Naturally occurring substitution of an amino acid in a plant virus gene-silencing suppressor enhances viral adaptation to increasing thermal stress.

Cereal yellow dwarf virus (CYDV-RPV) encodes a P0 protein that functions as a viral suppressor of RNA silencing (VSR). The strength of silencing suppression is highly variable among CYDV-RPV isolates. In this study, comparison of the P0 sequences of CYDV-RPV isolates and mutational analysis identified a single C-terminal amino acid that influenced P0 RNA-silencing suppressor activity. A serine at position 247 was associated with strong suppressor activity, whereas a proline at position 247 was associated with weak suppressor activity. Amino acid changes at position 247 did not affect the interaction of P0 with SKP1 proteins from Hordeum vulgare (barley) or Nicotiana benthamiana. Subsequent studies found P0 proteins containing a P247 residue were less stable than the P0 proteins containing an S247 residue. Higher temperatures contributed to the lower stability and in planta and the P247 P0 proteins were subject to degradation via the autophagy-mediated pathway. A P247S amino acid residue substitution in P0 increased CYDV-RPV replication after expression in agroinfiltrated plant leaves and increased viral pathogenicity of P0 generated from the heterologous Potato virus X expression vector system. Moreover, an S247 CYDV-RPV could outcompete the P247 CYDV-RPV in a mixed infection in natural host at higher temperature. These traits contributed to increased transmission by aphid vectors and could play a significant role in virus competition in warming climates. Our findings underscore the capacity of a plant RNA virus to adapt to climate warming through minor genetic changes in gene-silencing suppressor, resulting in the potential for disease persistence and prevalence.

Metatranscriptome analysis of symptomatic bitter apple plants revealed mixed viral infections with a putative novel polerovirus.

BACKGROUND: Next-generation Sequencing (NGS) combined with bioinformatic analyses constitutes a powerful approach for identifying and characterizing previously unknown viral genomes. In this study, leaf samples from bitter apple plants (Citrullus colocynthis (L.) Schrad) exhibiting symptoms such as dwarfing, leaf crinkling, and chlorosis were collected from the southern part of Kerman province, Iran. RESULTS: Putative infecting viruses were identified through de novo assembly of sequencing reads using various tools, followed by BLAST analysis. Complete genomes for Squash vein yellowing virus (SqVYV), Citrus-associated rhabdovirus (CiaRV), and a novel polerovirus-related strain termed Bitter apple aphid-borne yellows virus (BaABYV) were assembled and characterized. Additionally, a partial genome for Watermelon mosaic virus (WMV) was assembled. The genomic organization of the BaABYV was determined to be 5'-ORF0-ORF1-ORF1,2-ORF3a-ORF3-ORF3,5-ORF4-3'. Amino acid sequence identities for inferred proteins (P0 and P1, P1,2) with known poleroviruses were found to be the 90% species delineation limit, implying that BaABYV should be considered a new member of the genus Polerovirus. Recombination events were observed in the BaABYV and WMV strains; such events were not found in the CiaRV strain. CONCLUSIONS: Molecular evidence from this study suggests that C. colocynthis is a reservoir host of several plant viruses. Among them, BaABYV is proposed as a new member of the genus Polerovirus. Furthermore, the CiaRV strain has been reported for the first time from Iran.

Recessive resistance against beet chlorosis virus is conferred by the eukaryotic translation initiation factor (iso)4E in Beta vulgaris.

Eukaryotic translation initiation factors (eIFs) are important for mRNA translation but also pivotal for plant-virus interaction. Most of these plant-virus interactions were found between plant eIFs and the viral protein genome-linked (VPg) of potyviruses. In case of lost interaction due to mutation or deletion of eIFs, the viral translation and subsequent replication within its host is negatively affected, resulting in a recessive resistance. Here we report the identification of the Beta vulgaris Bv-eIF(iso)4E as a susceptibility factor towards the VPg-carrying beet chlorosis virus (genus Polerovirus). Using yeast two-hybrid and bimolecular fluorescence complementation assays, the physical interaction between Bv-eIF(iso)4E and the putative BChV-VPg was detected, while the VPg of the closely related beet mild yellowing virus (BMYV) was found to interact with the two isoforms Bv-eIF4E and Bv-eIF(iso)4E. These VPg-eIF interactions within the polerovirus-beet pathosystem were demonstrated to be highly specific, as single mutations within the predicted cap-binding pocket of Bv-eIF(iso)4E resulted in a loss of interaction. To investigate the suitability of eIFs as a resistance resource against beet infecting poleroviruses, B. vulgaris plants were genome edited by CRISPR/Cas9 resulting in knockouts of different eIFs. A simultaneous knockout of the identified BMYV-interaction partners Bv-eIF4E and Bv-eIF(iso)4E was not achieved, but Bv-eIF(iso)4EKO plants showed a significantly lowered BChV accumulation and decrease in infection rate from 100% to 28.86%, while no influence on BMYV accumulation was observed. Still, these observations support that eIFs are promising candidate genes for polerovirus resistance breeding in sugar beet.

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.

Genomic variation in pepper vein yellows viruses in Australia, including a new putative variant, PeVYV-10.

Since the first identification and full sequence of the polerovirus pepper vein yellows virus in Australia in 2016, virus surveys of crops and weeds have sporadically identified PeVYV in different hosts and locations. Genomic comparisons of 14 PeVYV-like isolates using RT-PCR products spanning the 3' end of the RdRp region (ORF 2), the intergenic region, ORF 3a, ORF 4, and ORF 3 (1388 nt) showed that four of the PeVYV isolates might be a new variant or PeVYV-like virus. From six PeVYV-positive plants, eight PeVYV-like sequences were obtained by high-throughput sequencing, as two hosts, 5352 and 5634, contained two slightly different PeVYV-like isolates. Three of the PeVYV-like isolates were most closely related to PeVYV-6 and PeVYV-5, and two isolates were closely related to PeVYV-9 and PeVYV-2. The other three isolates shared only 69-74% nucleotide sequence identity across the whole genome with any of the other PeVYVs, despite sharing 73-98%, 87-91%, and 84-87% amino acid sequence identity in ORF 3a, ORF 3, and the RdRp (ORF 2), respectively, suggesting that this virus is a new PeVYV-like virus, which we have tentatively called PeVYV-10. This is also the first report of a PeVYV-like virus infecting garlic.

Complete nucleotide sequence of chrysanthemum virus D, a polero-like virus.

A putative new polerovirus, named "chrysanthemum virus D" (ChVD), was detected in a Chrysanthemum morifolium plant in South Korea. The virus was identified by high-throughput sequencing and confirmed by reverse transcription polymerase chain reaction. The entire ChVD genome is composed of 5,963 nucleotides and contains seven open reading frames (ORF0-5 and ORF3a), which are arranged similarly to those of other poleroviruses. These ORFs encode the putative proteins P0-5 and P3a, respectively. Pairwise amino acid sequence comparisons showed that the ChVD P0-5 and P3a proteins have 30.45-75% sequence identity to the corresponding proteins of other members of the genus Polerovirus. Since one of the species demarcation criteria for the genus Polerovirus is > 10% difference in the amino acid sequence of any gene product, the sequence comparisons indicate that ChVD represents a new species in this genus. Phylogenetic analysis of the P1-P2 and P3 amino acid sequences further indicate that ChVD is a novel polerovirus.

Complete genome characterization of cacao leafroll virus, a newly described cacao-infecting polerovirus.

The complete genome sequence of cacao leafroll virus (CaLRV; family Solemoviridae, genus Polerovirus) was determined by high-throughput sequencing of total RNA isolated from symptomatic cacao Theobroma cacao L. plants (n = 4). The CaLRV genome sequences ranged from 5,976 to 5,997 nucleotides (nt) in length and contained seven open reading frames (ORFs). Nucleotide and amino acid (aa) sequence comparisons showed that, among selected well-characterized poleroviruses, the CaLRV genome shared the highest nt sequence identity of 62% with that of potato leafroll virus (PLRV, NC_076505). A comparison of the predicted aa sequence of the CaLRV coat protein indicated that cotton leafroll dwarf virus (CLRDV, NC_014545) and melon aphid-borne yellows virus (MABYV, NC_010809) were the closest relatives, sharing 57% aa sequence identity. Bayesian phylogenetic analysis based on complete genome sequences showed that CaLRV grouped with well-characterized poleroviruses that cause diseases of cereal and vegetable crops. During the course of publishing this work, the nearly complete genome sequence of a member of the same polerovirus species, referred to as "cacao polerovirus" (OR605721), with which CaLRV shares 99% nt sequence identity, was reported.

Genetic Variability Among U.S.-Sentinel Cotton Plot Cotton Leafroll Dwarf Virus and Globally Available Reference Isolates Based on ORF0 Diversity.

The aphid-transmitted polerovirus, cotton leafroll dwarf virus (CLRDV), first characterized from symptomatic cotton plants in South America, has been identified in commercial cotton plantings in the United States. Here, the CLRDV intraspecific diversity was investigated by comparative sequence analysis of the most divergent CLRDV coding region, ORF0/P0. Bayesian analysis of ORF0 sequences for U.S. and reference populations resolved three well-supported sister clades comprising one U.S. and two South American lineages. Principal component analysis (PCA) identified seven statistically supported intraspecific populations. The Bayesian phylogeny and PCA dendrogram-inferred relationships were congruent. Population analysis of ORF0 sequences indicated most lineages have evolved under negative selection, albeit certain sites/isolates evolved under positive selection. Both U.S. and South American isolates exhibited extensive ORF0 diversity. At least two U.S. invasion foci were associated with their founder populations in Alabama-Georgia and eastern Texas. The Alabama-Georgia founder is implicated as the source of recent widespread expansion and establishment of secondary disease foci throughout the southeastern-central United States. Based on the geographically restricted distribution, spread of another extant Texas population appeared impeded by a population bottleneck. Extant CLRDV isolates represent several putative introductions potentially associated with catastrophic weather events dispersing viruliferous cotton aphids of unknown origin(s).

Genetic Variation of Turnip Yellows Virus in Arable and Vegetable Brassica Crops, Perennial Wild Brassicas, and Aphid Vectors Collected from the Plants.

Turnip yellows virus (TuYV; Polerovirus, Solemoviridae) infects and causes yield losses in a range of economically important crop species, particularly the Brassicaceae. It is persistently transmitted by several aphid species and is difficult to control. Although the incidence and genetic diversity of TuYV has been extensively investigated in recent years, little is known about how the diversity within host plants relates to that in its vectors. Arable oilseed rape (Brassica napus) and vegetable brassica plants (Brassica oleracea), wild cabbage (B. oleracea), and aphids present on these plants were sampled in the field in three regions of the United Kingdom. High levels of TuYV (82 to 97%) were detected in plants in all three regions following enzyme-linked immunosorbent assays. TuYV was detected by reverse transcription polymerase chain reaction in Brevicoryne brassicae aphids collected from plants, and TuYV sequences were obtained. Two TuYV open reading frames, ORF0 and ORF3, were partially sequenced from 15 plants, and from one aphid collected from each plant. Comparative analyses between TuYV sequences from host plants and B. brassicae collected from respective plants revealed differences between some ORF0 sequences, which possibly indicated that at least two of the aphids might not have been carrying the same TuYV isolates as those present in their host plants. Maximum likelihood phylogenetic analyses including published, the new TuYV sequences described above, 101 previously unpublished sequences of TuYV from oilseed rape in the United Kingdom, and 13 also previously unpublished sequences of TuYV from oilseed rape in Europe and China revealed three distinct major clades for ORF0 and one for ORF3, with some distinct subclades. Some clustering was related to geographic origin. Explanations for TuYV sequence differences between plants and the aphids present on respective plants and implications for the epidemiology and control of TuYV are discussed.

Genetic Differentiation and Migration Fluxes of Viruses from Melon Crops and Crop Edge Weeds.

Weeds surrounding crops may act as alternative hosts, playing important epidemiological roles as virus reservoirs and impacting virus evolution. We used high-throughput sequencing to identify viruses in Spanish melon crops and plants belonging to three pluriannual weed species, Ecballium elaterium, Malva sylvestris, and Solanum nigrum, sampled at the edges of the crops. Melon and E. elaterium, both belonging to the family Cucurbitaceae, shared three virus species, whereas there was no virus species overlap between melon and the other two weeds. The diversity of cucurbit aphid-borne yellows virus (CABYV) and tomato leaf curl New Delhi virus (ToLCNDV), both in melon and E. elaterium, was further studied by amplicon sequencing. Phylogenetic and population genetics analyses showed that the CABYV population was structured by the host, identifying three sites in the CABYV RNA-dependent RNA polymerase under positive selection, perhaps reflecting host adaptation. The ToLCNDV population was much less diverse than the CABYV one, likely as a consequence of the relatively recent introduction of ToLCNDV in Spain. In spite of its low diversity, we identified geographical but no host differentiation for ToLCNDV. Potential virus migration fluxes between E. elaterium and melon plants were also analyzed. For CABYV, no evidence of migration between the populations of the two hosts was found, whereas important fluxes were identified between geographically distant subpopulations for each host. For ToLCNDV, in contrast, evidence of migration from melon to E. elaterium was found, but not the other way around. IMPORTANCE It has been reported that about half of the emerging diseases affecting plants are caused by viruses. Alternative hosts often play critical roles in virus emergence as virus reservoirs, bridging host species that are otherwise unconnected and/or favoring virus diversification. In spite of this, the viromes of potential alternative hosts remain largely unexplored. In the case of crops, pluriannual weeds at the crop edges may play these roles. Here, we took advantage of the power of high-throughput sequencing to characterize the viromes of three weed species frequently found at the edges of melon crops. We identified three viruses shared by melon and the cucurbit weed, with two of them being epidemiologically relevant for melon crops. Further genetic analyses showed that these two viruses had contrasting patterns of diversification and migration, providing an interesting example on the role that weeds may play in the ecology and evolution of viruses affecting crops.

Identification of two putative novel deltapartitiviruses and an enamovirus in coriander transcriptomes.

Coriander is a herbaceous spice and condiment crop also known for its medicinal properties. The present study identified two putative novel deltapartitiviruses and an enamovirus tentatively named as Coriandrum sativum deltapartitivirus 1, 2 (CsDPV1, 2) and Coriandrum sativum enamovirus (CsEV) in the publicly available transcriptome-assembled contigs derived from coriander grown in India. CsDPV1 and 2 contained tripartite and bipartite genomes, respectively, with each genome segment encoding a single open reading frame (ORF). CsEV contained five ORFs encoding proteins P0, P1, P2, P3 and P5. Phylogenetic analysis revealed three distinct subgroups of deltapartitiviruses wherein CsDPV1 and 2 grouped in subgroup 3 and 1, respectively, whilst CsEV formed a distinct sub-clade within enamoviruses. Further, the presence of CsDPV2 in fruit samples of one of the cultivars from where the virus was identified was confirmed through RT-PCR assay and Sanger sequencing. The study highlights the need for further studies on understanding the importance and the biological properties of identified novel viruses.

Complete genome sequence of a novel polerovirus infecting Cynanchum rostellatum.

We detected a virus-like sequence in Cynanchum rostellatum leaves showing yellow mottle symptoms, found in Tokyo, Japan. RNA-Seq analysis revealed that the complete nucleotide sequence of the virus genome was 5,878 nucleotides in length and that it contained seven open reading frames (ORFs) specific to members of the genus Polerovirus. Accordingly, phylogenetic analysis revealed that the virus clustered with poleroviruses in the family Solemoviridae. The amino acid sequence identity values obtained by comparison of the deduced proteins of this virus and those of known members of the genus Polerovirus were lower than 90%, which is the species demarcation criterion of the taxon. The results indicate that this virus is a novel member of the genus Polerovirus, for which the name "cynanchum yellow mottle-associated virus" is proposed.

Complete genome sequence of a novel member of the genus Polerovirus from Cnidium officinale in South Korea.

The complete genome sequence of a novel virus found infecting Cnidium officinale, which we have named "cnidium polerovirus 1" (CnPV1), is 6,090 nucleotides in length, similar to those of other poleroviruses. Seven open reading frames (ORF0-5 and ORF3a) were predicted in this genome. CnPV1 shares 32.4%-38.9% full-length nucleotide sequence identity with other known polerovirus genome sequences. The putative P0, P1-2, P3-5, P3, and P4 proteins share 11.3%-19.5%, 37.1%-49.8%, 26.7%-39.5%, 40.8%-49.7%, and 40.8%-49.7% amino acid sequence identity, respectively, with homologous inferred protein sequences from known poleroviruses. Phylogenetic analysis of P1-2 and P3 sequences places CnPV1 with other members of the genus Polerovirus, indicating that it should be classified in a new distinct species.

Complete genome sequence of triticum yellow stripe virus, a new polerovirus infecting wheat (triticum aestivum) in China.

Wheat plants with yellow stripes on their leaves were collected in the city of Tai'an (Shandong province, China). High-throughput sequencing analysis of the collected plants showed that they were coinfected with wheat leaf yellowing-associated virus (WLYaV) and an unidentified polerovirus. The genome of the unidentified virus, tentatively named "triticum yellow stripe virus" (TriYSV), comprises 5,595 nucleotides and contains seven open reading frames (ORFs), with a typical polerovirus genome structure. Analysis by sequence alignment showed that TriYSV had the highest sequence similarity to wheat yellow dwarf virus (WYDV, a tentative member of the genus Polerovirus), with 87.3% nucleotide sequence identity over the whole genome. Except for P3a and the coat protein (CP), all of the proteins encoded by TriYSV showed < 90% amino acid identity to those of other poleroviruses. Phylogenetic analysis based on RNA-dependent RNA polymerase and CP amino acid sequences and complete genome nucleotide sequences showed that the poleroviruses WYDV, cereal yellow dwarf virus RPS (CYDV-RPS), CYDV-RPV, and barley yellow dwarf virus GPV are the most closely related to TriYSV. Thus, TriYSV is proposed to be a new member of the genus Polerovirus.

Complete genome sequence of Stellaria aquatica virus B, a novel polerovirus that infects Stellaria aquatica.

The complete genome sequence of Stellaria aquatica virus B (StAVB), a new member of the genus Polerovirus that infects Stellaria aquatica, was determined using high-throughput RNA sequencing with confirmation by Sanger sequencing. The complete StAVB genome (GenBank accession no. OP389993) is 5,900 nucleotide (nt) long with seven open reading frames (ORF0-5 and ORF3a) that encode putative proteins (P0-P5 and P3a) in a similar configuration to that of other typical poleroviruses. Pairwise sequence comparisons with other poleroviruses showed 38-50% nt sequence identity in the complete genome and 13-24%, 36-45%, 7-68%, and 6-50% amino acid sequence identity in (aa), for the P0, P1-2, P3, and P4 protein, respectively. These data, together with the results of phylogenetic analysis, indicate that StAVB should be classified as a new member of the genus Polerovirus, family Solemoviridae.

Turnip yellows virus variants differ in host range, transmissibility, and virulence.

Turnip yellows virus (TuYV; family Solemoviridae, genus Polerovirus, species Turnip yellows virus) is a genetically diverse virus that infects a broad range of plant species across the world. Due to its global economic significance, most attention has been given to the impact of TuYV on canola (syn. oilseed rape; Brassica napus). In Australia, a major canola-exporting country, TuYV isolates are highly diverse, with the most variation concentrated in open reading frame 5 (ORF 5), which encodes the readthrough domain (P5) component of the readthrough protein (P3P5), which plays an important role in host adaptation and aphid transmission. When analysing ORF 5, Australian TuYV isolates form three phylogenetic groups with just 45 to 49% amino acid sequence identity: variants P5-I, P5-II, and P5-III. Despite the possible implications for TuYV epidemiology and management, research examining phenotypic differences between TuYV variants is scarce. This study was designed to test the hypothesis that three TuYV isolates, representing each of the Australian P5 variants, differ phenotypically. In particular, the host range, vector species, transmissibility, and virulence of isolates 5414 (P5-I5414), 5509 (P5-II5509), and 5594 (P5-III5594) were examined in a series of glasshouse experiments. Only P5-I5414 readily infected faba bean (Vicia faba), only P5-II5509 infected chickpea (Cicer arietinum), and only P5-I5414 and P5-III5594 infected lettuce (Lactuca sativa). Myzus persicae transmitted each isolate, but Brevicoryne brassicae and Lipaphis pseudobrassicae did not. When using individual M. persicae to inoculate canola seedlings, P5-I5414 had significantly higher transmission rates (82%) than P5-II5509 (62%) and P5-III5594 (59%). As indicated by enzyme-linked immunosorbent assay absorbance values, P5-I5414 reached higher virus titers in canola than P5-II5509, which, in turn, reached higher titers than P5-III5594. P5-I5414 was also more virulent in canola than P5-II5509 and P5-III5594, inducing more severe foliar symptoms, stunting, and, in one of two experiments, seed yield loss. Results from this study compared to those of previous studies suggest that analysis of ORF 5 alone is insufficient to assign isolates to coherent strain categories, and further sequencing and phenotyping of field isolates is required.

Genomic characterization of two new viruses infecting Ageratum conyzoides in China.

Two new RNA viruses were identified in Ageratum conyzoides in China using high-throughput sequencing, and their genome sequences were determined using PCR and rapid amplification of cDNA ends. The new viruses, which have positive-sense, single-stranded RNA genomes, were provisionally named "ageratum virus 1" (AgV1) and "ageratum virus 2" (AgV2). AgV1 has a genome of 3,526 nucleotides with three open reading frames (ORFs) and shares 49.9% nucleotide sequence identity with the complete genome of Ethiopian tobacco bushy top virus (genus Umbravirus, family Tombusviridae). The genome of AgV2 consists of 5,523 nucleotides and contains five ORFs that are commonly observed in members of the genus Enamovirus of the family Solemoviridae. Proteins encoded by AgV2 exhibited the highest amino acid sequence similarity (31.7-75.0% identity) to the corresponding proteins of pepper enamovirus R1 (an unclassified enamovirus) and citrus vein enation virus (genus Enamovirus). Based on their genome organization, sequence, and phylogenetic relationships, AgV1 is proposed to be a new umbra-like virus of the family Tombusviridae, and AgV2 is proposed to be a new member of the genus Enamovirus of the family Solemoviridae.

Construction of an infectious full-length cDNA clone of a recombinant isolate of cucurbit aphid-borne yellows virus from Brazil.

In Brazil, the main viral disease of melon plant is severe yellowing disease called "Amarelão do Meloeiro," and a polerovirus, cucurbit aphid-borne yellows virus (CABYV) was considered one of the etiological agents. This virus is a recombinant strain originated from CABYV and unknown polerovirus. Due to unsuccessful mechanical inoculations of CABYV to host plants, the study of its biological characterization is hampered. Therefore, an infectious clone of the recombinant strain of CABYV was constructed using the Gibson Assembly technology. The full-length cDNA clones produced in this study showed to be infectious in three cucurbit species; melon (Cucumis melo), squash (a hybrid of Cucurbita maxima × C. moschata), and West Indian gherkin (Cucumis anguria) plants, but not in watermelon, cucumber, and zucchini plants. This insusceptibility of watermelon plants to the infectious clone corroborates the observation that this virus was never found in watermelon plants often located next to the infected melon plants. This infectious clone provides important tools for future study in developing resistant melon variety to CABYV infection.

Milder Autumns May Increase Risk for Infection of Crops with Turnip Yellows Virus.

Climate change has increased the risk for infection of crops with insect-transmitted viruses. Mild autumns provide prolonged active periods to insects, which may spread viruses to winter crops. In autumn 2018, green peach aphids (Myzus persicae) were found in suction traps in southern Sweden that presented infection risk for winter oilseed rape (OSR; Brassica napus) with turnip yellows virus (TuYV). A survey was carried out in spring 2019 with random leaf samples from 46 OSR fields in southern and central Sweden using DAS-ELISA, and TuYV was detected in all fields except one. In the counties of Skåne, Kalmar, and Östergötland, the average incidence of TuYV-infected plants was 75%, and the incidence reached 100% for nine fields. Sequence analyses of the coat protein gene revealed a close relationship between TuYV isolates from Sweden and other parts of the world. High-throughput sequencing for one of the OSR samples confirmed the presence of TuYV and revealed coinfection with TuYV-associated RNA. Molecular analyses of seven sugar beet (Beta vulgaris) plants with yellowing, collected in 2019, revealed that two of them were infected by TuYV, together with two other poleroviruses: beet mild yellowing virus and beet chlorosis virus. The presence of TuYV in sugar beet suggests a spillover from other hosts. Poleroviruses are prone to recombination, and mixed infection with three poleroviruses in the same plant poses a risk for the emergence of new polerovirus genotypes. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

An Aphid-Transmitted Virus Reduces the Host Plant Response to Its Vector to Promote Its Transmission.

The success of virus transmission by vectors relies on intricate trophic interactions between three partners, the host plant, the virus, and the vector. Despite numerous studies that showed the capacity of plant viruses to manipulate their host plant to their benefit, and potentially of their transmission, the molecular mechanisms sustaining this phenomenon has not yet been extensively analyzed at the molecular level. In this study, we focused on the deregulations induced in Arabidopsis thaliana by an aphid vector that were alleviated when the plants were infected with turnip yellows virus (TuYV), a polerovirus strictly transmitted by aphids in a circulative and nonpropagative mode. By setting up an experimental design mimicking the natural conditions of virus transmission, we analyzed the deregulations in plants infected with TuYV and infested with aphids by a dual transcriptomic and metabolomic approach. We observed that the virus infection alleviated most of the gene deregulations induced by the aphids in a noninfected plant at both time points analyzed (6 and 72 h) with a more pronounced effect at the later time point of infestation. The metabolic composition of the infected and infested plants was altered in a way that could be beneficial for the vector and the virus transmission. Importantly, these substantial modifications observed in infected and infested plants correlated with a higher TuYV transmission efficiency. This study revealed the capacity of TuYV to alter the plant nutritive content and the defense reaction against the aphid vector to promote the viral transmission.