, Dc18aa-1, Dc18aa-2, DcCPR-24, DcCPR-38 and DcCPR-58, were screened from the proteome and CLas acquisition. The silencing of these 5 genes through a modified feeding method significantly reduced the emergence rate and caused various abnormal phenotypes, indicating the crucial role that these genes play in D. citri emergence. This study provides a comprehensive overview of the role of CPs in D. citri and reveals that CLas can influence the emergence process of D. citri by regulating the expression of CPs. These key CPs may serve as potential targets for future research on controlling huanglongbing (HLB) transmission.

Tomato yellow leaf curl virus: Characteristics, influence, and regulation mechanism

Tomato yellow leaf curl virus (TYLCV), a DNA virus belonging to the genus Begomovirus, significantly impedes the growth and development of numerous host plants, including tomatoes and peppers. Due to its rapid mutation rate and frequent recombination events, achieving complete control of TYLCV proves exceptionally challenging. Consequently, identifying resistance mechanisms become crucial for safeguarding host plants from TYLCV-induced damage. This review article delves into the global distribution, dispersal patterns, and defining characteristics of TYLCV. Moreover, the intricate interplay between TYLCV and various influencing factors, such as insect vectors, susceptible host plants, and abiotic stresses, plays a pivotal role in plant-TYLCV interactions. The review offers an updated perspective on recent investigations focused on plant response mechanisms to TYLCV infection, including the intricate relationship between TYLCV, whiteflies, and regulatory factors. This comprehensive analysis aims to establish a foundation for future research endeavors exploring the molecular mechanisms underlying TYLCV infection and the development of plant resistance through breeding programs.

Transcriptomic and Proteomic Analyses of Myzus persicae Carrying Brassica Yellows Virus

Viruses in the genus Polerovirus infect a wide range of crop plants and cause severe economic crop losses. BrYV belongs to the genus Polerovirus and is transmitted by Myzus persicae. However, the changes in transcriptome and proteome profiles of M. persicae during viral infection are unclear. Here, RNA-Seq and TMT-based quantitative proteomic analysis were performed to compare the differences between viruliferous and nonviruliferous aphids. In total, 1266 DEGs were identified at the level of transcription with 980 DEGs being upregulated and 286 downregulated in viruliferous aphids. At the protein level, among the 18 DEPs identified, the number of upregulated proteins in viruliferous aphids was twice that of the downregulated DEPs. Enrichment analysis indicated that these DEGs and DEPs were mainly involved in epidermal protein synthesis, phosphorylation, and various metabolic processes. Interestingly, the expressions of a number of cuticle proteins and tubulins were upregulated in viruliferous aphids. Taken together, our study revealed the complex regulatory network between BrYV and its vector M. persicae from the perspective of omics. These findings should be of great benefit to screening key factors involved in the process of virus circulation in aphids and provide new insights for BrYV prevention via vector control in the field.

Cassava begomovirus species diversity changes during plant vegetative cycles

Cassava is a root crop important for global food security and the third biggest source of calories on the African continent. Cassava production is threatened by Cassava mosaic disease (CMD), which is caused by a complex of single-stranded DNA viruses (family: Geminiviridae, genus: Begomovirus) that are transmitted by the sweet potato whitefly (Bemisia tabaci). Understanding the dynamics of different cassava mosaic begomovirus (CMB) species through time is important for contextualizing disease trends. Cassava plants with CMD symptoms were sampled in Lake Victoria and coastal regions of Kenya before transfer to a greenhouse setting and regular propagation. The field-collected and greenhouse samples were sequenced using Illumina short-read sequencing and analyzed on the Galaxy platform. In the field-collected samples, African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), East African cassava mosaic Kenya virus (EACMKV), and East African cassava mosaic virus-Uganda variant (EACMV-Ug) were detected in samples from the Lake Victoria region, while EACMV and East African mosaic Zanzibar virus (EACMZV) were found in the coastal region. Many of the field-collected samples had mixed infections of EACMV and another begomovirus. After 3 years of regrowth in the greenhouse, only EACMV-like viruses were detected in all samples. The results suggest that in these samples, EACMV becomes the dominant virus through vegetative propagation in a greenhouse. This differed from whitefly transmission results. Cassava plants were inoculated with ACMV and another EACMV-like virus, East African cassava mosaic Cameroon virus (EACMCV). Only ACMV was transmitted by whiteflies from these plants to recipient plants, as indicated by sequencing reads and copy number data. These results suggest that whitefly transmission and vegetative transmission lead to different outcomes for ACMV and EACMV-like viruses.

Combined Transcriptomic and Proteomic Analysis of Myzus persicae, the Green Peach Aphid, Infected with Cucumber Mosaic Virus

Simple Summary

In this study, an integrated analysis of the mRNA and protein was performed to identify important putative regulators involved in the transmission of CMV (cucumber mosaic virus) by aphids. At the level of transcription, a total of 20,550 genes (≥2-fold expression difference) were identified as being differentially expressed genes (DEGs) 24 h after healthy aphid transfer to infected tobacco plants using the RNA-seq approach. At the protein level, 744 proteins were classified as being differentially abundant between virus-treated and control Myzus persicae using iTRAQ (isobaric tags for relative and absolute quantitation) analysis. The combined mRNA and protein analysis enabled the identification of some viral putative regulators, such as cuticle proteins, ribosomal proteins, and cytochrome P450 enzymes. The results show that most of the key putative regulators were highly accumulated at the protein level. Based on those findings, we can speculate that the process by which aphids spread CMV is mainly related to post-translational regulation rather than transcription.

Abstract

Aphids transmit CMV (cucumber mosaic virus) in a non-persistent manner. However, little is known about the mechanism of CMV transmission. In this study, an integrated analysis of the mRNA and protein was performed to identify important putative regulators involved in the transmission of CMV by aphids. At the level of transcription, a total of 20,550 genes (≥2-fold expression difference) were identified as being differentially expressed genes (DEGs) 24 h after healthy aphid transfer to infected tobacco plants using the RNA-seq approach. At the protein level, 744 proteins were classified as being differentially abundant between virus-treated and control M. persicae using iTRAQ (isobaric tags for relative and absolute quantitation) analysis. The combined mRNA and protein analysis enabled the identification of some viral putative regulators, such as cuticle proteins, ribosomal proteins, and cytochrome P450 enzymes. The results show that most of the key putative regulators were highly accumulated at the protein level. Based on those findings, we can speculate that the process by which aphids spread CMV is mainly related to post-translational regulation rather than transcription.

Insect Transmission of Plant Single-Stranded DNA Viruses

Of the approximately 1,200 plant virus species that have been described to date, nearly one-third are single-stranded DNA (ssDNA) viruses, and all are transmitted by insect vectors. However, most studies of vector transmission of plant viruses have focused on RNA viruses. All known plant ssDNA viruses belong to two economically important families, Geminiviridae and Nanoviridae, and in recent years, there have been increased efforts to understand whether they have evolved similar relationships with their respective insect vectors. This review describes the current understanding of ssDNA virus-vector interactions, including how these viruses cross insect vector cellular barriers, the responses of vectors to virus circulation, the possible existence of viral replication within insect vectors, and the three-way virus-vector-plant interactions. Despite recent breakthroughs in our understanding of these viruses, many aspects of plant ssDNA virus transmission remain elusive. More effort is needed to identify insect proteins that mediate the transmission of plant ssDNA viruses and to understand the complex virus-insect-plant three-way interactions in the field during natural infection.

A vector whitefly endocytic receptor facilitates the entry of begomoviruses into its midgut cells via binding to virion capsid proteins

Many circulative plant viruses transmitted by insect vectors are devastating to agriculture worldwide. The midgut wall of vector insects represents a major barrier and at the same time the key gate a circulative plant virus must cross for productive transmission. However, how these viruses enter insect midgut cells remains poorly understood. Here, we identified an endocytic receptor complex for begomoviruses in the midgut cells of their whitefly vector. Our results show that two whitefly proteins, BtCUBN and BtAMN, compose a receptor complex BtCubam, for which BtCUBN contributes a viral-binding region and BtAMN contributes to membrane anchorage. Begomoviruses appear to be internalized together with BtCubam via its interaction with the 12–19 CUB domains of BtCUBN via clathrin-dependent endocytosis. Functional analysis indicates that interruption of BtCUBN and BtAMN lead to reduction of virus acquisition and transmission by whitefly. In contrast, CUBN-begomovirus interaction was not observed in two non-competent whitefly-begomovirus combinations. These observations suggest a major role of the specific endocytic receptor in facilitating viral entry into vector midgut cells.

Many viruses depend on insect vectors for transmission and spread. Following ingestion by insect vectors, many viruses need to circulate in the vector via a sequential path of stylet-midgut-haemolymph-salivary glands and are finally inoculated into plants with saliva secretion. To complete this journey, virions have to cross many physical/physiological barriers, of which the insect midgut wall represents the first and one of the major challenges. While this route of virus circulation has been known for a long time, the physiological and molecular mechanisms underlying the crossing of these barriers by viruses are poorly understood. Working with begomoviruses, a group of plant viruses of economic significance worldwide, and their insect vectors, the whiteflies of the Bemisia tabaci complex, we found that upon virus infection, two vector proteins, cubilin (CUBN) and amnionless (AMN), form a virus receptor complex to uptake the virions and assist them to move through the apical membrane of whitefly midgut cells via clathrin-dependent endocytosis. These novel findings contribute to a better understanding on the molecular mechanisms of insect transmission of circulative viruses.

Plant-virus-insect tritrophic interactions: insights into the functions of geminivirus virion-sense strand genes

The genome of the plant-infecting viruses in the family Geminiviridae is composed of one or two circular single stranded DNA of approximately 2.7-5.2 kb in length. These viruses have emerged as the most devastating pathogen infecting a large number of crops and weeds across the continents. They code for fewer open reading frames (ORFs) through the generation of overlapping transcripts derived from the bidirectional viral promoters. Members of geminiviruses code for up to four ORFs in the virion-sense strand, and their gene expression is regulated by various cis-elements located at their promoters in the intergenic region. These viral proteins perform multiple functions at every stage of the viral life cycle such as virus transport, insect-mediated virus transmission and suppression of host defence. They impede the host's multi-layered antiviral mechanisms including gene silencing (at transcriptional and post-transcriptional levels) and hypersensitive response. This review summarizes the essential role of virion-sense strand encoded proteins in transport of viral genomes within and between plant cells, countering defence in hosts (both plants and the insects), and also in the ubiquitous role in vector-mediated transmission. We highlight the significance of their pro-viral activities in manipulating host-derived innate immune responses and the interaction with whitefly-derived proteins. We also discuss the current knowledge on virus replication and transcription within the insect body.

Characterization of Local and Systemic Impact of Whitefly (Bemisia tabaci) Feeding and Whitefly-Transmitted Tomato Mottle Virus Infection on Tomato Leaves by Comprehensive Proteomics

Tomato mottle virus (ToMoV) is a single-stranded DNA (ssDNA) begomovirus transmitted to solanaceous crops by the whitefly species complex (Bemisia tabaci), causing stunted growth, leaf mottling, and reduced yield. Using a genetic repertoire of seven genes, ToMoV pathogenesis includes the manipulation of multiple plant biological processes to circumvent antiviral defenses. To further understand the effects of whitefly feeding and whitefly-transmitted ToMoV infection on tomato plants (Solanum lycopersicum ‘Florida Lanai’), we generated comprehensive protein profiles of leaves subjected to feeding by either viruliferous whiteflies harboring ToMoV, or non-viruliferous whiteflies, or a no-feeding control. The effects of whitefly feeding and ToMoV infection were measured both locally and systemically by sampling either a mature leaf directly from the site of clip-cage confined whitefly feeding, or from a newly formed leaf 10 days post feeding (dpf). At 3 dpf, tomato’s response to ToMoV included proteins associated with translation initiation and elongation as well as plasmodesmata dynamics. In contrast, systemic impacts of ToMoV on younger leaves 10 dpf were more pronounced and included a virus-specific change in plant proteins associated with mRNA maturation and export, RNA-dependent DNA methylation, and other antiviral plant processes. Our analysis supports previous findings and provides novel insight into tomato’s local and systemic response to whitefly feeding and ToMoV infection.

Applications of Proteomic Tools to Study Insect Vector-Plant Virus Interactions

Proteins are crucial players of biological interactions within and between the organisms and thus it is important to understand the role of proteins in successful partnerships, such as insect vectors and their plant viruses. Proteomic approaches have identified several proteins at the interface of virus acquisition and transmission by their insect vectors which could be potential molecular targets for sustainable pest and viral disease management strategies. Here we review the proteomic techniques used to study the interactions of insect vector and plant virus. Our review will focus on the techniques available to identify the infection, global changes at the proteome level in insect vectors, and protein-protein interactions of insect vectors and plant viruses. Furthermore, we also review the integration of other techniques with proteomics and the available bioinformatic tools to analyze the proteomic data.

Transcriptome Analysis of Gene Expression Profiles of Tomato Yellow Leaf Curl Virus-Infected Whiteflies over Different Viral Acquisition Access Periods

Tomato yellow leaf curl virus (TYLCV), which is transmitted by Bemisia tabaci in a persistent-circulative manner, threatens tomato production worldwide. Little is known about the complicated interaction during this process at the molecular level. In this study, viral AAPs at 0 h, 2 h, 6 h, 12 h and 48 h were investigated using a comparative transcriptome analysis to uncover the transcriptional responses of whiteflies to virus infection. Our results have shown that 755, 587, 1140 and 1347 differentially expressed genes (DEGs) were identified in the comparisons of the data of 0 h vs. 2 h, 0 h vs. 6 h, 0 h vs. 12 h and 0 h vs. 48 h, respectively. KEGG analysis showed that DEGs associated with metabolisms and signal transduction were down-regulated in virus-infected whiteflies. Additionally, 16 up-regulated putative transporter genes and 10 down-regulated genes associated with IL-17 signaling pathway were identified by time-associated gene cluster analysis. These data boost our comprehensions on whitefly-TYLCV interactions associated with different viral AAPs.

Molecular insight into cotton leaf curl geminivirus disease resistance in cultivated cotton (Gossypium hirsutum)

Cultivated cotton (Gossypium hirsutum) is the most important fibre crop in the world. Cotton leaf curl disease (CLCuD) is the major limiting factor and a threat to textile industry in India and Pakistan. All the local cotton cultivars exhibit moderate to no resistance against CLCuD. In this study, we evaluated an exotic cotton accession Mac7 as a resistance source to CLCuD by challenging it with viruliferous whiteflies and performing qPCR to evaluate the presence/absence and relative titre of CLCuD-associated geminiviruses/betasatellites. The results indicated that replication of pathogenicity determinant betasatellite is significantly attenuated in Mac7 and probably responsible for resistance phenotype. Afterwards, to decipher the genetic basis of CLCuD resistance in Mac7, we performed RNA sequencing on CLCuD-infested Mac7 and validated RNA-Seq data with qPCR on 24 independent genes. We performed co-expression network and pathway analysis for regulation of geminivirus/betasatellite-interacting genes. We identified nine novel modules with 52 hubs of highly connected genes in network topology within the co-expression network. Analysis of these hubs indicated the differential regulation of auxin stimulus and cellular localization pathways in response to CLCuD. We also analysed the differential regulation of geminivirus/betasatellite-interacting genes in Mac7. We further performed the functional validation of selected candidate genes via virus-induced gene silencing (VIGS). Finally, we evaluated the genomic context of resistance responsive genes and found that these genes are not specific to A or D sub-genomes of G. hirsutum. These results have important implications in understanding CLCuD resistance mechanism and developing a durable resistance in cultivated cotton.

Gene Expression in the Salivary Gland of Rhipicephalus (Boophilus) microplus Fed on Tick-Susceptible and Tick-Resistant Hosts

The success of cattle tick fixation largely depends on the secretion of substances that alter the immune response of the host. The majority of these substances are expressed by the parasite salivary gland and secreted in tick saliva. It is known that hosts can mount immune responses against ticks and bovine European breeds, and bovine industrial crossbreeds are more susceptible to infestations than are Bos indicus cattle. To identify candidates for the development of novel control strategies for the cattle tick Rhipicephalus (Boophilus) microplus, a salivary gland transcriptome analysis of engorged females fed on susceptible or resistant hosts was performed. Using RNA-Seq, transcriptomes were de novo assembled and produced a total of 235,451 contigs with 93.3% transcriptome completeness. Differential expression analysis identified 137 sequences as differentially expressed genes (DEGs) between ticks raised on tick-susceptible or tick-resistant cattle. DEGs predicted to be secreted proteins include innexins, which are transmembrane proteins that form gap junction channels; the transporters Na⁺/dicarboxylate, Na⁺/tricarboxylate, and phosphate transporter and a putative monocarboxylate transporter; a phosphoinositol 4-phosphate adaptor protein; a cysteine-rich protein containing a trypsin inhibitor-like (TIL) domain; a putative defense protein 3 containing a reeler domain; and an F-actin-uncapping protein LRRC16A with a CARMIL_C domain; these genes were upregulated in ticks fed on tick-susceptible cattle. DEGs predicted to be non-secreted proteins included a small heat shock protein and the negative elongation factor B-like, both acting in a coordinated manner to increase HSP transcript levels in the salivary glands of the ticks fed on tick-susceptible cattle; the 26S protease regulatory subunit 6B and another chaperone with similarity to calnexin, also upregulated in ticks fed on tick-susceptible cattle; an EF-hand calcium binding protein and a serine carboxypeptidase (SCP), both involved in the blood coagulation cascade and upregulated in ticks fed on tick-susceptible cattle; and two ribosomal proteins, the 60S acidic ribosomal protein P2 and the 60S ribosomal protein L19. These results help to characterize cattle tick salivary gland gene expression in tick-susceptible and tick-resistant hosts and suggest new putative targets for the control of tick infestations, as those genes involved in the mechanism of stress response during blood feeding.

Plant Antiviral Immunity Against Geminiviruses and Viral Counter-Defense for Survival

The family Geminiviridae includes plant-infecting viruses whose genomes are composed of one or two circular non-enveloped ssDNAs(+) of about 2.5-5.2 kb each in size. These insect-transmissible geminiviruses cause significant crop losses across continents and pose a serious threat to food security. Under the control of promoters generally located within the intergenic region, their genomes encode five to eight ORFs from overlapping viral transcripts. Most proteins encoded by geminiviruses perform multiple functions, such as suppressing defense responses, hijacking ubiquitin-proteasomal pathways, altering hormonal responses, manipulating cell cycle regulation, and exploiting protein-signaling cascades. Geminiviruses establish complex but coordinated interactions with several host elements to spread and facilitate successful infection cycles. Consequently, plants have evolved several multilayered defense strategies against geminivirus infection and distribution. Recent studies on the evasion of host-mediated resistance factors by various geminivirus proteins through novel mechanisms have provided new insights into the development of antiviral strategies against geminiviruses. This review summarizes the current knowledge concerning virus movement within and between cells, as well as the recent advances in our understanding of the biological roles of virus-encoded proteins in manipulating host-mediated responses and insect transmission. This review also highlights unexplored areas that may increase our understanding of the biology of geminiviruses and how to combat these important plant pathogens.

Transovarial transmission of tomato yellow leaf curl virus by seven species of the Bemisia tabaci complex indigenous to China: Not all whiteflies are the same

Begomoviruses contain some of the most damaging viral disease agents of crops worldwide, and are transmitted by whiteflies of the Bemisia tabaci species complex. During the last 20 years, transovarial transmission of tomato yellow leaf curl virus (TYLCV) has been reported in two invasive species of the B. tabaci complex. To further decipher the importance of this mode of transmission, we analyzed transovarial transmission of TYLCV by seven whitefly species indigenous to China. TYLCV virions were detected in eggs of all species except one, and in nymphs of two species, but in none of the ensuing adults of all seven species. Our results suggest that these indigenous whiteflies are unable to transmit TYLCV, a begomovirus alien to China, via ova to produce future generations of viruliferous adults, although most of the species exhibit varying ability to carry over the virus to the eggs/nymphs of their offspring via transovarial transmission.