Cucumber Mosaic Virus Isolates Research Articles

Biological, Serological and Molecular Characterization of Cucumber mosaic virus (CMV) Infecting Cucurbita moschata (Duchene ex. Poir) (Summer Squash) in Itu and Uyo Local Governments Areas, Akwa Ibom State, Nigeria

Cucurbita moschata is an edible member of the family Cucurbitaceae. The plant is commonly observed showing typical virus-like symptoms during the growing season in Akwa Ibom State, Nigeria. A total of 7 leaf samples showing typical virus-like symptoms were collected from C. moschata in different locations in Itu and Uyo Local Government, Akwa Ibom State. All the virus isolates used in this study were sap transmissible with a wide host range. The virus isolates irrespective of the place of collection were transmitted in a fore-gut manner by A. spiraecola. Aphis citricida did not transmit the viruses. All the virus isolates reacted positively to cucumovirus polyclonal antibody in antigen coated plate-ELISA (ACP-ELISA). Gel electrophoresis of the cDNA of the virus isolates produced 500 base pairs typical of Cucumber mosaic virus. The gene sequence analysis revealed that all the isolates had sequence homology of 95% and above with Cucumber mosaic virus (CMV) and are therefore considered strains of CMV. The results also showed that CMV isolates investigated in this study shared common ancestry, though belonging to different clusters. The results also indicated that CMV could be widespread and therefore a threat to C. moschata production in Itu and Uyo Local Government Areas of Akwa Ibom State. This is the first report of CMV infecting C. moschata in Akwa Ibom State, Nigeria. Further work should be carried out to cover the entire state.

Characterization of Cucumber Mosaic Virus Isolated from Passion Fruit (<ii>Passiflora edulis) in Korea

In July 2020, total RNA was extracted from passion fruit (<i>Passiflora edulis</i>) leaves showing virus symptoms such as chlorotic spots and vein banding in Haenam, South Korea. Cucumber mosaic virus (CMV)-HN2 was identified through reverse transcription polymerase chain reaction and sequencing analysis. To confirm the biological characteristics of the CMV infecting passion fruit, 10 indicator plants were inoculated with CMV-HN2, and the results showed a typical CMV symptoms. Phylogenetic analysis based on the amino acid of the coat protein (CP) of CMVs revealed that the CMV passion fruit isolates belonged to subgroup I, among which CMV-HN2 belonged to subgroup IA. Additionally, CMVs isolated from passion fruit in Korea have amino acid sequence variation between the subgroup. Among them, CMV-HN2 had four to eight amino acid differences in CP from other CMV isolates from passion fruit. These results confirm the presence of genetic diversity in the CPs of passion fruit CMV isolates.

Natural occurrence of cucumber mosaic virus infecting Adenium obesum plants in Brazil

AbstractIn 2022, virus‐like symptoms were observed in Adenium obesum plants in Brazil. High‐throughput sequencing analysis found three contig sequences of cucumber mosaic virus (CMV) genome segments, which were of 3352, 3006 and 2221 nucleotides, and shared 98.59%, 95.02% and 98.05% nucleotide identities with the nucleotide sequences of CMV RNAs 1, 2 and 3, respectively. Phylogenetic analysis of the coat protein gene indicated that the CMV isolate belongs to the subgroup IB. Symptoms of mottle like those observed in the field samples were reproduced on mechanically inoculated plants of A. obesum, and RT‐PCR confirmed the CMV infection. CMV was transmitted by Aphis gossypii to A. obesum plants. This is the first report of CMV infecting A. obesum plants in Brazil.

İzmir’den Alınan Hıyar mozaik virüsü (CMV) İzolatlarının Biyolojik ve Moleküler Tespiti

Objective: This study was intended to determine cucumber mosaic virus (CMV) isolates present in tomato-growing areas of the Izmir province of Turkey in 2021-2022 based on mechanical inoculations and RT-PCR method.
 Materials and Methods: 17 CMV suspected plant samples previously obtained from Izmir between 2019-2022 and preserved under the appropriate temperature in the Faculty of Agriculture, Department of Plant Protection of Ege University were used to carry out mechanical inoculation of the virus into a number of different test plants consisting of Nicotiana glutinosa, Solanum lycopersicum ‘SC-2121’, and Cucumis sativus ‘Beit Alpha’ cultivars. Virus-inoculated plants were visually evaluated for symptom development, followed by a DAS-ELISA test with CMV-specific antibodies. CMV-positive tobaccos were used to repeat mechanical inoculation of the virus into newly grown test plants, followed by a second ELISA and final RT-PCR test.
 Results: As a result, CMV-D and CMV-B2 isolates obtained from Izmir produced CMV-like symptoms in the test plants. However, only CMV-D inoculated test plants consistently came out to be positive in the final ELISA and RT-PCR test. CMV-D isolate in tobacco and cucumber induced systemic mosaic and in tomato, caused mosaic, stunting and bushy appearance during 3 weeks of virus inoculation. CMV-D inoculated plants when tested for RT-PCR produced an amplified cDNA band of 280 bp in agarose gel indicating the presence of the virus.
 Conclusion: This study concludes that CMV causes a variety of symptoms depending upon the viral strain involved, infected host species, and other factors. The presence of CMV-D isolate has been biologically and molecularly identified based on repeated mechanical inoculations in its host species and a final RT-PCR test performed under a controlled experimental setup. Further study of the responsible isolate can be achieved by its genome sequencing and phylogenetic analysis to better understand the viral strain involved in the infection.

Seed Transmission of an Indian Isolate of Cucumber Mosaic Virus Infecting Chilli (Capsicum annuum L.)

Chilli (Capsicum annuum. L) is an economically valuable spice crop worldwide and Cucumber mosaic virus (CMV) is the major constraint for its production. To study its seed transmissibility nature, the chilli seedlings were sap-inoculated with CMV isolate (CMV-TSWA) from Warangal district, Telangana and raised under insect proof glasshouse condition until seed production. The CMV-infected plants developed mosaic, mottling, deformation, systemic infection, stunted appearance, delayed flower formation, deformed fruit production and reduced seed production compared to uninfected healthy plants. The virus was detected in the leaves, flowers, green fruit, dry pericarp and seeds of sap-inoculated chilli plants by DAC-ELISA and the percentage of detection was 83.33% in leaves, 46.66% in flowers, 20% in fruits, 16.66% in pericarp of dried chilli and 13.33% in seeds. Seedlings emerged from the infected seeds initially showed mottling and wrinkling of leaves, which further intensified as leaf deformation and stunted appearance compared to healthy ones, and the presence of CMV was confirmed by DAC-ELISA. CMV is seed-borne in chilli and transmitted from seed to seedlings and the rate of transmission was 9% as determined by grow-out test and DAC-ELISA.

Effect of Cucumber mosaic virus on the Content of Some Melon Genotypes of Some Mineral Elements and Plant Hormones

This study was conducted to determine the effect of cucumber mosaic virus (CMV) infection on the levels of some mineral elements and plant hormones in some melon genotypes. All experiments mentioned in this research were conducted in the Laboratory of plant virology and Greenhouses belonging to the Plant Protection Department/ College of the Agriculture/ University of Kerbala. PCR amplification using the complementary DNA (cDNA), synthesized from RNA isolated from an infected plant, produced a 650bp PCR product. A BLAST search using the nucleotide sequence of the PCR product demonstrated that this CMV isolate was previously registered at the National Centre for Biotechnology Information (NCBI) with a similarity of 100% with some CMV isolates identified in Hungary (AJ517802), Australia (U22821), and Slovenia (OL142046). It was also found that all melon genotypes evaluated in this study were susceptible to CMV, and the genotypes HA-144 and HA-609 were the most susceptible to CMV among the other tested genotypes. Results also showed that the CMV infection significantly reduced the levels of some minerals (calcium, magnesium, and manganese), and the genotypes HA-144, GM-3034, and GA-1534 were the most affected by the virus.; whereas the mineral elements sodium and potassium were significantly increased in their levels in infected plants, especially in the genotype HA-609. The CMV infection also clearly reduced the level of the hormone gibberellin in genotypes and the GA-1534 genotype was the most impacted and significantly different from their levels in the uninfected plants. However, the CMVinfected genotypes showed a significant increase in the level of the hormones cytokinin.

Absence of Seed-Mediated Transmission of Cucumber Mosaic Virus in Espelette Pepper Crops despite Widespread and Recurrent Epidemics.

In the past decade, severe epidemics of cucumber mosaic virus (CMV) have caused significant damage to Espelette pepper crops. This virus threatens the production of Espelette pepper, which plays a significant role in the local economy and touristic attractiveness of the French Basque Country, located in southwestern France. In 2021 and 2022, CMV was detected via double-antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISAs) in Gorria pepper seed lots harvested from naturally infected fields scattered throughout the entire Espelette pepper production area. These seed lots were used in greenhouse grow-out tests to determine whether CMV could be transmitted to seedlings from contaminated seeds, using visual symptom assessment, DAS-ELISAs, and reverse transcription-polymerase chain reaction (RT-PCR). Despite the widespread occurrence of CMV in seeds of field samples, the grow-out experiments on a total of over 5000 seedlings yielded no evidence of seed transmission of local CMV isolates in Gorria pepper. Therefore, rather than seeds from infected pepper plants, sources of CMV inoculum in Espelette are more likely to be alternative hosts present in and around pepper fields that can allow for the survival of CMV during the off-season. These results have important epidemiological implications and will guide the choice of effective measures to control current epidemics.

Genome sequencing of cucumber mosaic virus (CMV) isolates infecting chilli and its interaction with host ferredoxin protein of different host for causing mosaic symptoms.

The online version contains supplementary material available at 10.1007/s13205-023-03777-8.

Vasconcellea cauliflora – a new natural host of cucumber mosaic virus

Vasconcellea cauliflora plants exhibiting chlorotic spots, mottling and mosaic with yellowing on leaves were observed in Pune, India in October 2020. The disease incidence was 16%. The samples were screened for cucumber mosaic virus (CMV), papaya ringspot virus, tobacco mosaic virus and zucchini yellow mosaic virus using ELISA. Sap inoculation on healthy V. cauliflora plants using CMV positive DAS-ELISA samples reproduced field symptoms. The transmission upon mechanical inoculation was 100%. For further confirmation, RT-PCR was carried out using CMV coat protein gene specific primers. Amplicons of expected size (c. 650 bp) were obtained in all symptomatic and sap inoculated samples. No amplification was observed in the asymptomatic samples. BLASTn analysis revealed that the amplicon sequence shares more than 99% identity with CMV isolates and in phylogenetic analysis it clustered with CMV IB isolates. This is the first record of V. cauliflora as a natural host of CMV worldwide.

Genomic characterization of recombinant cucumber mosaic virus isolates infecting mustard species via HTS in India

AbstractOne of the most pervasive plant viruses, the cucumber mosaic virus (CMV), Bromoviridae: Cucumovirus, infects a variety of plants worldwide and significantly affects production quality and quantity. Viral infection exhibiting severe mosaic and stunting symptoms in plants infected with turnip mosaic virus was observed in experimental fields in IARI. Leaf samples were collected and the virome was identified through high‐throughput sequencing subjecting ribosomal RNA‐depleted mRNA. Here, we unravel for the first time the complete genome sequences of two CMV isolates infecting yellow and black‐seeded mustard in India. The three segments of the viral genome, as well as coat protein cds, were amplified and subjected to Sanger sequencing. The three viral genomic components were 3348 of RNA1, 3032 and 3040 of RNA2, 2260 and 2236 nts of RNA 3, respectively (including the 5′ and 3′ UTR). The two isolates shared high sequence identity and clubbed with the subgroup‐IB isolates in a clade. Recombination signals were detected within all the three RNAs of both New Delhi isolates wherein one of the parent isolates was reported to infect the family Brassicaceae. Recombination was observed throughout the region of RNA2 but the 3′ UTR was observed to be most prone to recombination. This is the first comprehensive depiction of a recombinant CMV subgroup IB isolate from black, yellow and brown‐seeded mustard from India, which has implications for its robust detection and overall management. This study also provides insight into population structuring, host expansions, level of genetic heterogeneity and variability of worldwide prevalent CMV isolates.

İzmir ilinde domates ve biber bitkilerini etkileyen tomato spotted wilt virus (TSWV) ve cucumber mosaic virus (CMV) etmenlerinin moleküler karakterizasyonu

Objective: The objective of this study was to investigate tomato spotted wilt virus (TSWV) and cucumber mosaic virus (CMV) infections in tomato and pepper plants showing virus-induced symptoms in vegetable growing districts of İzmir, Turkey. Material and Methods: Surveys were carried out in tomato and pepper plantations in 2019 and 2021, and the incidences of these viruses in the collected leaf samples were determined by RT-PCR. Nucleotide identities and phylogenetic relationships of the TSWV and CMV isolates with other isolates retrieved from the GenBank database were determined. Results: The results of this study showed that tomato plants were infected at the same rate (21.50%) with TSWV and CMV. Out of the tested pepper samples, 64.15% were infected with TSWV and 25.47% with CMV. The results showed that, the identity rate of nucleoprotein region of TSWV isolates from tomato was 99-96% at nucleotide level while the isolates from pepper showed 100-95% identity. On the other hand, the capsid protein gene region of the tomato isolate of CMV had nucleotide identity rate of 98-95% with other isolates in GenBank, while that of its pepper isolates had 100-98% identity. Also, CMV isolates of this study showed close phylogenetic relationship with the CMV isolates of subgroup IB. Conclusion: This study revealed the prevalence of TSWV and CMV in symptomatic tomato and pepper samples in İzmir province and some molecular properties of them.

Incidence and detection of cucurbit mosaic disease in Assam

The cucurbits belong to the family Cucurbitaceous (gourd family) under the order Cucurbit ales which include many economically important vegetable and fruit species. Among various factors, viruses are one of the important factors reducing in quantity as well as quality of cucurbits. These crops are severely affected by the cucurbit mosaic disease worldwide, which is the major viral disease of the cucurbits. Considering the importance of the disease, the present investigation was taken up for incidence, detection, host range study and characterization of viruses associated with cucurbit mosaic disease in Assam. Survey was conducted in 5 districts of Assam (Sonitpur, Biswanath, Jorhat, Sivasagar, Dibrugarh) during 2021-22. Symptomatology revealed presence of various mosaic symptoms in the surveyed areas. Among the five surveyed locations, the symptoms observed in Sonitpur district were severe, whereas Biswanath district were moderate and mild symptoms were observed in Jorhat, Sivasagar, and Dibrugarh districts. Vector incidence study showed that aphid is the predominant vector. Molecular assay confirmed the presence of Cucumber Mosaic Virus in the collected cucurbit samples of surveyed areas; with severe incidence of mosaic disease in Sonitpur (90.91%), moderate in Biswanath (66.67%), mild in Jorhat (14.29%), Sivasagar (11%) and Dibrugarh (25%) districts. Molecular characterization of Cucumber mosaic virus cucurbit isolate from Jorhat district of Assam, was done through partial sequencing and similarity analysis showed 90.94 to 94.74 per cent sequence homology with different worldwide isolates of Cucumber mosaic virus.

Serologic and molecular determination and phylogenetic analysis of some viruses infecting pepper in Turkey

Viruses are among the major agents causing yield loss in pepper production. During the 2016-2017, a survey was performed in pepperfields to determine of some viruses in pepper plants showing virus-like symptoms in different provinces of Turkey. Plant samples wereassayed using DAS-ELISA with specific antisera for cucumber mosaic virus (CMV), tomato spotted wilt virus (TSWV), tomato yellow leafcurl virus (TYLCV), alfalfa mosaic virus (AMV), and pepper mild mottle virus (PMMoV). The DAS-ELISA results indicated that 42.2, 17.5,17.5, and 10.6 of the 421 samples were infected with CMV, TSWV, AMV, and PMMoV, respectively. The positive samples were furtheranalysed by RT-PCR and sequencing. Based on sequence analyses, a phylogenetic tree was drawn for each of CMV, PMMoV and AMV.Phylogenetic analysis showed that CMV isolates were placed in subgroup IA within the major group I. The AMV isolates were classifiedwithin four clades and showed a high variability. PMMoV isolates were grouped with Serbia, Brazil, and Japan isolates within the group I.One AMW isolates determined possible recombinant isolates. Further studies needed for more information about recombinant isolatesand evolutions. The analyses of the molecular structure of viruses is important for the accurate diagnosis of the pathogen and to applythe right method of management strategies for controlling plant viruses in agriculture.

Molecular characterization and differentiation of cucumber mosaic virus subgroups in Serbia by RT-PCR-RFLP

Samples of various host plants from different locations in Serbia showing foliar symptoms resembling those caused by the cucumber mosaic virus (CMV) were collected. Samples were considered CMV-infected after detection by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Fifteen CMV isolates were selected for developing a reverse transcription-polymerase chain reaction (RT-PCR) restriction fragment length polymorphism (RFLP) protocol and a more detailed molecular characterization of all five genes. Based on in silico RFLP, the following restriction enzymes were selected: HindIII, SacII (1a gene), MluI (2a gene), StuI, SalI (2b gene), BaeI (movement protein (MP) gene of CMV), SfcI, and HaeIII (capsid protein (CP) gene), which were capable of distinguishing between subgroups of CMV based on the obtained characteristic restriction patterns. According to in situ RFLP, the predominant haplotype IA; IA, IA; IA, IA was determined in 14, while the distinct haplotype II; II, II; II, II was found in only one isolate. Sequence analyses of two selected Serbian CMV isolates with different restriction patterns and haplotype profiles confirmed the RFLP results, showing that isolates 674-11 and 137-13 belong to subgroups IA and II, respectively. Different restriction patterns after digestion of all five CMV genomic regions proved to be a simple way to investigate the natural population of CMV. This study provides insight into the genetic structure of the CMV population in Serbia.

Effects of Cucumber Mosaic Virus on Yield Components and Yield of Bambara Groundnut

Bambara groundnut (Vigna subterranean L. Verdc) is a leguminous plant and its seeds are highly nutritious and can be considered as complete food. In addition to being a neglected crop; its production is limited by several constraints among which virus diseases are the most implicated. In order to contribute to the improvement of bambara groundnut in Nigeria, landraces of bambara groundnut were screened for resistance to Cucumber mosaic virus (CMV), one of the most damaging viruses in grain legumes. Treatments consisted of five landraces namely Black, Brown, Cream, Red nav, and Zebra coloured got from local farmers. These were arranged in Randomised Complete Block Design, with three replicates. Seedlings were infected with CMV isolate three weeks after sowing (WAS), during the 2019 and 2020 trials. The infected plants exhibited various symptoms of chlorosis, leaf deformation, growth retardation, and plant stunting. The sCMV caused significant reduction in plant height, the number of branches, leaves, pods, and seeds weight. In the 2019 and 2020 trials, 100 % incidence with the highest severity was observed in the Bambara groundnut landraces. Disease incidence varied between 41.6% in “Black” and 95.8 % in “Cream,” while disease severity was higher in “Cream” and “Red nav” with 5.0 respectively. “Black” and “Zebra” were the tallest with 16.8 cm among the infected as well as disease-free with 22.6 cm tall plants. “Black” landrace produced the highest number of pods in both CMV infections with 21 and disease-free with 33 pods respectively. Conversely, the number of days to flowering of 43 days was highest in infected plants of “Black”. The “Black” and “Zebra” landraces recorded uniform seed weights and the highest seed weight under CMV infection with 1.7 g per plant. The impact of the virus on yield loss was lowest in “Black” and “Zebra” landraces which indicated their possible use in the management of Cucumber mosaic virus disease in Bambara groundnut.

Occurrence and Molecular Variability of the Main Kiwifruit Viruses in the Sichuan Province of China.

Viruses cause important yield losses in kiwifruit. Here, we studied the occurrence and population structure of the major kiwifruit viruses in the Sichuan province of China. RT-PCR results showed the presence of Actinidia virus A (AcVA), Actinidia virus B (AcVB), Actinidia chlorotic ringspot-associated virus (AcCRaV), and the cucumber mosaic virus (CMV). AcCRaV was widely distributed, followed by CMV. These two viruses were often detected in co-infection with AcVA and AcVB. The virus detection rate was positively correlated with vine age. Four phylogenetic groups of AcVA and AcVB were identified, with AcVA isolates clustering mainly in subgroup I, and AcVB isolates clustering mainly in subgroups II, III, and IV. All CMV isolates clustered in subgroup II, and AcCRaV isolates clustered in subgroup IA. The genome of AcVA and AcCRaV was under negative selection pressure, while the genome of AcVB and CMV was under positive selection pressure. All the viruses, except AcVB, were in a state of expansion. The full-length genome of the most widely distributed AcCRaV isolate in kiwifruits in the Sichuan province was characterized by sequencing. Unique eight-nucleotide (TTTTTGAT) repeats were found in the 5'-terminal non-coding region of the AcCRaV RNA3 in a possible association with reduced disease symptoms. This is the first study of kiwifruit viruses in Sichuan.

Defense Responses and Metabolic Changes Involving Phenylpropanoid Pathway and PR Genes in Squash (Cucurbita pepo L.) following Cucumber mosaic virus Infection

The current study focuses on the effects of Cucumber mosaic virus (CMV) infection on phytochemical changes and pathogenesis- and phenylpropanoid pathway-associated gene activities in squash (Cucurbita pepo L.) plants during a time course of 2 to 12 days post inoculation (dpi). The identity of the CMV isolate was confirmed by DAS-ELISA, TEM, and coat protein gene sequence. The CMV infection initially boosts and then suppresses transcript levels of the defense-related genes PR-1, PR-2, PAL, HQT, and CHS during the investigated time course compared to controls. The expression profile during the time-course study indicated that early, transient induction of PR-1 occurs during CMV infection, while CMV induced the expression of PR-2 in systemically infected squash tissues at all time points and suppressed the expression of PAL and HQT at 8-12 dpi. CHS transcript levels fluctuated between up- and down-regulation, but by 12 dpi, CHS expression reached its peak. The HPLC and GC–MS analyses of CMV-infected squash extracts revealed that different phenolic, flavonoid, and fatty acid compounds could be induced or suppressed upon CMV infection. In particular, CMV could suppress the synthesis of most phenolic compounds, specifically chlorogenic acid, possibly leading to the virus’s rapid spread.

High-Throughput Sequencing Discloses the Cucumber Mosaic Virus (CMV) Diversity in Slovakia and Reveals New Hosts of CMV from the Papaveraceae Family.

Cucumber mosaic virus (CMV; Cucumovirus, Bromoviridae) is an omnipresent virus characterized by a large host range and high genetic variability. Using high-throughput sequencing, we have characterized near complete genomes of 14 Slovak CMV variants from different plant hosts. Of these, three variants originated from the Papaveraceae species (oilseed poppy, common poppy and great celandine), previously poorly described as CMV natural hosts. Based on a BLAST search and phylogenetic analysis, the Slovak CMV isolates can be divided into two genetically different Groups, Ia and II, respectively. The SL50V variant, characterized by a divergent RNA2 sequence, potentially represents a reassortant variant. In four samples (T101, SL50V, CP2, MVU2-21), the presence of satellite CMV RNA was identified along with CMV. Although mechanically transmitted to experimental cucumber plants, the role of satellite RNA in the symptomatology observed could not be established due to a complex infection of original hosts with different viruses.

Preponderance of mixed infection of Cucumber mosaic virus and Candidatus Phytoplasma australasia on brinjal in India

Cucumber mosaic virus (CMV) has broad host range by infecting major stable food crops and causes heavy loss especially in brinjal. In major brinjal growing tracts of Tamil Nadu, Krishnagiri recorded the highest combined infection of CMV and Candidatus Phytoplasma australasia (Ca. P. australasia) with 26%. The symptoms ranged from mild to severe mosaic, mottling, filiformity of leaves and little leaf. The virus was successfully transmitted to cowpea cv. CO7 and ridge gourd through mechanical inoculation and the presence of virus was detected both by DAC-ELISA and RT-PCR. Electron microscopy of CMV exemplified isometric particles with 28–35 nm under TEM and phytoplasma with 700–820 nm in SEM analysis. Among the different test hosts, Luffa acutangula was found to be the best indicator host for brinjal CMV isolate as it requires shorter period (4-5DPI) to express symptoms with good virus titer (A405nm 2.318). The genome characterization of CMV TNB isolate revealed that the RNA1, RNA2 and RNA3 have 97, 96 and 99% homology with other 1B sub group CMV isolates, respectively. Recombination analysis of RNA2 of CMV TNB has tomato Egyptian isolate (KT921315) as major parent and black pepper Indian isolate (KU947030) as minor parent at the conserved region (52-805nt). The characterization of phytoplasma using iphy classifier reveled Ca. P. australasia belonging to 16SrIID subgroup was present along with CMV infection. In addition, the Solanum torvum grown in and around brinjal ecosystem showed severe mosaic and exhibited 99% nucleotide identity with CMV TNB isolate and these plants also act as inoculum source during the on and off cropping season in India. To our knowledge this is the first record of mixed infection of CMV and Ca. P. australasia in brinjal and first record of CMV infection in S. torvum in India.

Cucumber Mosaic Virus Infection in Arabidopsis: A Conditional Mutualistic Symbiont?

A cucumber mosaic virus isolate, named Ho [CMV(Ho)], was isolated from a symptomless Arabidopsis halleri field sample containing low virus titers. An analysis of CMV(Ho) RNA molecules indicated that the virus isolate, besides the usual cucumovirus tripartite RNA genome, additionally contained defective RNA3 molecules and a satellite RNA. To study the underlying mechanism of the persistent CMV(Ho) infection in perennial A. halleri, infectious cDNA clones were generated for all its genetic elements. CMV, which consists of synthetic transcripts from the infectious tripartite RNA genomes, and designated CMV(Ho)tr, multiplied in A. halleri and annual Arabidopsis thaliana Col-0 to a similar level as the virulent strain CMV(Y), but did not induce any symptoms in them. The response of Col-0 to a series of reassortant CMVs between CMV(Ho)tr and CMV(Y) suggested that the establishment of an asymptomatic phenotype of CMV(Ho) infection was due to the 2b gene of CMV RNA2, but not due to the presence of the defective RNA3 and satellite RNA. The accumulation of CMV(Ho) 2b protein tagged with the FLAG epitope (2b.Ho-FLAG) in 2b.Ho-FLAG-transformed Col-0 did not induce any symptoms, suggesting a 2b-dependent persistency of CMV(Ho)tr infection in Arabidopsis. The 2b protein interacted with Argonaute 4, which is known to regulate the cytosine methylation levels of host genomic DNA. Whole genomic bisulfite sequencing analysis of CMV(Ho)tr- and mock-inoculated Col-0 revealed that cytosine hypomethylation in the promoter regions of 82 genes, including two genes encoding transcriptional regulators (DOF1.7 and CBP1), was induced in response to CMV(Ho)tr infection. Moreover, the increased levels of hypomethylation in the promoter region of both genes, during CMV(Ho)tr infection, were correlated with the up- or down-regulation of their expression. Taken altogether, the results indicate that during persistent CMV(Ho) infection in Arabidopsis, host gene expression may be epigenetically modulated resulting from a 2b-mediated cytosine hypomethylation of host genomic DNA.