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The size of viral genomes is limited, thus the majority of encoded proteins possess multiple functions. The main function of tobamoviral movement protein (MP) is to perform plasmodesmata gating and mediate intercellular transport of the viral RNA. MP is a remarkable example of a protein that, in addition to the initially discovered and most obvious function, carries out numerous activities that are important both for the manifestation of its key function and for successful and productive infection in general. Briefly, MP binds the viral genome, delivers it to the plasmodesmata (PD) and mediates its intercellular transfer. To implement the transport function, MP interacts with diverse cellular factors. Each of these cellular proteins has its own function, which could be different under normal conditions and upon viral infection. Here, we summarize the data available at present on the plethora of cellular factors that were identified as tobamoviral MP partners and analyze the role of these interactions in infection development. [ABSTRACT FROM AUTHOR]

Luteoviruses movement protein, P4, is a powerful virulence factor displaying dynamic subcellular localization, interacting partners, and complex functions during virus infection. The barley yellow dwarf virus (BYDV) P4 hijacks the plant's importin-mediated nuclear import pathway to target the nucleus, where it mediates G2 cell cycle arrest by regulating the Wee1–Cdc25–Cdk1 mitotic entry switch, ultimately causing plant dwarfism. The BYDV P4 manipulates cellular defense machinery such as the degradation of catalases, resulting in reactive oxygen species (ROS) bursts, leading to a hypersensitive response and cell death, which benefits the virus by enhancing BYDV proliferation, production of winged aphids, and virus transmission. RNA silencing is a potent defense mechanism against BYDV infection. Plants enhance this response by phosphorylating the BYDV P4, which redirects the protein to amplify antiviral RNA interference (RNAi), turning it from a foe to an ally. Viruses explore the potential multifunctional capacity of the proteins encoded in their compact genome to establish infection. P4 of luteoviruses has emerged as one such multifunctional protein. Expressed from an open reading frame (ORF) nested within coat protein ORF, it displays diverse subcellular localizations and interactions, reflecting its complex role in virus infection. In this review we explore how P4, constrained by overlapping ORFs, has evolved multiple functional motifs. We analyze these motifs' conservation across different barley yellow dwarf virus (BYDV) species and related poleroviruses. We also discuss how viral proteins cooperate to facilitate movement and localization of the virus throughout infection. We provide insights into potential future research directions and suggest strategies for developing potential antiviral-resistant approaches. [ABSTRACT FROM AUTHOR]

Summary: The development of plant virus‐based expression systems has expanded rapidly owing to their potential applications in gene functional and disease resistance research, and industrial production of pharmaceutical proteins. However, the low yield of certain proteins, especially high‐molecular‐mass proteins, restricts the production scale. In this study, we observed that the tobacco mosaic virus (TMV)‐mediated expression of a foreign protein was correlated with the amount of the movement protein (MP) and developed a TMV‐derived pAT‐transMP vector system incorporating trans‐complementation expression of MP. The system is capable of efficient expression of exogenous proteins, in particular those with a high molecular mass, and enables simultaneous expression of two target molecules. Furthermore, viral expression of competent CRISPR‐Cas9 protein and construction of CRISPR‐Cas9‐mediated gene‐editing system in a single pAT‐transMP construct was achieved. The results demonstrated a novel role for TMV‐MP in enhancing the accumulation of a foreign protein produced from the viral vector or a binary expression system. Further investigation of the mechanism underlying this role will be beneficial for optimization of plant viral vectors with broad applications. [ABSTRACT FROM AUTHOR]

This article reviews the literature concerning the largely forgotten tobamovirus gene products for which no functions have been ascribed. One of these gene products is the 54 kDa protein, representing the RNA-dependent RNA polymerase segment of the 183 kDa protein translated from the I1-subgenomic mRNA, but which has been found only by in vitro translation and not in plants. The other is a collection of small proteins, expressed from alternative reading frames (likely from internal ribosome entry sites) in either or both the movement protein gene or the capsid protein gene. Previously, two small proteins were referred to as the 4–6 kDa proteins, since only single proteins of such size had been characterized from tobacco mosaic virus and tomato mosaic virus genomes. Such putative proteins will be referred to here as P6 proteins, since many new proposed P6 open reading frames could be discerned, from an analysis of 45 of 47 tobamovirus genomes, with a coding capacity of >15 amino acids up to 94 amino acids, whereas other peptides with ≤15 amino acids were not considered here. The distribution of the putative P6 proteins among these tobamoviruses is described, as well as the various classes they fall into, based on their distribution with regard to the organization of other genes in the viral genomes. Models also are presented for possible functions of the 54 kDa protein and the P6 proteins, based on data in the literature. [ABSTRACT FROM AUTHOR]

This article, published in Frontiers in Plant Science, discusses the mechanisms of plant virus cell-to-cell transport. The authors focus on complementation studies involving viral movement proteins (MPs) and movement-deficient plant viruses. They provide examples of complementation studies with different plant viruses and discuss the potential mechanisms behind these complementations. The article emphasizes the importance of viral MPs in facilitating the transport of viral genomes through plasmodesmata, the channels connecting neighboring plant cells. The document also explores the ability of certain proteins to complement the transport of RNA viruses, specifically geminivirus C5 and P3 of the fungal virus. These proteins modify plasmodesmata, leading to actin remodeling and inhibition of callose deposition. The document also covers the specificity of transport through plasmodesmata and the mechanisms by which viral movement proteins provide selective intercellular transport. Additionally, the document provides a list of references for various scientific articles related to virology and plant viruses, which can be valuable for researchers studying plant viruses and their interactions with host plants. [Extracted from the article]

Movement proteins (MPs) encoded by plant viruses are essential for cell-to-cell transport of viral genomes through plasmodesmata. The genome of hibiscus green spot virus contains a module of two MP genes termed 'binary movement block' (BMB), encoding the proteins BMB1 and BMB2. Here, BMB1 is shown to induce a defense response in Nicotiana benthamiana plants that inhibits BMB-dependent virus transport. This response is characterized by the accumulation of reactive oxygen species, callose deposition in the cell wall, and upregulation of 9-LOX expression. However, the BMB1-induced response is inhibited by coexpression with BMB2. Furthermore, BMB1 is found to localize to subnuclear structures, in particular to Cajal bodies, in addition to the cytoplasm. As shown in experiments with a BMB1 mutant, the localization of BMB1 to nuclear substructures enhances BMB-dependent virus transport. Thus, the virus transport mediated by BMB proteins is modulated by (i) a BMB1-induced defense response that inhibits transport, (ii) suppression of the BMB1-induced response by BMB2, and (iii) the nuclear localization of BMB1 that promotes virus transport. Collectively, the data presented demonstrate multiple levels of interactions between viral pathogens and their plant hosts during virus cell-to-cell transport. [ABSTRACT FROM AUTHOR]

The tomato Tm-22 gene was considered to be one of the most durable resistance genes in agriculture, protecting against viruses of the Tobamovirus genus, such as tomato mosaic virus (ToMV) and tobacco mosaic virus (TMV). However, an emerging tobamovirus, tomato brown rugose fruit virus (ToBRFV), has overcome Tm-22 , damaging tomato production worldwide. Tm-22 encodes a nucleotide-binding leucine-rich repeat (NLR) class immune receptor that recognizes its effector, the tobamovirus movement protein (MP). Previously, we found that ToBRFV MP (MPToBRFV ) enabled the virus to overcome Tm-22 -mediated resistance. Yet, it was unknown how Tm-22 remained durable against other tobamoviruses, such as TMV and ToMV, for over 60 years. Here, we show that a conserved cysteine (C68) in the MP of TMV (MPTMV ) plays a dual role in Tm-22 activation and viral movement. Substitution of MPToBRFV amino acid H67 with the corresponding amino acid in MPTMV (C68) activated Tm-22 -mediated resistance. However, replacement of C68 in TMV and ToMV disabled the infectivity of both viruses. Phylogenetic and structural prediction analysis revealed that C68 is conserved among all Solanaceae-infecting tobamoviruses except ToBRFV and localizes to a predicted jelly-roll fold common to various MPs. Cell-to-cell and subcellular movement analysis showed that C68 is required for the movement of TMV by regulating the MP interaction with the endoplasmic reticulum and targeting it to plasmodesmata. The dual role of C68 in viral movement and Tm-22 immune activation could explain how TMV was unable to overcome this resistance for such a long period.

Rockmelon is a popular tropical fruit with high nutritional value. Cucumber mosaic virus (CMV), an aphid-transmitted virus, causes severe damage to rockmelon production. Exogenous application of double-stranded RNA (dsRNA) targeting viral sequences has shown promising results in controlling viral infection but has not been reported for CMV in rockmelon. In the current study, the protective effect of exogenous dsRNAs targeting the CMV coat protein (CP) and movement protein (MP) was tested in rockmelon. The effectiveness of dsRNA-mediated protection was measured by disease severity index (DSI) and compound enzyme-linked immunosorbent assay. The individual dsRNA CP and MP treatments each showed protection by reducing the DSI and virus titre, whilst a combination of dsRNA of CP and MP treatment showed much lower DSI (4.31-fold lower) and virus titre (4.91-fold lower) compared to CMV-inoculated plants without dsRNA treatment. Chlorophyll content, relative water content, plant height and number of leaves were not significantly different between virus challenged dsRNA-treated and mock-inoculated plants. Based on the DSI, two applications containing 9000 ng of dsRNA CP and MP in combination showed maximum CMV protection. Taken together, these results indicate that exogenous treatment containing a combination of dsRNA of CP and MP can control CMV infection in rockmelon. [ABSTRACT FROM AUTHOR]

The infection of host plants by many different viruses causes reactive oxygen species (ROS) accumulation and yellowing symptoms, but the mechanisms through which plant viruses counteract ROS-mediated immunity to facilitate infection and symptom development have not been fully elucidated. Most plant viruses are transmitted by insect vectors in the field, but the molecular mechanisms underlying virus‒host–insect interactions are unclear. In this study, we investigated the interactions among wheat, barley yellow dwarf virus (BYDV), and its aphid vector and found that the BYDV movement protein (MP) interacts with both wheat catalases (CATs) and the 26S proteasome ubiquitin receptor non-ATPase regulatory subunit 2 homolog (PSMD2) to facilitate the 26S proteasome-mediated degradation of CATs, promoting viral infection, disease symptom development, and aphid transmission. Overexpression of the BYDV MP gene in wheat enhanced the degradation of CATs, which leading to increased accumulation of ROS and thereby enhanced viral infection. Interestingly, transgenic wheat lines overexpressing BYDV MP showed significantly reduced proliferation of wingless aphids and an increased number of winged aphids. Consistent with this observation, silencing of CAT genes also enhanced viral accumulation and reduced the proliferation of wingless aphids but increased the occurrence of winged aphids. In contrast, transgenic wheat plants overexpressing TaCAT1 exhibited the opposite changes and showed increases in grain size and weight upon infection with BYDV. Biochemical assays demonstrated that BYDV MP interacts with PSMD2 and promotes 26S proteasome-mediated degradation of TaCAT1 likely in a ubiquitination-independent manner. Collectively, our study reveals a molecular mechanism by which a plant virus manipulates the ROS production system of host plants to facilitate viral infection and transmission, shedding new light on the sophisticated interactions among viruses, host plants, and insect vectors. This study investigated the interactions among wheat, barley yellow dwarf virus (BYDV), and its aphid vector and found that BYDV movement protein interacts with both wheat catalases (CATs) and the 26S proteasome ubiquitin receptor PSMD2 to facilitate 26S proteasome-mediated degradation of CATs. Thus, upon infection by BYDV, wheat plants exhibited increased levels of reactive oxygen species, leading to enhanced BYDV proliferation, disease symptom development, and aphid transmission. [ABSTRACT FROM AUTHOR]

The presence of viruses that spread to both plant and fungal populations in nature has posed intriguingly scientific question. We found a negative-strand RNA virus related to members of the family Phenuiviridae, named Valsa mali negative-strand RNA virus 1 (VmNSRV1), which induced strong hypovirulence and was prevalent in a population of the phytopathogenic fungus of apple Valsa canker (Valsa mali) infecting apple orchards in the Shaanxi Province of China. Intriguingly, VmNSRV1 encodes a protein with a viral cell-to-cell movement function in plant tissue. Mechanical leaf inoculation showed that VmNSRV1 could systemically infect plants. Moreover, VmNSRV1 was detected in 24 out of 139 apple trees tested in orchards in Shaanxi Province. Fungal inoculation experiments showed that VmNSRV1 could be bidirectionally transmitted between apple plants and V. mali, and VmNSRV1 infection in plants reduced the development of fungal lesions on leaves. Additionally, the nucleocapsid protein encoded by VmNSRV1 is associated with and rearranged lipid droplets in both fungal and plant cells. VmNSRV1 represents a virus that has adapted and spread to both plant and fungal hosts and shuttles between these two organisms in nature (phyto-mycovirus) and is potential to be utilized for the biocontrol method against plant fungal diseases. This finding presents further insights into the virus evolution and adaptation encompassing both plant and fungal hosts. [ABSTRACT FROM AUTHOR]

Plant viral movement proteins (MPs) serve a critical role in facilitating intercellular transport, pivotal for propagating infections from afflicted cells to their neighboring counterparts. Leveraging MPs within transient expression systems holds the potential to augment the expanse of protein expression zones. In this investigation, we present evidence showcasing the synergistic effects of fusing a transient expression system vector with the movement protein of tomato mosaic virus (ToMV MP), thus broadening the scope of protein expression within plant stem tissues. Through agroinfiltration, we achieved transient expression of green fluorescent protein (GFP) in tomato stem tissues, which was subsequently confirmed via immunoblotting with an anti-GFP antibody. Quantitative analysis unveiled that the co-expression of ToMV MP alongside GFP led to an over twofold increase in GFP production within stem tissues distal from the primary infection site. This research underscores the efficacy of combining ToMV MP with transient expression systems as a potent strategy for achieving transient expression of target genes within tomato plants. [ABSTRACT FROM AUTHOR]

Movement proteins (MPs) encoded by plant viruses are essential for cell-to-cell transport of viral genomes through plasmodesmata. The genome of hibiscus green spot virus contains a module of two MP genes termed ‘binary movement block’ (BMB), encoding the proteins BMB1 and BMB2. Here, BMB1 is shown to induce a defense response in Nicotiana benthamiana plants that inhibits BMB-dependent virus transport. This response is characterized by the accumulation of reactive oxygen species, callose deposition in the cell wall, and upregulation of 9-LOX expression. However, the BMB1-induced response is inhibited by coexpression with BMB2. Furthermore, BMB1 is found to localize to subnuclear structures, in particular to Cajal bodies, in addition to the cytoplasm. As shown in experiments with a BMB1 mutant, the localization of BMB1 to nuclear substructures enhances BMB-dependent virus transport. Thus, the virus transport mediated by BMB proteins is modulated by (i) a BMB1-induced defense response that inhibits transport, (ii) suppression of the BMB1-induced response by BMB2, and (iii) the nuclear localization of BMB1 that promotes virus transport. Collectively, the data presented demonstrate multiple levels of interactions between viral pathogens and their plant hosts during virus cell-to-cell transport.

Rice stripe disease caused by the rice stripe virus (RSV), which infects many Poaceae species in nature, is one of the most devastating plant viruses in rice that causes enormous losses in production. Ailanthone is one of the typical C20 quassinoids synthesized by the secondary metabolism of Ailanthus altissima, which has been proven to be a biologically active natural product with promising prospects and great potential for use as a lead structure for pesticide development. Based on the achievement of the systemic infection and replication of RSV in Nicotiana benthamiana plants and rice protoplasts, the antiviral properties of Ailanthone were investigated by determining its effects on viral-coding RNA gene expression using reverse transcription polymerase chain reaction, and Western blot analysis. Ailanthone exhibited a dose-dependent inhibitory effect on RSV NSvc3 expression in the assay in both virus-infected tobacco plants and rice protoplasts. Further efforts revealed a potent inhibitory effect of Ailanthone on the expression of seven RSV protein-encoding genes, among which NS3, NSvc3, NS4, and NSvc4 are the most affected genes. These facts promoted an extended and greater depth of understanding of the antiviral nature of Ailanthone against plant viruses, in addition to the limited knowledge of its anti-tobacco mosaic virus properties. Moreover, the leaf disc method introduced and developed in the study for the detection of the antiviral activity of Ailanthone facilitates an available and convenient screening method for anti-RSV natural products or synthetic chemicals. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt orthotospovirus (TSWV, Orthotospovirus tomatomaculae) resistance genes (Tsw, Sw5) have been identified in pepper and tomato plants. The development of resistant cultivars is one of the popular management strategies for overcoming viral infections. However, the breakdown of resistance genes has been documented from many places where resistant cultivars have been developed. This has mainly been due to the emergence of resistance-breaking (RB) lines because of the consecutive use of these cultivars. The development of these isolates may cause great losses in both tomato and pepper plants in Türkiye. To investigate the incidence of TSWV, 150 symptomatic samples were collected from widespread locations of tomato and pepper growing provinces in Türkiye. Samples were inoculated to enhance the virus titer and further confirmed by enzyme-linked immunosorbent assay (ELISA). The ELISA positive samples were confirmed by reverse transcription-polymerase chain reaction. The sequence-characterized amplified region (SCAR) and CAPS markers were used to screen resistance genes in tomato and pepper plants. Positive TSWV-isolates were partially sequenced to determine whether they had the previously reported mutations in NSs or NSm genes for RB isolates. As per the virus characterization, NSm and NSs amino acid sequences showed no previously identified mutations. Resistance gene-carrying isolates were amplified for partial genome sequences. Phylogenetic analyses revealed that both NSs and NSm were distributed in the same genetic pool. The N gene sequence comparison and phylogenetic analysis showed that the Turkish isolates were clustered in a separate clade. These findings provide insight into TSWV infections and resistance genes of pepper and tomato by phylogenetic analysis. [ABSTRACT FROM AUTHOR]

The genus Potyvirus is considered as the largest among plant single‐stranded (positive‐sense) RNA viruses, causing considerable economic damage to vegetable and fruit crops worldwide. Through the coordinated action of four viral proteins and a few identified host factors, potyviruses exploit the endomembrane system of infected cells for their replication and for their intra‐ and intercellular movement to and through plasmodesmata (PDs). Although a significant amount of data concerning potyvirus movement has been published, no synthetic review compiling and integrating all information relevant to our current understanding of potyvirus transport is available. In this review, we highlight the complexity of potyvirus movement pathways and present three potential nonexclusive mechanisms based on (1) the use of the host endomembrane system to produce membranous replication vesicles that are targeted to PDs and move from cell to cell, (2) the movement of extracellular viral vesicles in the apoplasm, and (3) the transport of virion particles or ribonucleoprotein complexes through PDs. We also present and discuss experimental data supporting these different models as well as the aspects that still remain mostly speculative. [ABSTRACT FROM AUTHOR]

Plant viruses employ Movement proteins (MP) for their cell to cell spread through plasmodesmata (PD). MP modifies the PD and increases its size exclusion limit (SEL). However, the mechanism by which MPs are targeted to the PD is still unresolved and there is a lack of consensus owing to limited studies on their biochemical and structural characters. The non structural protein m (NSm) functions as the MP in Orthotospoviruses. Tospoviral NSm associate with ER membrane. They also form tubules in protoplasts. Groundnut bud necrosis virus (GBNV), a tospovirus, infects several crop plants throughout India and is economically very important. GBNV NSm associates with the membrane strongly via the C-terminal coiled-coil domain, modifies the membrane and causes vesicle fusion in vitro and remodels the ER network into vesicles in vivo. These vesicles are in contrast to the tubules formed by other related tospovirus in cells lacking cell wall. In this review, five important questions on the cell-to-cell movement of tospoviruses have been addressed and based on the various reports, a plausible model on the cell-to-cell movement of Orthotospoviruses is presented.

Raspberry bushy dwarf virus (RBDV), recently renamed to Idaeovirus rubi, is one of the most common viruses infecting Rubus species worldwide but there is still a limited number of genome sequences available in the GenBank database and the majority of the sequences include partial sequences of RNA‐1 and RNA‐2. The distribution and incidence of RBDV in main raspberry and blackberry growing provinces in Turkey were monitored during 2015–2019 and 537 Rubus spp. samples were tested by both DAS‐ELISA and RT‐PCR. Among the tested samples, 36 samples tested positive for RBDV by DAS‐ELISA and 67 samples by RT‐PCR. There was relatively low nucleotide diversity among the Turkish isolates. Turkish isolates shared 93%–97.7%, 84.3%–98.9%, and 85%–99.2% nucleotide sequence identities with available sequences in the GenBank, in partial RNA‐1, movement protein (MP) and coat protein (CP) genes, respectively. In the phylogenetic tree constructed for RNA‐1, MP, and CP sequences, all Turkish raspberry isolates were clustered in a distinct clade. However, the blackberry isolates showed considerable variation in nucleotide sequences and were placed in three distinct groups. The divergent blackberry isolates showed high variability in MP (84.5%–89.3%) and CP (85.5%–89.7%) regions and were placed in a distinct group. The rest of blackberry isolates clustered together with sweet cherry RBDV isolates adjacent to the grapevine clade or together with raspberry isolates. The comparative analysis conducted on three RNA segments of RBDV highlighted the high sequence diversity of Turkish RBDV isolates. This study also emphasizes the importance of regular monitoring of RBDV infections in Turkey, with special regard to those Rubus spp. and grapevine accessions employed in conservation and selection programmes. In particular, the presence of new RBDV genetic variants and infection of Rubus species must be taken into account to choose a correct detection protocol and management strategy. [ABSTRACT FROM AUTHOR]

Abstract Tomato mottle mosaic virus (ToMMV) poses a threat to production and quality of tomato fruits. The Tm-2 2 gene confers resistance to some tobamoviruses by recognizing viral movement proteins. However, Tm-2 2 -mediated resistance against ToMMV is not well known. Here, we found that ToMMV could infect wild-type but not Tm-2 2 transgenic Nicotiana benthamiana plants and could also infect tomato cultivar Moneymaker but not resistant cultivar Jili with homozygous Tm-2 2 . Chimeric viral ToMMVToBRFV−MP with swapped ToMMV MP to MP of tomato brown rugose fruit virus could systemically infect Tm-2 2 transgenic N. benthamiana and tomato cultivars Jili plants. Further, transient expression of ToMMV MP in the leaves of Tm-2 2 transgenic N. benthamiana plants induced hypersensitive response-associated cell death, suggesting that the MP of ToMMV was the avirulent factor for the Tm-2 2 resistance gene. ToMMV could infect Tm-2 2 -containing cultivar Jinpeng 1 but not Chaobei. Sequence analysis revealed that cultivars Chaobei and Jinpeng 1 were heterozygous, where Chaobei consists of Tm-2 2 and Tm-2 genes, while Jinpeng 1 consists of Tm-2 2 and tm-2 genes. Transient co-expression assays showed that both Tm-2 2 and Tm-2 but not tm-2 could recognize ToMMV MP and induce hypersensitivity response-associated cell death in N. benthamiana leaves, suggesting that homozygous tomato harboring Tm-2 2 and heterozygous tomato containing Tm-2 2 and Tm-2 may exhibit more durable resistance to ToMMV than heterozygous tomato carrying Tm-2 2 and tm-2. Further, Tm-2 2 transgenic N. benthamiana and tomato cultivar Jili plants with silenced Tm-2 2 gene were susceptible to ToMMV. Also, silencing type-I J-domain MIP1 gene compromised Tm-2 2 -mediated resistance to ToMMV in Tm-2 2 transgenic N. benthamiana and tomato cultivar Jili. Moreover, we found that viral RNA could accumulate in the systemic leaves of Tm-2 2 transgenic N. benthamiana plants and tomato cultivar Jili at 35°C, but not at 20, 25, or 30°C. Altogether, our findings reveal that the Tm-2 2 confers resistance to ToMMV by recognizing MP, and the resistance is regulated by the allele combinations, accumulation levels of Tm-2 2 , MIP1, and the temperature.

The tomato Tm‐22 gene was considered to be one of the most durable resistance genes in agriculture, protecting against viruses of the Tobamovirus genus, such as tomato mosaic virus (ToMV) and tobacco mosaic virus (TMV). However, an emerging tobamovirus, tomato brown rugose fruit virus (ToBRFV), has overcome Tm‐22, damaging tomato production worldwide. Tm‐22 encodes a nucleotide‐binding leucine‐rich repeat (NLR) class immune receptor that recognizes its effector, the tobamovirus movement protein (MP). Previously, we found that ToBRFV MP (MPToBRFV) enabled the virus to overcome Tm‐22‐mediated resistance. Yet, it was unknown how Tm‐22 remained durable against other tobamoviruses, such as TMV and ToMV, for over 60 years. Here, we show that a conserved cysteine (C68) in the MP of TMV (MPTMV) plays a dual role in Tm‐22 activation and viral movement. Substitution of MPToBRFV amino acid H67 with the corresponding amino acid in MPTMV (C68) activated Tm‐22‐mediated resistance. However, replacement of C68 in TMV and ToMV disabled the infectivity of both viruses. Phylogenetic and structural prediction analysis revealed that C68 is conserved among all Solanaceae‐infecting tobamoviruses except ToBRFV and localizes to a predicted jelly‐roll fold common to various MPs. Cell‐to‐cell and subcellular movement analysis showed that C68 is required for the movement of TMV by regulating the MP interaction with the endoplasmic reticulum and targeting it to plasmodesmata. The dual role of C68 in viral movement and Tm‐22 immune activation could explain how TMV was unable to overcome this resistance for such a long period. [ABSTRACT FROM AUTHOR]

Begomoviruses, which belong to the Geminiviridae family, are intracellular parasites transmitted by whiteflies to dicotyledonous plants thatsignificantly damage agronomically relevant crops. These nucleus-replicating DNA viruses move intracellularly from the nucleus to the cytoplasm and then, like other plant viruses, cause disease by spreading systemically throughout the plant. The transport proteins of begomoviruses play a crucial role in recruiting host components for the movement of viral DNA within and between cells, while exhibiting functions that suppress the host's immune defense. Pioneering studies on species of the Begomovirus genus have identified specific viral transport proteins involved in intracellular transport, cell-to-cell movement, and systemic spread. Recent research has primarily focused on viral movement proteins and their interactions with the cellular host transport machinery, which has significantly expanded understanding on viral infection pathways. This review focuses on three components within this context: (i) the role of viral transport proteins, specifically movement proteins (MPs) and nuclear shuttle proteins (NSPs), (ii) their ability to recruit host factors for intra- and intercellular viral movement, and (iii) the suppression of antiviral immunity, with a particular emphasis on bipartite begomoviral movement proteins. [ABSTRACT FROM AUTHOR]

Introduction: Begomoviruses are mainly transmitted by whiteflies. However, a few begomoviruses can be transmitted mechanically. Mechanical transmissibility affects begomoviral distribution in the field. Materials and methods: In this study, two mechanically transmissible begomoviruses, tomato leaf curl New Delhi virus-oriental melon isolate (ToLCNDV-OM) and tomato yellow leaf curl Thailand virus (TYLCTHV), and two nonmechanically transmissible begomoviruses, ToLCNDV-cucumber isolate (ToLCNDV-CB) and tomato leaf curl Taiwan virus (ToLCTV), were used to study the effects of virus-virus interactions on mechanical transmissibility. Results: Nicotiana benthamiana and host plants were coinoculated through mechanical transmission with inoculants derived from plants that were mixinfected or inoculants derived from individually infected plants, and the inoculants were mixed immediately before inoculation. Our results showed that ToLCNDV-CB was mechanically transmitted with ToLCNDV-OM to N. benthamiana, cucumber, and oriental melon, whereas ToLCTV was mechanically transmitted with TYLCTHV to N. benthamiana and tomato. For crossing host range inoculation, ToLCNDV-CB was mechanically transmitted with TYLCTHV to N. benthamiana and its nonhost tomato, while ToLCTV with ToLCNDV-OM was transmitted to N. benthamiana and its nonhost oriental melon. For sequential inoculation, ToLCNDV-CB and ToLCTV were mechanically transmitted to N. benthamiana plants that were either preinfected with ToLCNDV-OM or TYLCTHV. The results of fluorescence resonance energy transfer analyses showed that the nuclear shuttle protein of ToLCNDV-CB (CBNSP) and the coat protein of ToLCTV (TWCP) localized alone to the nucleus. When coexpressed with movement proteins of ToLCNDV-OM or TYLCTHV, CBNSP and TWCP relocalized to both the nucleus and the cellular periphery and interacted with movement proteins. Discussion: Our findings indicated that virus-virus interactions in mixed infection circumstances could complement the mechanical transmissibility of nonmechanically transmissible begomoviruses and alter their host range. These findings provide new insight into complex virus-virus interactions and will help us to understand the begomoviral distribution and to reevaluate disease management strategies in the field. [ABSTRACT FROM AUTHOR]

Positive-stranded RNA virus movement proteins (MPs) generally lack sequence-specific nucleic acid-binding activities and display cross-family movement complementarity with related and unrelated viruses. Negative-stranded RNA plant rhabdoviruses encode MPs with limited structural and functional relatedness with other plant virus counterparts, but the precise mechanisms of intercellular transport are obscure. In this study, we first analyzed the abilities of MPs encoded by five distinct rhabdoviruses to support cell-to-cell movement of two positive-stranded RNA viruses by using trans-complementation assays. Each of the five rhabdovirus MPs complemented the movement of MP-defective mutants of tomato mosaic virus and potato X virus. In contrast, movement of recombinant MP deletion mutants of sonchus yellow net nucleorhabdovirus (SYNV) and tomato yellow mottle-associated cytorhabdovirus (TYMaV) was rescued only by their corresponding MPs, i.e., SYNV sc4 and TYMaV P3. Subcellular fractionation analyses revealed that SYNV sc4 and TYMaV P3 were peripherally associated with cell membranes. A split-ubiquitin membrane yeast two-hybrid assay demonstrated specific interactions of the membrane-associated rhabdovirus MPs only with their cognate nucleoproteins (N) and phosphoproteins (P). More importantly, SYNV sc4-N and sc4-P interactions directed a proportion of the N-P complexes from nuclear sites of replication to punctate loci at the cell periphery that partially colocalized with the plasmodesmata. Our data show that cell-to-cell movement of plant rhabdoviruses is highly specific and suggest that cognate MP-nucleocapsid core protein interactions are required for intra- and intercellular trafficking.IMPORTANCE Local transport of plant rhabdoviruses likely involves the passage of viral nucleocapsids through MP-gated plasmodesmata, but the molecular mechanisms are not fully understood. We have conducted complementation assays with MPs encoded by five distinct rhabdoviruses to assess their movement specificity. Each of the rhabdovirus MPs complemented the movement of MP-defective mutants of two positive-stranded RNA viruses that have different movement strategies. In marked contrast, cell-to-cell movement of two recombinant plant rhabdoviruses was highly specific in requiring their cognate MPs. We have shown that these rhabdovirus MPs are localized to the cell periphery and associate with cellular membranes, and that they interact only with their cognate nucleocapsid core proteins. These interactions are able to redirect viral nucleocapsid core proteins from their sites of replication to the cell periphery. Our study provides a model for the specific inter- and intracellular trafficking of plant rhabdoviruses that may be applicable to other negative-stranded RNA viruses.

Raspberry bushy dwarf virus (RBDV) is an economically significant pathogen of raspberry and grapevine, and it has also been found in cherry. Most of the currently available RBDV sequences are from European raspberry isolates. This study aimed to sequence genomic RNA2 of both cultivated and wild raspberry in Kazakhstan and compare them to investigate their genetic diversity and phylogenetic relationships, as well as to predict their protein structure. Phylogenetic and population diversity analyses were performed on all available RBDV RNA2, MP and CP sequences. Nine of the isolates investigated in this study formed a new, well-supported clade, while the wild isolates clustered with the European isolates. Predicted protein structure analysis revealed two regions that differed between α- and β-structures among the isolates. For the first time, the genetic composition of Kazakhstani raspberry viruses has been characterized. [ABSTRACT FROM AUTHOR]

Tomato mottle mosaic virus (ToMMV) poses a threat to production and quality of tomato fruits. The Tm-22 gene confers resistance to some tobamoviruses by recognizing viral movement proteins. However, Tm-22-mediated resistance against ToMMV is not well known. Here, we found that ToMMV could infect wild-type but not Tm-22 transgenic Nicotiana benthamiana plants and could also infect tomato cultivar Moneymaker but not resistant cultivar Jili with homozygous Tm-22. Chimeric viral ToMMVToBRFV−MP with swapped ToMMV MP to MP of tomato brown rugose fruit virus could systemically infect Tm-22 transgenic N. benthamiana and tomato cultivars Jili plants. Further, transient expression of ToMMV MP in the leaves of Tm-22 transgenic N. benthamiana plants induced hypersensitive response-associated cell death, suggesting that the MP of ToMMV was the avirulent factor for the Tm-22 resistance gene. ToMMV could infect Tm-22-containing cultivar Jinpeng 1 but not Chaobei. Sequence analysis revealed that cultivars Chaobei and Jinpeng 1 were heterozygous, where Chaobei consists of Tm-22 and Tm-2 genes, while Jinpeng 1 consists of Tm-22 and tm-2 genes. Transient co-expression assays showed that both Tm-22 and Tm-2 but not tm-2 could recognize ToMMV MP and induce hypersensitivity response-associated cell death in N. benthamiana leaves, suggesting that homozygous tomato harboring Tm-22 and heterozygous tomato containing Tm-22 and Tm-2 may exhibit more durable resistance to ToMMV than heterozygous tomato carrying Tm-22 and tm-2. Further, Tm-22 transgenic N. benthamiana and tomato cultivar Jili plants with silenced Tm-22 gene were susceptible to ToMMV. Also, silencing type-I J-domain MIP1 gene compromised Tm-22-mediated resistance to ToMMV in Tm-22 transgenic N. benthamiana and tomato cultivar Jili. Moreover, we found that viral RNA could accumulate in the systemic leaves of Tm-22 transgenic N. benthamiana plants and tomato cultivar Jili at 35°C, but not at 20, 25, or 30°C. Altogether, our findings reveal that the Tm-22 confers resistance to ToMMV by recognizing MP, and the resistance is regulated by the allele combinations, accumulation levels of Tm-22, MIP1, and the temperature. [ABSTRACT FROM AUTHOR]

The movement protein (MP) and coat protein (CP) of tobamoviruses play critical roles in viral cell‐to‐cell and long‐distance movement, respectively. Cucumber green mottle mosaic virus (CGMMV) is a member of the genus Tobamovirus. The functions of CGMMV MP and CP during viral infection remain largely unclear. Here, we show that CGMMV MP can interact with CP in vivo, and the amino acids at positions 79–128 in MP are vital for the MP–CP interaction. To confirm this finding, we mutated five conserved residues within the residue 79–128 region and six other conserved residues flanking this region, followed by in vivo interaction assays. The results showed that the conserved threonine residue at the position 107 in MP (MPT107) is important for the MP–CP interaction. Substitution of T107 with alanine (MPT107A) delayed CGMMV systemic infection in Nicotiana benthamiana plants, but increased CGMMV local accumulation. Substitutions of another 10 conserved residues, not responsible for the MP–CP interaction, with alanine inhibited or abolished CGMMV systemic infection, suggesting that these 10 conserved residues are possibly required for the MP movement function through a CP‐independent manner. Moreover, two movement function‐associated point mutants (MPF17A and MPD97A) failed to cause systemic infection in plants without impacting on the MP–CP interaction. Furthermore, we have found that co‐expression of CGMMV MP and CP increased CP accumulation independent of the interaction. MP and CP interaction inhibits the salicylic acid‐associated defence response at an early infection stage. Taken together, we propose that the suppression of host antiviral defence through the MP–CP interaction facilitates virus systemic infection. [ABSTRACT FROM AUTHOR]

Although the complete nucleotide sequence of strawberry vein banding virus (SVBV) has been determined and bioinformatic analysis has revealed that the SVBV genome could encode seven proteins, the precise function of each protein is unclear. This study provided evidence that the P1 protein of SVBV (SVBV-P1) possesses the following features. Bioinformatic and subcellular localization analyses showed that SVBV-P1 is localized in the cytoplasm and cell walls of epidermal cells in Nicotiana benthamiana, and it forms inclusion bodies associated with microtubules and the endoplasmic reticulum. Dilution experiments demonstrated that SVBV-P1 could move from the original agro-infiltrated cells to adjacent cells in N. benthamiana leaves. Further trans-complementation experiments demonstrated that SVBV-P1 could facilitate the intercellular movement of a movement-deficient potato virus X mutant in N. benthamiana leaves. Finally, yeast two-hybrid and bimolecular fluorescence complementation assays revealed that SVBV-P1 could interact with the SVBV coat protein, which is a major component of Caulimovirus virions. Results of the electrophoretic mobility shift assay indicated that SVBV-P1 lacks DNA-binding capability. In summary, the results suggest that SVBV-P1 is probably a movement protein of SVBV, providing new insights into the function of movement proteins of the Caulimovirus genus.

Plant-infecting viruses utilize various strategies involving multiple viral and host factors to achieve successful systemic infections of their compatible hosts. Lettuce infectious yellows virus (LIYV), genus Crinivirus, family Closteroviridae, has long, filamentous flexuous virions and causes phloem-limited infections in its plant hosts. The LIYV-encoded P26 is a distinct non-virion protein that shows no similarities to proteins in current databases: it induces plasmalemma deposits over plasmadesmata (PD) pit fields and is speculated to have roles in LIYV virion transport within infected plants. In this study, P26 was demonstrated to be a PD-localized protein, and its biological significance was tested in planta by mutagenesis analysis. An LIYV P26 knockout mutant (P26X) showed viral RNA replication and virion formation in inoculated leaves of Nicotiana benthamiana plants, but failed to give systemic infection. Confirmation by using a modified green fluorescent protein (GFP)-tagged LIYV P26X showed GFP accumulation only in infiltrated leaf tissues, while wild-type LIYV GFP readily spread systemically in the phloem. Attempts to rescue P26X by complementation in trans were negative. However a translocated LIYV P26 gene in the LIYV genome rescued systemic infection, but P26 orthologs from other criniviruses did not. Mutagenesis in planta assays showed that deletions in P26, as well as 2 of 11 specific alanine-scanning mutants, abolished the ability to systemically infect N. benthamianaIMPORTANCE Plant viruses encode specific proteins that facilitate their ability to establish multicellular/systemic infections in their host plants. Relatively little is known of the transport mechanisms for plant viruses whose infections are phloem limited, including those of the family Closteroviridae. These viruses have complex, long filamentous virions that spread through the phloem. Lettuce infectious yellows virus (LIYV) encodes a non-virion protein, P26, which forms plasmalemma deposits over plasmodesmata pit fields, and LIYV virions are consistently found attached to those deposits. Here we demonstrate that P26 is a unique movement protein required for LIYV systemic infection in plants. LIYV P26 shows no sequence similarities to other proteins, but other criniviruses encode P26 orthologs. However, these failed to complement movement of LIYV P26 mutants.

The necrogenic strain N5 of tomato mosaic virus (ToMV-N5) causes systemic necrosis in tomato cultivar Hezuo903. In this work, we mapped the viral determinant responsible for the induction of systemic necrosis. By exchanging viral genes between N5 and a non-necrogenic strain S1, we found that movement protein (MP) was the determinant for the differential symptoms caused by both strains. Compared with S1 MP, N5 MP had an additional ability to increase virus accumulation, which was not due to its functions in viral cell-to-cell movement. Actually, N5 MP, but not S1 MP, was a weak RNA silencing suppressor, which assisted viral accumulation. Sequence alignment showed that both MPs differed by only three amino acid residues. Experiments with viruses having mutated MPs indicated that the residue isoleucine at position 170 in MP was the key site for MP to increase virus accumulation, but also was required for MP to induce systemic necrosis in virus-infected tomato plants. Collectively, the lethal necrosis caused by N5 is dependent on its MP protein that enhances virus accumulation via its RNA silencing suppressor activity, probably leading to systemic necrosis responses in tomato plants. [ABSTRACT FROM AUTHOR]

Movement proteins (MPs) of plant viruses enable the translocation of viral genomes from infected to healthy cells through plasmodesmata (PD). The MPs functions involve the increase of the PD permeability and routing of viral genome both to the PD entrance and through the modified PD. Hibiscus green spot virus encodes two MPs, termed BMB1 and BMB2, which act in concert to accomplish virus cell-to-cell transport. BMB1, representing an NTPase/helicase domain-containing RNA-binding protein, localizes to the cytoplasm and the nucleoplasm. BMB2 is a small hydrophobic protein that interacts with the endoplasmic reticulum (ER) membranes and induces local constrictions of the ER tubules. In plant cells, BMB2 localizes to PD-associated membrane bodies (PAMBs) consisting of modified ER tubules and directs BMB1 to PAMBs. Here, we demonstrate that BMB1 and BMB2 interact in vitro and in vivo, and that their specific interaction is essential for BMB2-directed targeting of BMB1 to PAMBs. Using mutagenesis, we show that the interaction involves the C-terminal BMB1 region and the N-terminal region of BMB2. [ABSTRACT FROM AUTHOR]

ObjectiveAlfalfa mosaic virus (AMV) is one of the most important plant viruses that has a wide host range and economically is a destructive virus in the world and Iran. The aim of this research is to study the MP gene of Iranian AMV isolates and its application in the phylogenetical analysis and compare it with the CP gene. Materials and methodsDuring 2014 to 2017, a number of plant samples including alfalfa and weeds were collected from alfalfa fields in six Iranian provinces. ELISA test using polyclonal antibodies and RT-PCR were employed to check the AMV infection of the samples. Among the AMV infected samples, 20 isolates including 17 from alfalfa and three wild species including Sonchus oleraceus L., Chenopodium amaranticolor L. and Plantago ovate L. were chosen for phylogenetical analysis based on the sequence of the MP gene. ResultsPhylogenetic analysis based on the nucleotide sequence of movement protein (MP) gene of AMV including Iranian (n=20) and GenBank isolates (n=15) showed that all isolates are divided into two group I and II and each group is also divided into two subgroups A and B. The majority of Iranian isolates were placed in group II. All abroad and two Iranian isolates (Accession numbers: KX535454 and KX535456) were placed in subgroup IA, and subgroup IB is limited to three Iranian isolates (Accession numbers: KX535460, KX535458 and KX535462). Whereas based on the part of the nucleotide sequence of the MP gene (468nt), most of Iranian isolates, together with one Spanish isolate (JQ691163) were clustered in a new subgroup (IIB). ConclusionsAccording to the results of this study, it seems that the MP gene can be used to analyze the phylogenetic relationships between AMV isolates. Since the origin of AMV is from Far-East and central Asia and due to the host variability of the virus in these regions, AMV probably has a high genetic diversity in Iran.

Plant viruses exploit the endomembrane system of infected cells for their replication and cell-to-cell transport. The replication of viral RNA genomes occurs in the cytoplasm in association with reorganized endomembrane compartments induced by virus-encoded proteins and is coupled with the virus intercellular transport via plasmodesmata that connect neighboring cells in plant tissues. The transport of virus genomes to and through plasmodesmata requires virus-encoded movement proteins (MPs). Distantly related plant viruses encode different MP sets, or virus transport systems, which vary in the number of MPs and their properties, suggesting their functional differences. Here, we discuss two distinct virus transport pathways based on either the modification of the endoplasmic reticulum tubules or the formation of motile vesicles detached from the endoplasmic reticulum and targeted to endosomes. The viruses with the movement proteins encoded by the triple gene block exemplify the first, and the potyviral system is the example of the second type. These transport systems use unrelated mechanisms of endomembrane reorganization. We emphasize that the mode of virus interaction with cell endomembranes determines the mechanism of plant virus cell-to-cell transport. [ABSTRACT FROM AUTHOR]

Tomato brown rugose fruit virus is a new virus species in the Tobamovirus genus, causing substantial damage to tomato crops. Reports of recent tomato brown rugose fruit virus (ToBRFV) outbreaks from around the world indicate an emerging global epidemic. ToBRFV overcomes all tobamovirus resistances in tomato, including the durable Tm-22 resistance gene, which had been effective against multiple tobamoviruses. Here, we show that the ToBRFV movement protein (MPToBRFV) enables the virus to evade Tm-22 resistance. Transient expression of MPToBRFV failed to activate the Tm-22 resistance response. Replacement of the original MP sequence of tomato mosaic virus (ToMV) with MPToBRFV enabled this recombinant virus to infect Tm-22-resistant plants. Using hybrid protein analysis, we show that the elements required to evade Tm-22 are located between MPToBRFV amino acids 1 and 216 and not the C terminus, as previously assumed. Analysis of ToBRFV systemic infection in tomato revealed that ToBRFV spreads more slowly compared with ToMV. Interestingly, replacement of tobacco mosaic virus (TMV) and ToMV MPs with MPToBRFV caused an attenuation of systemic infection of both viruses. Cell-to-cell movement analysis showed that MPToBRFV moves less effectively compared with the TMV MP (MPTMV). These findings suggest that overcoming Tm-22 is associated with attenuated MP function. This may explain the high durability of Tm-22 resistance, which had remained unbroken for over 60 years.[Graphic: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Prunus necrotic ringspot virus (PNRSV) is an important pathogen of stone fruit species (Prunus sp.) including sweet (Prunus avium) and sour cherry (Prunus cerasus). In present study twenty seven cherry variants of PNRSV from three regions of Bulgaria were molecularly studied based on the nucleotide and amino acid sequences of the coat protein (CP) and the movement protein of RNA3 coding region. Fifteen more variants were studied only in the CP genome region. Phylogenetic analyses of the two genome regions revealed the formation of the four well-defined phylogroups PV32-I, PV96-II, PE5-III and CH30. Based on the nucleotide and amino acid sequences of CP genome region twenty-five and sixteen variants belonged to PV96-II and to PV32-I phylogroups, respectively. With one exclusion phylogenetic analyses based on the nucleotide and amino acid sequences of the MP genome region showed the same relationships among studied variants observed in the CP genome region. The comparison of CP and MP amino acid sequences revealed that the studied variants in each of the two groups, PV96-II and PV32-I had phylogroup-conserved amino acid residues. The results obtained showed a correlation between the phylogeny based on the nucleotide and amino acid sequences of RNA3 genomic region and the described for infected with PNRSV cherry trees pathotypes, known as rugose disease and mild mottle virosis. The specific amino acids present both in the CP and MP genome regions of all studied cherry PNRSV variants together with the symptoms on naturally infected cherry trees corresponded to the mild virosis pathotype. [ABSTRACT FROM AUTHOR]

Bunyaviruses cause diseases in vertebrates, arthropods, and plants. Here, we used high-throughput RNA-seq to identify a bunya-like virus in rice plants showing the dwarfing symptom, which was tentatively named rice dwarf-associated bunya-like virus (RDaBV). The RDaBV genome consists of L, M, and S segments. The L segment has 6562 nt, and encodes an RdRp with a conserved Bunya_RdRp super family domain. The M segment has 1667 nt and encodes a nonstructural protein (NS). The complementary strand of the 1120 nt S segment encodes a nucleocapsid protein (N), while its viral strand encodes a small nonstructural protein (NSs). The amino acid (aa) sequence identities of RdRp, NS, and N between RDaBV and viruses from the family Discoviridae were the highest. Surprisingly, the RDaBV NSs protein did not match any viral proteins. Phylogenetic analysis based on RdRp indicated that RDaBV is evolutionarily close to viruses in the family Discoviridae. The PVX-expressed system indicated that RDaBV N and NS may be symptom determinants of RDaBV. Our movement complementation and callose staining experiment results confirmed that RDaBV NSs is a viral movement protein in plants, while an agro-infiltration experiment found that RDaBV NS is an RNA silencing suppressor. Thus, we determined that RDaBV is a novel rice-infecting bunya-like virus. [ABSTRACT FROM AUTHOR]

Biological and molecular properties of six Prunus necrotic ringspot virus (PNRSV) isolates originating from sweet and sour cherry trees were studied. Double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) showed PNRSV infection in leaf samples from the respective source trees. While one of the infected source trees was symptomless, the other five showed symptoms, ranging from chlorotic to necrotic spots on the leaves. The reaction of greenhouse-grown seedlings of 22 herbaceous test plant species was investigated. The woody indicators Prunus serrulata cv. Kwanzan, wild cherry Prunus avium, P. cerasus, P. cerasifera and P. tomentosa were chip-budded. Chenopodium quinoa, Cucumis sativus cv. Amelia, C. sativus cv. Levina and P. tomentosa appeared as the most suitable test plants for the bioassay of the studied PNRSV isolates. The nucleotide sequences corresponding to the full-length coat (CP) and movement (MP) proteins were obtained. The nucleotide sequence identity among the studied isolates both in CP and MP genes was from 94% to 100%. The CP and MP amino acid sequence identities were from 95% to 100% and from 94% to 100%, respectively. Phylogenetic analyses performed with MP and CP nucleotide sequences showed that three isolates belonged to PV32-I and the other three to PV96-II phylogroups. Comparative amino acid analyses of MP and CP genes, together with the symptoms on naturally infected trees showed a higher affiliation of the studied isolates with the mild type than with the rugose types of isolates. The molecular variability correlated with the symptomatology on the naturally infected trees.

Begomoviruses belonging to the family Geminiviridae are plant‐infecting DNA viruses. Begomoviral movement protein (MP) has been reported to be required for virus movement, host range determination, and symptom development. In the present study, the FK506‐binding protein (FKBP)‐type peptidyl‐prolyl cis‐trans isomerase (NbFKPPIase) of Nicotiana benthamiana was identified by a yeast two‐hybrid screening system using the MP of tomato leaf curl New Delhi virus (ToLCNDV) oriental melon (OM) isolate (MPOM) as bait. Transient silencing of the gene encoding NbFKPPIase increased replication of three test begomoviruses, and transient overexpression decreased viral replication, indicating that NbFKPPIase plays a role in defence against begomoviruses. However, infection of N. benthamiana by ToLCNDV‐OM or overexpression of the gene encoding MPOM drastically reduced the expression of the gene encoding NbFKPPIase. Fluorescence resonance energy transfer analysis revealed that MPOM interacted with NbFKPPIase in the periphery of cells. Expression of the gene encoding NbFKPPIase was induced by salicylic acid but not by methyl jasmonate or ethylene. Moreover, the expression of the gene encoding NbFKPPIase was down‐regulated in response to 6‐benzylaminopurine and up‐regulated in response to gibberellin or indole‐3‐acetic acid, suggesting a role of NbFKPPIase in plant development. Transcriptome analysis and comparison of N. benthamiana transient silencing and overexpression of the gene encoding MPOM led to the identification of several differentially expressed genes whose functions are probably associated with cell cycle regulation. Our results indicate that begomoviruses could suppress NbFKPPIase‐mediated defence and biological functions by transcriptional inhibition and physical interaction between MP and NbFKPPIase to facilitate infection. [ABSTRACT FROM AUTHOR]

Biological and molecular properties of five Prune dwarf virus cherry isolates were studied. Double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) proved PDV infection in the respective source trees and absence of six other viruses infecting the cherry. Two of infected source trees were symptomless, and the other three trees showed deformed and elongated leaves with chlorotic lines and spots. The reaction of greenhouse-grown seedlings of 22 herbaceous test plant species was investigated. The woody indicators Prunus tomentosa and Prunus cerasifera were chip-budded. Cucumis sativus cv. Amelia, C. sativus cv. Levina, C. sativus cv. Tessa and Prunus tomentosa appeared as the most suitable test plants for bioassay of studied PDV isolates. The nucleotide sequences corresponding to the full-length coat protein (CP) of 657 bp were obtained. The identity among studied isolates in CP was 95.5–100% and 97.4–100% at nucleotide and amino acid levels, respectively. The movement protein (MP) sequences were 753 nucleotides long, translating 251 amino acids and shared 94.1–98.4% nucleotide and 96.8–99.2% amino acid identity. Constructed trees with the nucleotide sequences of both MP and CP genes of studied isolates and referent PDV cherry variants showed the formation of two phylogroups in the two genomic regions. All studied isolates separated into two clusters in group I. No correlation between the phylogenetic grouping and the biological properties, as well the geographical origin, was observed. [ABSTRACT FROM AUTHOR]

New evidences are emerging to support the importance of viral replication complexes (VRCs) in not only viral replication, but also viral cell-to-cell movement. Currently, how VRCs grow in size and colocalize with viral movement proteins (MPs) remains unclear. Herein, we performed live-cell imaging of red clover necrotic mosaic virus (RCNMV) dsRNA by using reporter B2-GFP plants. Tiny granules of dsRNA were formed along the endoplasmic reticulum (ER) at an early stage of infection. Importantly, the colocalization of the dsRNA granules with the virus-encoded p27 replication protein showed that these structures are components of VRCs. These granules moved throughout the cytoplasm, driven by the acto–myosin system, and coalesced with each other to form larger aggregates; the MPs were not associated with these processes. Notably, the MPs colocalized preferentially with large dsRNA aggregates, rather than with tiny dsRNA granules, suggesting that the increase in the size of VRCs promotes their colocalization with MPs. • Early dsRNA granules of RCNMV coalesced each other to form larger aggregates. • Acto-myosin system drives the intracellular movement of dsRNA granules. • Tiny dsRNA granules contain viral replicase, while associate less with MP. • Maturation of VRCs could be an important process for viral movement. [ABSTRACT FROM AUTHOR]

Abstract Cucurbit aphid-borne yellows virus (CABYV), melon aphid-borne yellows virus (MABYV) and suakwa aphid-borne yellows virus (SABYV) are three poleroviruses that infect cucurbit crops. Developing specific antisera against such viruses is crucial for their detection and functional understanding of related genes. However, no studies have yet reported viral detection using antisera against movement proteins (MP) in these three viruses. In this study, we generated plasmids expressing three viral MP genes, and transformed them into the Escherichia coli strain, Rosetta, to recombinantly express and purify fusion proteins. Then, polyclonal antisera were derived by immunizing New Zealand white rabbits, after which western blotting was used to determine the titer, sensitivity and specificity of the antisera. The antisera titers against MPCABYV, MPMABYV and MPSABYV were 1:512000, 1:256000 and 1:256000, respectively. The optimized working concentrations for the three antisera ranged between 1:10000 and 1:64000. Additionally, antisera against MPCABYV and MPMABYV only reacted with their corresponding MP proteins. Antiserum against MPSABYV not only had the strongest reaction with its MP, but also reacted weakly with MPCABYV and MPMABYV. All three antisera exerted no serological reactions with other poleroviruses. Furthermore, our data showed that all antisera specifically detected MPs in both Nicotiana benthamiana and cucumber leaves. Thus, we have established a system that sensitively detects three poleroviruses infecting cucurbits, using antisera against MPs. We provide a foundation for future research on the serological detection of these viruses, and interaction mechanisms between viruses and host plants.

Abstract Background Plant viruses move through plasmodesmata (PD) to infect new cells. To overcome the PD barrier, plant viruses have developed specific protein(s) to guide their genomic RNAs or DNAs to path through the PD. Results In the present study, we analyzed the function of Pepper vein yellows virus P4 protein. Our bioinformatic analysis using five commonly used algorithms showed that the P4 protein contains an transmembrane domain, encompassing the amino acid residue 117–138. The subcellular localization of P4 protein was found to target PD and form small punctates near walls. The P4 deletion mutant or the substitution mutant constructed by overlap PCR lost their function to produce punctates near the walls inside the fluorescent loci. The P4-YFP fusion was found to move from cell to cell in infiltrated leaves, and P4 could complement Cucumber mosaic virus movement protein deficiency mutant to move between cells. Conclusion Taking together, we consider that the P4 protein is a movement protein of Pepper vein yellows virus.

Ligularia jaluensis is an important medicinal and ornamental plant in China. However, the viruses capable of infecting Ligularia jaluensis remains unknown. Here, we identified a novel carlavirus, tentatively named ligularia jaluensis carlavirus (LJCV), as well as a known iris severe mosaic virus (ISMV), in L. jaluensis plants displaying chlorosis and yellow ring spot symptoms, using RNA-seq analysis. The LJCV genome consists of an 8497 ​nt positive-sense, single-stranded RNA [excluding the poly(A) tail], and contains six open reading frames (ORFs). Phylogenetic analyses based on the full-length genome and RNA-dependent RNA polymerase (RdRp) amino acid (aa) sequences revealed that LJCV clusters within an evolutionary branch alongside known viruses in the Carlavirus genus. The RdRp protein encoded by ORF1 of LJCV shared 45.38%-67.41% identity with the corresponding proteins of eight closely related carlaviruses. ORFs 2-4 constitute the triple gene block (TGB), with TGBp1 and TGBp3 localized in the endoplasmic reticulum (ER), while TGBp2 is localized at plasmodesmata (PD) and facilitates viral intercellular movement, as demonstrated by its ability to complement the potato virus X with movement-deficient mutant (PVX-Δp25-GFP). Additionally, ORF6 encodes a cysteine-rich protein (CRP) that is localized in the chloroplast and functions as a viral pathogenicity factor, inducing severe viral symptoms in the heterologous PVX expression system. Furthermore, we successfully constructed an infectious cDNA clone of LJCV, and found that it can infect Nicotiana benthamiana plants through mechanical inoculation or agrobacterium-mediated infiltration of the LJCV infectious clone. These findings enhance our understanding of the characteristics and host range of carlaviruses, as well as the viruses capable of infecting L. jaluensis., Competing Interests: Conflict of interest The authors declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript., (Copyright © 2024 The Authors. Publishing services by Elsevier B.V. All rights reserved.)

Objective Alfalfa mosaic virus (AMV) is one of the most important plant viruses that has a wide host range and economically is a destructive virus in the world and Iran. The aim of this research is to study the MP gene of Iranian AMV isolates and its application in the phylogenetical analysis and compare it with the CP gene. Materials and methods During 2014 to 2017, a number of plant samples including alfalfa and weeds were collected from alfalfa fields in six Iranian provinces. ELISA test using polyclonal antibodies and RT-PCR were employed to check the AMV infection of the samples. Among the AMV infected samples, 20 isolates including 17 from alfalfa and three wild species including Sonchus oleraceus L., Chenopodium amaranticolor L. and Plantago ovate L. were chosen for phylogenetical analysis based on the sequence of the MP gene. Results Phylogenetic analysis based on the nucleotide sequence of movement protein (MP) gene of AMV including Iranian (n=20) and GenBank isolates (n=15) showed that all isolates are divided into two group I and II and each group is also divided into two subgroups A and B. The majority of Iranian isolates were placed in group II. All abroad and two Iranian isolates (Accession numbers: KX535454 and KX535456) were placed in subgroup IA, and subgroup IB is limited to three Iranian isolates (Accession numbers: KX535460, KX535458 and KX535462). Whereas based on the part of the nucleotide sequence of the MP gene (468nt), most of Iranian isolates, together with one Spanish isolate (JQ691163) were clustered in a new subgroup (IIB). Conclusions According to the results of this study, it seems that the MP gene can be used to analyze the phylogenetic relationships between AMV isolates. Since the origin of AMV is from Far-East and central Asia and due to the host variability of the virus in these regions, AMV probably has a high genetic diversity in Iran. [ABSTRACT FROM AUTHOR]

Tomato cultivars containing the Tm‐22 resistance gene have been widely known to resist tobacco mosaic virus (TMV) and tomato mosaic virus. Tomato brown rugose fruit virus (ToBRFV), a new emerging tobamovirus, can infect tomato plants carrying the Tm‐22 gene. However, the virulence determinant of ToBRFV that overcomes the resistance conferred by the Tm‐22 gene remains unclear. In this study, we substituted the movement protein (MP) encoding sequences between ToBRFV and TMV infectious clones and conducted infectivity assays. The results showed that MP was the virulence determinant for ToBRFV to infect Tm‐22 transgenic Nicotiana benthamiana plants and Tm‐22‐carrying tomato plants. A TMV MP chimera with amino acid residues 60–186 of ToBRFV MP failed to induce hypersensitive cell death in the leaves of Tm‐22 transgenic N. benthamiana plants. Chimeric TMV containing residues 60–186 of ToBRFV MP could, but chimeric ToBRFV containing 61–187 residues of TMV MP failed to infect Tm‐22 transgenic N. benthamiana plants, indicating that 60–186 residues of MP were important for ToBRFV to overcome Tm‐22 gene‐mediated resistance. Further analysis showed that six amino acid residues, H67, N125, K129, A134, I147, and I168 of ToBRFV MP, were critical in overcoming Tm‐22‐mediated resistance in transgenic N. benthamiana plants and tomato plants. These results increase our understanding of the mechanism by which ToBRFV overcomes Tm‐22‐mediated resistance. [ABSTRACT FROM AUTHOR]

Background: Strawberry crinkle virus (SCV) is a member of the genus Cytorhabdovirus, family Rhabdovirida, and order Mononegavirales. SCV affects the production of various strawberry cultivars. In this study we investigated the genetic diversity of SCV in strawberry fields based on P3 (movement protein) gene. Methods and results: The samples were collected from strawberry fields in the Kurdistan Province, Iran. P3 gene from 20 SCV isolates, representing 18 nucleic acid haplotypes, is composed of 729 nucleotides, encoding a protein with 243 amino acids. SCV-P3 sequences shared 98.77%–99.86% nucleotide and 97.5%–100% amino acid sequence identity. Phylogenetic analyses of the new P3 sequences with two previously published SCV-P3 sequences from the Czech Republic showed that there are two major phylogroups (I and II) and three minor phylogroups in the body of the phylogeny, I-1, I-2, II-1. Comparisons of P3 gene sequences revealed a mutational bias, with more differences being transitions than transversions. The ratio of non-synonymous/synonymous nucleotide changes was < 1, indicating that SCV-P3 gene is under predominantly negative selection. Conclusions: Phylogenetic and sequence identity analyses showed that SCV isolates from Iran are closely related and have not diverged more than 2% based on P3 gene despite geographical separation and strawberry cultivar. This is the first report of the genetic diversity of SCV worldwide. [ABSTRACT FROM AUTHOR]

Genome of Banana bunchy top virus (BBTV) which causes the bunchy top disease in banana is transmitted by banana black aphid (Pentalonia nigronervosa). BBTV genome comprises six circular, single stranded DNA components, each coding for a single protein. Movement protein is encoded by the DNA-M component of BBTV, which plays a major role in the virus movement, causing systemic infection in banana. We report the isolation of BBTV and complete sequencing of DNA-M from 5 samples of Hill Banana and 2 samples of Grand Naine cultivated in Tamil Nadu by using the designed abutting primers in the conserved region. Bioinformatic analysis revealed two near identical BBTV DNA-M sequences among the five samples in Hill Banana. BBTV DNA-M isolated from both the samples of Grand Naine were identical. Multiple sequence alignment of the isolated movement protein with other sequences deposited in GenBank showed very high levels of sequence conservation. Further, phylogenetic analysis was done with DNA-M to determine evolutionary relationship with other isolates of BBTV available in India. Characterization of the movement protein of BBTV is very significant in the context of its role as a suppressor of gene silencing in banana.

Plant viruses exploit the endomembrane system of infected cells for their replication and cell-to-cell transport. The replication of viral RNA genomes occurs in the cytoplasm in association with reorganized endomembrane compartments induced by virus-encoded proteins and is coupled with the virus intercellular transport via plasmodesmata that connect neighboring cells in plant tissues. The transport of virus genomes to and through plasmodesmata requires virus-encoded movement proteins (MPs). Distantly related plant viruses encode different MP sets, or virus transport systems, which vary in the number of MPs and their properties, suggesting their functional differences. Here, we discuss two distinct virus transport pathways based on either the modification of the endoplasmic reticulum tubules or the formation of motile vesicles detached from the endoplasmic reticulum and targeted to endosomes. The viruses with the movement proteins encoded by the triple gene block exemplify the first, and the potyviral system is the example of the second type. These transport systems use unrelated mechanisms of endomembrane reorganization. We emphasize that the mode of virus interaction with cell endomembranes determines the mechanism of plant virus cell-to-cell transport.