Biological invasions of geminiviruses: case study of TYLCV and Bemisia tabaci in Reunion Island

A Review of Interactions between Plants and Whitefly-Transmitted Begomoviruses

The transmission of plant viruses from infected to healthy host plants is a process in which insects play a major role, using various transmission strategies. Environmental factors have an impact on the transmission of viruses and the subsequent development of infections or diseases. When viruses are successful, plant virus diseases can reach epidemic proportions. Many plants across different regions are vulnerable to viral infections transmitted by the whitefly vector. Begomoviruses, which are transmitted by whiteflies, represent a significant threat to agriculture worldwide. The review highlights the mechanisms of virus acquisition and transmission by whiteflies and explores the factors influencing these interactions. Understanding the impacts of these changes is crucial for managing the spread of pests and mitigating damage to crops. It underscores the need for continued research to elucidate the mechanisms driving plant-insect-virus interactions and to identify new approaches for sustainable pest management.

Crinivirus Tomato Chlorosis Virus Compromises the Control of Tomato Yellow Leaf Curl Virus in Tomato Plants by the Ty-1 Gene

Tomato yellow leaf curl disease (TYLCD) causes severe damage to tomato crops in warm regions of the world, and is associated with infections of several whitefly (Bemisia tabaci)-transmitted single-stranded (ss)DNA begomoviruses (genus Begomovirus, family Geminiviridae). The most widespread begomovirus isolates associated with TYLCD are those of the type strain of the Tomato yellow leaf curl virus species, known as Israel (TYLCV-IL). The Ty-1 gene is widely used in commercial tomato cultivars to control TYLCV-IL damage, providing resistance to the virus by restricting viral accumulation and tolerance to TYLCD by inhibiting disease symptoms. However, several reports suggest that TYLCV-IL-like isolates are adapting to the Ty-1 gene and are causes of concern for possibly overcoming the provided control. This is the case with TYLCV-IL IS76-like recombinants that have a small genome fragment acquired by genetic exchange from an isolate of Tomato yellow leaf curl Sardinia virus, another begomovirus species associated with TYLCD. Here we show that TYLCV-IL IS76-like isolates partially break down the TYLCD-tolerance provided by the Ty-1 gene and that virulence differences might exist between isolates. Interestingly, we demonstrate that mixed infections with an isolate of the crinivirus (genus Crinivirus, family Closteroviridae) species Tomato chlorosis virus (ToCV), an ssRNA virus also transmitted by B. tabaci and emerging worldwide in tomato crops, boosts the breakdown of the TYLCD-tolerance provided by the Ty-1 gene either with TYLCV-IL IS76-like or canonical TYLCV-IL isolates. Moreover, we demonstrate the incorporation of the Ty-2 gene in Ty-1-commercial tomatoes to restrict (no virus or virus traces, no symptoms) systemic infections of recombinant TYLCV-IL IS76-like and canonical TYLCV-IL isolates, even in the presence of ToCV infections, which provides more robust and durable control of TYLCD.

Limited role of recombination in the global diversification of begomovirus DNA-B proteins

Approximately half of the characterized begomoviruses have bipartite genomes, but the second genomic segment, the DNA-B, is understudied relative to the DNA-A, which is homologous to the entire genome of monopartite begomoviruses. We examined the evolutionary history of the two proteins encoded by the DNA-B, the genes of which make up ∼60% of the DNA-B segment, from all bipartite begomovirus species. Our dataset of 131 movement protein (MP) and nuclear shuttle protein (NSP) sequences confirmed the deep split between Old World (OW) and New World (NW) species, and showed strong support for deep, congruent branches among the OW sequences of the MP and NSP. NW sequences were much less diverse and had poor phylogenetic resolution; over half of nodes in both the NSP and MP NW clades were supported by <50% bootstrap support. This poor resolution hampered our ability to detect incongruent phylogenies between the MP and NSP datasets, and we found no statistical evidence for recombination within our MP and NSP datasets. Finally, we quantified the sequence diversity between the NW and OW proteins, showing that the NW MP has particularly low diversity, suggesting it has been subject to different evolutionary pressures than the NW NSP.

An Overview of Chili Leaf Curl Disease: Molecular Mechanisms, Impact, Challenges, and Disease Management Strategies in Indian Subcontinent

Leaf curl disease in a chili plant is caused mainly by Chili leaf curl virus (ChiLCV) (Family: Geminiviridae, Genus: Begomovirus). ChiLCV shows a widespread occurrence in most of the chili (Capsicum spp.) growing regions. ChiLCV has a limited host range and infects tomatoes (Solanum lycopersicum), potatoes (S. tuberosum), and amaranth (Amaranthus tricolor). The virus genome is a monopartite circular single-stranded DNA molecule of 2.7 kb and associated with α and β-satellites of 1.3 and 1.4 kb, respectively. The virus genome is encapsulated in distinct twinned icosahedral particles of around 18-30 nm in size and transmitted by Bemisia tabaci (Family: Aleyrodidae, Order: Hemiptera). Recently, bipartite begomovirus has been found to be associated with leaf curl disease. The leaf curl disease has a widespread distribution in the major equatorial regions viz., Australia, Asia, Africa, Europe, and America. Besides the PCR, qPCR, and LAMP-based detection systems, recently, localized surface-plasmon-resonance (LPSR) based optical platform is used for ChiLCV detection in a 20-40 μl of sample volume using aluminum nanoparticles. Management of ChiLCV is more challenging due to the vector-borne nature of the virus, therefore integrated disease management strategies need to be followed to contain the spread and heavy crop loss. CRISPR/Cas-mediated virus resistance has gained importance in disease management of DNA and RNA viruses due to certain advantages over the conventional approaches. Therefore, CRISPR/Cas system-mediated resistance needs to be explored in chili against ChiLCV.

The Establishment and Spread of a Newly Introduced Begomovirus in a Dry Tropical Environment Using Tomato Yellow Leaf Curl Virus as a Case Study

Early detection of tomato yellow leaf curl virus (TYLCV) in a previously unaffected tomato production district in Australia allowed its spread to be evaluated spatially and temporally. The population dynamics of the TYLCV vector, Bemisia argentifolii (silverleaf whitefly, SLW), were also evaluated. The district is a dry tropical environment with a clear break to commercial production during the summer wet season. The incidence of TYLCV within crops and its prevalence through the district was influenced by weather, location, vector movements, and the use of Ty-1 virus-resistant hybrids. Rainfall had an important influence, with late summer and early autumn rain suppressing the levels of SLW and, by contrast, a dry summer supporting faster population growth. The use of Ty-1 hybrids appears to have reduced the incidence of TYLCV in this district. There was limited use of Ty-1 hybrids during 2013, and by season end, crops had moderate levels of SLW and high virus incidence. The 2015 and early 2016 season had high SLW populations, but TYLCV incidence was lower than in 2013, possibly due to the widespread adoption of the Ty-1 hybrids reducing virus spread. This study provides valuable epidemiology data for future incursions of begomoviruses, and other viruses spread by SLW.

Gut-Expressed Vitellogenin Facilitates the Movement of a Plant Virus across the Midgut Wall in Its Insect Vector

Many viral pathogens of global importance to plant and animal health are persistently transmitted by insect vectors. Midgut of insects forms the first major barrier that these viruses encounter during their entry into the vectors. However, the vector ligand(s) involved in the movement of plant viruses across the midgut barrier remains largely uncharacterized. Begomoviruses, many of which are disease agents of some major crops worldwide, are persistently transmitted by whiteflies (Bemisia tabaci). Here, in order to identify whitefly midgut proteins that interact with a devastating begomovirus, tomato yellow leaf curl virus (TYLCV), we performed midgut-specific TYLCV coat protein (CP) immunoprecipitation followed by high-throughput mass spectrometry proteomic analysis. We find that vitellogenin (Vg), a critical insect reproductive protein that has been considered to be synthesized by the fat body, is also synthesized by and interacts with TYLCV CP in the whitefly midgut. TYLCV appears to be internalized into midgut epithelial cells as a complex with Vg through endocytosis. Virus-containing vesicles then deliver the virus-Vg complexes to early endosomes for intracellular transport. Systematic silencing of Vg or midgut-specific immune blocking of Vg inhibited virus movement across the midgut wall and decreased viral acquisition and transmission by whitefly. Our findings show that a functional Vg protein is synthesized in the midgut of an insect and suggest a novel Vg mechanism that facilitates virus movement across the midgut barrier of its insect vector.

IMPORTANCE An essential step in the life cycle of many viruses is transmission to a new host by insect vectors, and one critical step in the transmission of persistently transmitted viruses is overcoming the midgut barrier to enter vectors and complete their cycle. Most viruses enter vector midgut epithelial cells via specific interaction between viral structural proteins and vector cell surface receptor complexes. Tomato yellow leaf curl virus (TYLCV) is persistently transmitted by the whitefly Bemisia tabaci between host plants. Here, we find that TYLCV coat protein interacts with vitellogenin (Vg) in the whitefly midgut. This interaction is required for the movement of the virus crossing the midgut wall and thus facilitates viral acquisition and transmission by whitefly. This study reveals a novel mechanism of virus overcoming the insect midgut barrier and provides new insights into the function of Vg beyond serving as nutrition for developing embryos in insects.

Homo sapiens: The Superspreader of Plant Viral Diseases

Plant viruses are commonly vectored by flying or crawling animals, such as aphids and beetles, and cause serious losses in major agricultural and horticultural crops. Controlling virus spread is often achieved by minimizing a crop's exposure to the vector, or by reducing vector numbers with compounds such as insecticides. A major, but less obvious, factor not controlled by these measures is Homo sapiens. Here, we discuss the inconvenient truth of how humans have become superspreaders of plant viruses on both a local and a global scale.

Tomato Yellow Leaf Curl Virus: Impact, Challenges, and Management

Tomato yellow leaf curl virus (TYLCV) is one of the most studied plant viral pathogens because it is the most damaging virus for global tomato production. In order to combat this global threat, it is important that we understand the biology of TYLCV and devise management approaches. The prime objective of this review is to highlight management strategies for efficiently tackling TYLCV epidemics and global spread. For that purpose, we focus on the impact TYLCV has on worldwide agriculture and the role of recent advances for our understanding of TYLCV interaction with its host and vector. Another important focus is the role of recombination and mutations in shaping the evolution of TYLCV genome and geographical distribution.

Begomovirus-Associated Betasatellite Virulence Factor βC1 Attenuates Tobacco Defense to Whiteflies via Interacting With Plant SKP1

Plant-mediated interactions between plant viruses and their vectors are important determinants of the population dynamics of both types of organisms in the field. The whitefly Bemisia tabaci can establish mutualism with begomoviruses via their shared host plants. This mutualism is achieved by the interaction between virulence factors and their host proteins. While the virulence factor βC1 encoded by tomato yellow leaf curl China betasatellite (TYLCCNB), a subviral agent associated to the begomovirus tomato yellow leaf curl China virus (TYLCCNV), may interact with plant protein MYC2, thereby establishing the indirect mutualism between TYLCCNV and whitefly, whether other mechanisms are involved remains unknown. Here, we found the in vitro and in vivo interactions between βC1 and tobacco protein S-phase kinase associated protein 1 (NtSKP1). Silencing the expression of NtSKP1 enhanced the survival rate and fecundity of whiteflies on tobacco plants. NtSKP1 could activate the transcription of genes in jasmonic acid (JA) pathways by impairing the stabilization of JAZ1 protein. Moreover, βC1-NtSKP1 interaction could interfere JAZ1 degradation and attenuate the plant JA defense responses. These results revealed a novel mechanism underlying the better performance of whiteflies on TYLCCNV/TYLCCNB-infected plants.

C4, the Pathogenic Determinant of Tomato Leaf Curl Guangdong Virus, May Suppress Post-transcriptional Gene Silencing by Interacting With BAM1 Protein

Tomato leaf curl Guangdong virus (ToLCGdV) is a begomovirus associated with a Tomato yellow leaf curl disease (TYLCD) epidemic in Guangdong province, China. Being the least conserved protein among geminivirus proteins, the function of C4 during ToLCGdV infection has not been elucidated. In this study, the infectious clones of ToLCGdV and a ToLCGdV mutant (ToLCGdV_mC4) with disrupted C4 ORF were constructed. Although ToLCGdV and ToLCGdV_mC4 could infect Nicotiana benthamiana and tomato plants, ToLCGdV_mC4 elicited much milder symptoms compared with ToLCGdV. To further verify the role of C4 in viral pathogenesis, C4 was expressed in N. benthamiana from Potato virus X (PVX) vector. The results showed that ToLCGdV C4 enhanced the pathogenicity of PVX and induced more severe developmental abnormalities in plants compared with PVX alone or PVX-mC4. In addition, ToLCGdV C4 suppresses systemic gene silencing in the transgenic N. benthamiana line 16c, but not local gene silencing induced by sense GFP in wild-type N. benthamiana plants. Moreover, C4 suppresses transcriptional gene silencing (TGS) by reducing the DNA methylation level of 35S promoter in 16c-TGS N. benthamiana plants. Furthermore, C4 could also interact with the receptor-like kinase (RLK) BARELY ANY MERISTEM 1 (BAM1), suggesting that C4 may suppress gene silencing by interfering with the function of BAM1 in the cell-to-cell spread of RNAi. All these results suggest that C4 is a pathogenic determinant of ToLCGdV, and C4 may suppress post-transcriptional gene silencing (PTGS) by interacting with BAM1.

Revisiting Seed Transmission of the Type Strain of Tomato yellow leaf curl virus in Tomato Plants

Isolates of the Tomato yellow leaf curl virus (TYLCV) species (genus Begomovirus, family Geminiviridae) infect tomato crops worldwide, causing severe economic damage. Members of the whitefly Bemisia tabaci sibling species group are the vector of begomoviruses, including TYLCV. However, transmission of isolates of the type strain (Israel [IL]) of TYLCV (TYLCV-IL) by tomato seed has recently been reported based on infections occurring in Korea. Because of the consequences of this finding on the epidemiology and control of the disease caused by TYLCV and on the seed market, it was considered essential to revisit and expand those results to other tomato-growing areas. TYLCV DNA content was detected in tomato and Nicotiana benthamiana seed collected from plants naturally or experimentally infected with TYLCV-IL, supporting its seedborne nature. The TYLCV-IL replication detected in tomato and N. benthamiana flower reproductive organs demonstrated close association of this virus with the seed during maturation. However, the significant reduction of TYLCV DNA load after surface disinfections of tomato seed suggests that most of the virus is located externally, as contaminant of the seed coat. Transmission assays, carried out with seven tomato genotypes and more than 3,000 tomato plants, revealed no evidence of seed transmission from "surface-disinfected" or untreated seed for two Mediterranean isolates of TYLCV-IL. Similar results were also obtained for seed collected from TYLCV-IL-infected N. benthamiana plants. The results support the conclusion that TYLCV-IL is seedborne but is not seed transmitted in tomato or N. benthamiana, suggesting that transmission through seed is not a general property of TYLCV.

Tomato yellow leaf curl virus intergenic siRNAs target a host long noncoding RNA to modulate disease symptoms

Tomato yellow leaf curl virus (TYLCV) and its related begomoviruses cause fast-spreading diseases in tomato worldwide. How this virus induces diseases remains largely unclear. Here we report a noncoding RNA-mediated model to elucidate the molecular mechanisms of TYLCV-tomato interaction and disease development. The circular ssDNA genome of TYLCV contains a noncoding intergenic region (IR), which is known to mediate viral DNA replication and transcription in host cells, but has not been reported to contribute directly to viral disease development. We demonstrate that the IR is transcribed in dual orientations during plant infection and confers abnormal phenotypes in tomato independently of protein-coding regions of the viral genome. We show that the IR sequence has a 25-nt segment that is almost perfectly complementary to a long noncoding RNA (lncRNA, designated as SlLNR1) in TYLCV-susceptible tomato cultivars but not in resistant cultivars which contains a 14-nt deletion in the 25-nt region. Consequently, we show that viral small-interfering RNAs (vsRNAs) derived from the 25-nt IR sequence induces silencing of SlLNR1 in susceptible tomato plants but not resistant plants, and this SlLNR1 downregulation is associated with stunted and curled leaf phenotypes reminiscent of TYLCV symptoms. These results suggest that the lncRNA interacts with the IR-derived vsRNAs to control disease development during TYLCV infection. Consistent with its possible function in virus disease development, over-expression of SlLNR1 in tomato reduces the accumulation of TYLCV. Furthermore, gene silencing of the SlLNR1 in the tomato plants induced TYLCV-like leaf phenotypes without viral infection. Our results uncover a previously unknown interaction between vsRNAs and host lncRNA, and provide a plausible model for TYLCV-induced diseases and host antiviral immunity, which would help to develop effective strategies for the control of this important viral pathogen.

Development of a New Molecular Marker for the Resistance to Tomato Yellow Leaf Curl Virus

Tomato yellow leaf curl virus (TYLCV) responsible for tomato yellow leaf curl disease (TYLCD) causes a substantial decrease in tomato (Solanum lycopersicum L.) yield worldwide. The use of resistant variety as a sustainable management strategy has been advocated. Tremendous progress has been made in genetically characterizing the resistance genes (R gene) in tomato. Breeding tomato for TYLCV resistance has been based mostly on Ty-3 as a race-specific resistance gene by introgression originating from wild tomato species relatives. Improvement or development of a cultivar is achievable through the use of marker-assisted selection (MAS). Therefore, precise and easy use of gene-targeted markers would be of significant importance for selection in breeding programs. The present study was undertaken to develop a new marker based on Ty-3 gene sequence that can be used for MAS in TYLCV resistant tomato breeding program. The new developed marker was named ACY. The reliability and accuracy of ACY were evaluated against those of Ty-3 linked marker P6-25 through screening of commercial resistant and susceptible tomato hybrids, and genetic segregation using F2 population derived from a commercial resistant hybrid AG208. With the use of bioinformatics and DNA sequencing analysis tools, deletion of 10 nucleotides was observed in Ty-3 gene sequence for susceptible tomato variety. ACY is a co-dominant indel-based marker that produced clear and strong polymorphic band patterns for resistant plant distinguishing it from its susceptible counterpart. The obtained result correlates with 3:1 segregation ratio of single resistant dominant gene inheritance, which depicted ACY as gene-tag functional marker. This marker is currently in use for screening 968 hybrids varieties and one thousand breeding lines of tomato varieties stocked in Jiangsu Green Port Modern Agriculture Development Company (Green Port). So far, ACY has been used to identify 56 hybrids and 51 breeding lines. These newly detected breeding lines were regarded as potential source of resistance for tomato breeding. This work exploited the sequence of Ty-3 and subsequently contributed to the development of molecular marker ACY to aid phenotypic selection. We thus recommend this marker to breeders, which is suitable for marker-assisted selection in tomato.

Comparative Analyses of Tomato yellow leaf curl virus C4 Protein-Interacting Host Proteins in Healthy and Infected Tomato Tissues

Tomato yellow leaf curl virus (TYLCV), a member of the genus Begomovirus, is one of the most important viruses of cultivated tomatoes worldwide, mainly causing yellowing and curling of leaves with stunting in plants. TYLCV causes severe problems in sub-tropical and tropical countries, as well as in Korea. However, the mechanism of TYLCV infection remains unclear, although the function of each viral component has been identified. TYLCV C4 codes for a small protein involved in various cellular functions, including symptom determination, gene silencing, viral movement, and induction of the plant defense response. In this study, through yeast-two hybrid screenings, we identified TYLCV C4-interacting host proteins from both healthy and symptom-exhibiting tomato tissues, to determine the role of TYLCV C4 proteins in the infection processes. Comparative analyses of 28 proteins from healthy tissues and 36 from infected tissues showing interactions with TYLCV C4 indicated that TYLCV C4 mainly interacts with host proteins involved in translation, ubiquitination, and plant defense, and most interacting proteins differed between the two tissues but belong to similar molecular functional categories. Four proteins-two ribosomal proteins, S-adenosyl-L-homocysteine hydrolase, and 14-3-3 family protein-were detected in both tissues. Furthermore, the identified proteins in symptom-exhibiting tissues showed greater involvement in plant defenses. Some are key regulators, such as receptor-like kinases and pathogenesis-related proteins, of plant defenses. Thus, TYLCV C4 may contribute to the suppression of host defense during TYLCV infection and be involved in ubiquitination for viral infection.

Evaluation of recombinase polymerase amplification for detection of begomoviruses by plant diagnostic clinics

BACKGROUND

Plant viruses in the genus Begomovirus, family Geminiviridae often cause substantial crop losses. These viruses have been emerging in many locations throughout the tropics and subtropics. Like many plant viruses, they are often not recognized by plant diagnostic clinics due in large part to the lack of rapid and cost effective assays. An isothermal amplification assay, Recombinase polymerase amplification (RPA), was evaluated for its ability to detect three begomoviruses and for its suitability for use in plant diagnostic clinics. Methods for DNA extraction and separation of amplicons from proteins used in the assay were modified and compared to RPA manufacturer's protocols. The modified RPA assays were compared to PCR assays for sensitivity, use in downstream applications, cost, and speed.

RESULTS

Recombinase polymerase amplification (RPA) assays for the detection of Bean golden yellow mosaic virus, Tomato mottle virus and Tomato yellow leaf curl virus (TYLCV) were specific, only amplifying the target viruses in three different host species. RPA was able to detect the target virus when the template was in a crude extract generated using a simple inexpensive extraction method, while PCR was not. Separation of RPA-generated amplicons from DNA-binding proteins could be accomplished by several methods, all of which were faster and less expensive than that recommended by the manufacturer. Use of these modifications resulted in an RPA assay that was faster than PCR but with a similar reagent cost. This modified RPA was the more cost effective assay when labor is added to the cost since RPA can be performed much faster than PCR. RPA had a sensitivity approximate to that of ELISA when crude extract was used as template. RPA-generated amplicons could be used in downstream applications (TA cloning, digestion with a restriction endonuclease, direct sequencing) similar to PCR but unlike some other isothermal reactions.

CONCLUSIONS

RPA could prove useful for the cost effective detection of plant viruses by plant diagnostic clinics. It can be performed in one hour or less with a reagent cost similar to that of PCR but with a lower labor cost, and with an acceptable level of sensitivity and specificity.

Aboveground Whitefly Infestation Modulates Transcriptional Levels of Anthocyanin Biosynthesis and Jasmonic Acid Signaling-Related Genes and Augments the Cope with Drought Stress of Maize

Up to now, the potential underlying molecular mechanisms by which maize (Zea mays L.) plants elicit defense responses by infestation with a phloem feeding insect whitefly [Bemisia tabaci (Genn.)] have been barely elucidated against (a)biotic stresses. To fill this gap of current knowledge maize plants were infested with whitefly and these plants were subsequently assessed the levels of water loss. To understand the mode of action, plant hormone contents and the stress-related mRNA expression were evaluated. Whitefly-infested maize plants did not display any significant phenotypic differences in above-ground tissues (infested site) compared with controls. By contrast, root (systemic tissue) biomass was increased by 2-fold by whitefly infestation. The levels of endogenous indole-3-acetic acid (IAA), jasmonic acid (JA), and hydrogen peroxide (H₂O₂) were significantly higher in whitefly-infested plants. The biosynthetic or signaling-related genes for JA and anthocyanins were highly up-regulated. Additionally, we found that healthier plants were obtained in whitefly-infested plants under drought conditions. The weight of whitefly-infested plants was approximately 20% higher than that of control plants at 14 d of drought treatment. The drought tolerance-related genes, ZmbZIP72, ZmSNAC1, and ZmABA1, were highly expressed in the whitefly-infected plants. Collectively, our results suggest that IAA/JA-derived maize physiological changes and correlation of H₂O₂ production and water loss are modulated by above-ground whitefly infestation in maize plants.

High genetic homogeneity points to a single introduction event responsible for invasion of Cotton leaf curl Multan virus and its associated betasatellite into China

BACKGROUND

Cotton leaf curl Multan virus (CLCuMuV) is a Whitefly Transmitted Geminivirus (WTG) endemic to the India subcontinent and is notorious as a causal agent of cotton leaf curl disease (CLCuD), a major constraint to cotton production in south Asia. We found CLCuMuV infecting Hibiscus rosa-sinensis in Guangzhou, China in 2006. The spread and evolution of the invading CLCuMuV were monitored in the following nine years.

FINDINGS

CLCuMuV spread rapidly in the last nine years and became established in Southern China. It infects at least five malvaceous plant species, H. rosa-sinensis, H. esculentus, Malvaiscus arboreus, Gossypium hirsutum and H. cannabinus. Complete nucleotide sequences of 34 geographically and/or temporally distinct CLCuMuV isolates were determined and analyzed together with six other publicly available genomes of CLCuMuV occurring in China. The 40 CLCuMuV isolates were found to share > 99 % nucleotide sequence identity with each other. In all cases tested, the CLCuMuVs were associated with a CLCuMuB. The 36 CLCuMuBs (30 sequenced by us) shared > 98 % nucleotide sequence identity.

CONCLUSION

The high genetic homogeneity of CLCuMuV and CLCuMuB in China suggests the establishment of them from a single founder event.

Plant-mediated whitefly-begomovirus interactions: research progress and future prospects

Plant-mediated interactions between begomoviruses and whiteflies exert important influences on the population dynamics of vectors and the epidemiology of plant diseases. In this article, we synthesize the relevant literature to identify patterns to the interactions. We then review studies on the ecological, biochemical and molecular mechanisms underlying the interactions and finally elaborate on the most interesting issues for future research. The interactions between begomoviruses and the insect vector, the whitefly Bemisia tabaci, via their shared host plants can be mutualistic, neutral or negative. However, in contrast to a pattern of improved performance of vectors on virus-infected plants that has been observed with persistently transmitted RNA viruses, the number of cases exhibiting mutualistic, neutral or negative effects in the indirect interactions between begomoviruses and whiteflies appear evenly distributed. With regard to the mechanisms of plant-mediated positive effects on whiteflies, two case studies indicate that suppression of plant defence and/or alteration in plant nutrition as a result of virus infection can be important. Our review shows that we are only just beginning to understand the tripartite interactions between begomoviruses, whiteflies and plants. Future efforts in this area should try to expand the number and diversity of pathosystems for investigation to reveal the patterns of interactions, to investigate the molecular and biochemical mechanisms of the interactions using a multidisciplinary approach, and to examine the virus-plant-vector interactions in the field and in natural plant communities.