Mutating the arginine residue within the FRNK motif of telosma mosaic virus (TelMV) HC-Pro protein attenuates viral infection and confers effective protection against TelMV in passion fruit (Passiflora edulis).

BACKGROUND: Telosma mosaic virus (TelMV, Potyvirus, Potyviridae) is an emerging viral pathogen that threatens passion fruit plantations worldwide. However, an efficient strategy for controlling such a virus is not yet available. Cross protection is a phenomenon in which pre-infection of a plant with one mild strain prevents or delays subsequent infection by the same or closely related virus. HC-Pro is the potyviral encoded multifunctional protein involved in several steps of viral infection, including multiplication, movement, transmission and RNA silencing suppression. In this study, we tested whether it is possible to generate attenuated viral strains capable of conferring protection against severe TelMV infection by manipulating the HC-Pro gene. RESULTS: By introducing point mutation into the conserved motif FRNK of HC-Pro that is essential for RNA silencing suppression, we have successfully obtained three attenuated mutants of TelMV (R181K, R181D, and R181E, respectively). These attenuated TelMV mutants could systemically infect passion fruit plants without noticeable symptoms. Pre-inoculation of one of these attenuated mutants confers efficient protection against subsequent infection by severe TelMV strain. Moreover, we demonstrated that the HC-Pros harbored by the attenuated mutants exhibit reduced RNA silencing suppression activity in Nicotiana benthamiana leaves. CONCLUSION: The attenuated TelMV mutants developed in this study that are suitable for cross protection offer a practical, powerful tool to fight against TelMV for sustainable passion fruit production. © 2024 Society of Chemical Industry.

Rubisco small subunit (RbCS) is co-opted by potyvirids as the scaffold protein in assembling a complex for viral intercellular movement.

Plant viruses must move through plasmodesmata (PD) to complete their life cycles. For viruses in the Potyviridae family (potyvirids), three viral factors (P3N-PIPO, CI, and CP) and few host proteins are known to participate in this event. Nevertheless, not all the proteins engaging in the cell-to-cell movement of potyvirids have been discovered. Here, we found that HCPro2 encoded by areca palm necrotic ring spot virus (ANRSV) assists viral intercellular movement, which could be functionally complemented by its counterpart HCPro from a potyvirus. Affinity purification and mass spectrometry identified several viral factors (including CI and CP) and host proteins that are physically associated with HCPro2. We demonstrated that HCPro2 interacts with both CI and CP in planta in forming PD-localized complexes during viral infection. Further, we screened HCPro2-associating host proteins, and identified a common host protein in Nicotiana benthamiana-Rubisco small subunit (NbRbCS) that mediates the interactions of HCPro2 with CI or CP, and CI with CP. Knockdown of NbRbCS impairs these interactions, and significantly attenuates the intercellular and systemic movement of ANRSV and three other potyvirids (turnip mosaic virus, pepper veinal mottle virus, and telosma mosaic virus). This study indicates that a nucleus-encoded chloroplast-targeted protein is hijacked by potyvirids as the scaffold protein to assemble a complex to facilitate viral movement across cells.

A Zinc Finger Motif in the P1 N Terminus, Highly Conserved in a Subset of Potyviruses, Is Associated with the Host Range and Fitness of Telosma Mosaic Virus.

P1 is the first protein translated from the genomes of most viruses in the family Potyviridae, and it contains a C-terminal serine-protease domain that cis-cleaves the junction between P1 and HCPro in most cases. Intriguingly, P1 is the most divergent among all mature viral factors, and its roles during viral infection are still far from understood. In this study, we found that telosma mosaic virus (TelMV, genus Potyvirus) in passion fruit, unlike TelMV isolates present in other hosts, has two stretches at the P1 N terminus, named N1 and N2, with N1 harboring a Zn finger motif. Further analysis revealed that at least 14 different potyviruses, mostly belonging to the bean common mosaic virus subgroup, encode a domain equivalent to N1. Using the newly developed TelMV infectious cDNA clones from passion fruit, we demonstrated that N1, but not N2, is crucial for viral infection in both Nicotiana benthamiana and passion fruit. The regulatory effects of N1 domain on P1 cis cleavage, as well as the accumulation and RNA silencing suppression (RSS) activity of its cognate HCPro, were comprehensively investigated. We found that N1 deletion decreases HCPro abundance at the posttranslational level, likely by impairing P1 cis cleavage, thus reducing HCPro-mediated RSS activity. Remarkably, disruption of the Zn finger motif in N1 did not impair P1 cis cleavage and HCPro accumulation but severely debilitated TelMV fitness. Therefore, our results suggest that the Zn finger motif in P1s plays a critical role in viral infection that is independent of P1 protease activity and self-release, as well as HCPro accumulation and silencing suppression. IMPORTANCE Viruses belonging to the family Potyviridae represent the largest group of plant-infecting RNA viruses, including a variety of agriculturally and economically important viral pathogens. Like all picorna-like viruses, potyvirids employ polyprotein processing as the gene expression strategy. P1, the first protein translated from most potyvirid genomes, is the most variable viral factor and has attracted great scientific interest. Here, we defined a Zn finger motif-encompassing domain (N1) at the N terminus of P1 among diverse potyviruses phylogenetically related to bean common mosaic virus. Using TelMV as a model virus, we demonstrated that the N1 domain is key for viral infection, as it is involved both in regulating the abundance of its cognate HCPro and in an as-yet-undefined key function unrelated to protease processing and RNA silencing suppression. These results advance our knowledge of the hypervariable potyvirid P1s and highlight the importance for infection of a previously unstudied Zn finger domain at the P1 N terminus.

The Single Distinct Leader Protease Encoded by Alpinia oxyphylla Mosaic Virus (Genus Macluravirus) Suppresses RNA Silencing Through Interfering with Double-Stranded RNA Synthesis.

The genomic 5'-terminal regions of viruses in the family Potyviridae (potyvirids) encode two types of leader proteases: serine-protease (P1) and cysteine-protease (HCPro), which differ greatly in the arrangement and sequence composition among inter-genus viruses. Most potyvirids have the same tandemly arranged P1 and HCPro, whereas viruses in the genus Macluravirus encode a single distinct leader protease, a truncated version of HCPro with yet-unknown functions. We investigated the RNA silencing suppression (RSS) activity and its underpinning mechanism of the distinct HCPro from alpinia oxyphylla mosaic macluravirus (aHCPro). Sequence analysis revealed that macluraviral HCPros have obvious truncations in the N-terminal and middle regions when aligned to their counterparts in potyviruses (well-characterized viral suppressors of RNA silencing). Nearly all defined elements essential for the RSS activity of potyviral counterparts are not distinguished in macluraviral HCPros. Here, we demonstrated that aHCPro exhibits a similar anti-silencing activity with the potyviral counterpart. However, aHCPro fails to block both the local and systemic spreading of RNA silencing. In line, aHCPro interferes with the dsRNA synthesis, an upstream step in the RNA silencing pathway. Affinity-purification and NanoLC-MS/MS analysis revealed that aHCPro has no association with core components or their potential interactors involving in dsRNA synthesis from the protein layer. Instead, the ectopic expression of aHCPro significantly reduces the transcript abundance of RDR2, RDR6, SGS3, and SDE5. This study represents the first report on the anti-silencing function of Macluravirus-encoded HCPro and the underlying molecular mechanism.

Internal electric field induced photocarriers separation of nickel-doped pyrite/pyrite homojunction with rich sulfur vacancies for superior Cr(VI) reduction.

Improving the separation efficiency and transfer ability of photoinduced electrons/holes in pyrite (FeS2)-based photocatalytic materials is significant for the photoreduction of hexavalent chromium (Cr(VI)) but still remains a challenge. Herein, a novel homojunction was prepared through in-situ growth of nickel (Ni) doped FeS2 nanoparticles on FeS2 nanobelts (denoted as Ni-FeS2/FeS2). Systematical characterizations revealed that Ni doped FeS2 nanoparticles have been successfully in situ grown along the lattice of FeS2 nanobelts. Photoreduction experiments demonstrated that the Ni-FeS2/FeS2 homojunction with 2 mmol Ni doping contents (denoted as 2Ni-FeS2/FeS2) exhibited the optimum Cr(VI) reduction efficiency among the studied catalysts. Density Functional Theory (DFT) calculated results verified that Ni doping could not only be advantageous for the formation of sulfur vacancies but also modify the band gap and band structure of FeS2 nanoparticles. Moreover, several doping energy levels caused by Ni doping have also appeared near the Fermi level of FeS2 nanoparticles. The migration paths of electrons and the existence of internal electric field (IEF) in homojunction were further verified by the calculation of work function. To sum up, the doping energy levels and IEF that produced by homojunction played important roles in accelerating the separation efficiency of its photogenerated carriers.

Biological and Molecular Characterization of Two Closely Related Arepaviruses and Their Antagonistic Interaction in Nicotiana benthamiana.

Previously, our group characterized two closely related viruses from Areca catechu, areca palm necrotic ringspot virus (ANRSV) and areca palm necrotic spindle-spot virus (ANSSV). These two viruses share a distinct genomic organization of leader proteases and represent the only two species of the newly established genus Arepavirus of the family Potyviridae. The biological features of the two viruses are largely unknown. In this study, we investigated the pathological properties, functional compatibility of viral elements, and interspecies interactions in the model plant, Nicotiana benthamiana. Using a newly obtained infectious clone of ANRSV, we showed that this virus induces more severe symptoms compared with ANSSV and that this is related to a rapid virus multiplication in planta. A series of hybrid viruses were constructed via the substitution of multiple elements in the ANRSV infectious clone with the counterparts of ANSSV. The replacement of either 5'-UTR-HCPro1-HCPro2 or CI effectively supported replication and systemic infection of ANRSV, whereas individual substitution of P3-7K, 9K-NIa, and NIb-CP-3'-UTR abolished viral infectivity. Finally, we demonstrated that ANRSV confers effective exclusion of ANSSV both in coinfection and super-infection assays. These results advance our understanding of fundamental aspects of these two distinct but closely related arepaviruses.

A cassava common mosaic virus vector for virus-induced gene silencing in cassava.

BACKGROUND: Cassava is an important crop for food security and industry in the least-developed and developing countries. The completion of the cassava genome sequence and identification of large numbers of candidate genes by next-generation sequencing provide extensive resources for cassava molecular breeding and increase the need for rapid and efficient gene function analysis systems in cassava. Several plant virus-induced gene silencing (VIGS) systems have been developed as reverse genetic tools for rapid gene function analysis in cassava. However, these VIGS vectors could cause severe viral symptoms or inefficient gene silencing. RESULTS: In this study, we constructed agroinfection-compatible infectious cDNA clones of cassava common mosaic virus isolate CM (CsCMV-CM, genus Potexvirus, family Alphaflexiviridae) that causes systemic infection with mild symptoms in cassava. CsCMV-CM was then modified to a viral vector carrying the Nimble cloning frame, which facilitates the rapid and high-throughput cloning of silencing fragments into the viral genome. The CsCMV-based vector successfully silenced phytoene desaturase (PDS) and magnesium chelatase subunit I (ChlI) in different cassava varieties and Nicotiana benthamiana. The silencing of the ChlI gene could persist for more than two months. CONCLUSIONS: This CsCMV-based VIGS system provides a new tool for rapid and efficient gene function studies in cassava.

A Newly Identified Virus in the Family Potyviridae Encodes Two Leader Cysteine Proteases in Tandem That Evolved Contrasting RNA Silencing Suppression Functions.

Potyviridae is the largest family of plant-infecting RNA viruses and includes many agriculturally and economically important viral pathogens. The viruses in the family, known as potyvirids, possess single-stranded, positive-sense RNA genomes with polyprotein processing as a gene expression strategy. The N-terminal regions of potyvirid polyproteins vary greatly in sequence. Previously, we identified a novel virus species within the family, Areca palm necrotic spindle-spot virus (ANSSV), which was predicted to encode two cysteine proteases, HCPro1 and HCPro2, in tandem at the N-terminal region. Here, we present evidence showing self-cleavage activity of these two proteins and define their cis-cleavage sites. We demonstrate that HCPro2 is a viral suppressor of RNA silencing (VSR), and both the variable N-terminal and conserved C-terminal (protease domain) moieties have antisilencing activity. Intriguingly, the N-terminal region of HCPro1 also has RNA silencing suppression activity, which is, however, suppressed by its C-terminal protease domain, leading to the functional divergence of HCPro1 and HCPro2 in RNA silencing suppression. Moreover, the deletion of HCPro1 or HCPro2 in a newly created infectious clone abolishes viral infection, and the deletion mutants cannot be rescued by addition of corresponding counterparts of a potyvirus. Altogether, these data suggest that the two closely related leader proteases of ANSSV have evolved differential and essential functions to concertedly maintain viral viability.IMPORTANCE The Potyviridae represent the largest group of known plant RNA viruses and account for more than half of the viral crop damage worldwide. The leader proteases of viruses within the family vary greatly in size and arrangement and play key roles during the infection. Here, we experimentally demonstrate the presence of a distinct pattern of leader proteases, HCPro1 and HCPro2 in tandem, in a newly identified member within the family. Moreover, HCPro1 and HCPro2, which are closely related and typically characterized with a short size, have evolved contrasting RNA silencing suppression activity and seem to function in a coordinated manner to maintain viral infectivity. Altogether, the new knowledge fills a missing piece in the evolutionary relationship history of potyvirids and improves our understanding of the diversification of potyvirid genomes.

The RNA-Dependent RNA Polymerase NIb of Potyviruses Plays Multifunctional, Contrasting Roles during Viral Infection.

Potyviruses represent the largest group of known plant RNA viruses and include many agriculturally important viruses, such as Plum pox virus, Soybean mosaic virus, Turnip mosaic virus, and Potato virus Y. Potyviruses adopt polyprotein processing as their genome expression strategy. Among the 11 known viral proteins, the nuclear inclusion protein b (NIb) is the RNA-dependent RNA polymerase responsible for viral genome replication. Beyond its principal role as an RNA replicase, NIb has been shown to play key roles in diverse virus-host interactions. NIb recruits several host proteins into the viral replication complexes (VRCs), which are essential for the formation of functional VRCs for virus multiplication, and interacts with the sumoylation pathway proteins to suppress NPR1-mediated immunity response. On the other hand, NIb serves as a target of selective autophagy as well as an elicitor of effector-triggered immunity, resulting in attenuated virus infection. These contrasting roles of NIb provide an excellent example of the complex co-evolutionary arms race between plant hosts and potyviruses. This review highlights the current knowledge about the multifunctional roles of NIb in potyvirus infection, and discusses future research directions.

Areca Palm Necrotic Ringspot Virus, Classified Within a Recently Proposed Genus Arepavirus of the Family Potyviridae, Is Associated With Necrotic Ringspot Disease in Areca Palm.

Areca palm (Areca catechu), one of the two most important commercial crops in Hainan, China, has been severely damaged by a variety of pathogens and insects. Here, we report a new disease, tentatively referred to as areca palm necrotic ringspot disease (ANRSD), which is highly epidemic in the main growing regions in Hainan. Transmission electron microscopy observation and small RNA deep sequencing revealed the existence of a viral agent of the family Potyviridae in a diseased areca palm plant (XC1). The virus was tentatively named areca palm necrotic ringspot virus (ANRSV). Subsequently, the positive-sense single-stranded genome of ANRSV isolate XC1 was completely determined. The genome annotation revealed the existence of two cysteine proteinases in tandem (HC-Pro1 and HC-Pro2) in the genomic 5' terminus of ANRSV. Sequence comparison and phylogenetic analysis suggested the taxonomic classification of ANRSV into the recently proposed genus Arepavirus in the family Potyviridae. Given the close relationship of ANRSV with another newly reported arepavirus (areca palm necrotic spindle-spot virus), the exact taxonomic status of ANRSV needs to be further investigated. In this study, a reverse transcription polymerase chain reaction assay for ANRSV-specific detection was developed and a close association between ANRSV and ANRSD was found.

Profile of siRNAs derived from green fluorescent protein (GFP)-tagged Papaya leaf distortion mosaic virus in infected papaya plants.

We used green fluorescent protein (GFP)-tagged Papaya leaf distortion mosaic virus (PLDMV-GFP) to track PLDMV infection by fluorescence. The virus-derived small interfering RNAs (vsiRNAs) of PLDMV-GFP were characterized from papaya plants by next-generation sequencing. The foreign GFP gene inserted into the PLDMV genome was also processed as a viral gene into siRNAs by components involved in RNA silencing. The siRNAs derived from PLDMV-GFP accumulated preferentially as 21- and 22-nucleotide (nt) lengths, and most of the 5'-terminal ends were biased towards uridine (U) and adenosine (A). The single-nucleotide resolution map revealed that vsiRNAs were heterogeneously distributed throughout the PLDMV-GFP genome, and vsiRNAs derived from the sense strand were more abundant than those from the antisense strand. The hotspots were mainly distributed in the P1 and GFP coding region of the antisense strand. In addition, 979 papaya genes targeted by the most abundant 1000 PLDMV-GFP vsiRNAs were predicted and annotated using GO and KEGG classification. Results suggest that vsiRNAs play key roles in PLDMV-papaya interactions. These data on the characterization of PLDMV-GFP vsiRNAs will help to provide insight into the function of vsiRNAs and their host target regulation patterns.

Analysis of the complete genomic sequence of a novel virus, areca palm necrotic spindle-spot virus, reveals the existence of a new genus in the family Potyviridae.

A novel virus, tentatively named "areca palm necrotic spindle-spot virus" (ANSSV), was identified in Areca catechu L. in Hainan, China, and its complete genomic sequence was determined. Its positive-sense single-stranded RNA genome is comprised of 9,437 nucleotides (nt), excluding the poly (A) tail, and contains one large open reading frame encoding a polyprotein of 3,019 amino acids (aa). A Blastp search showed that the polyprotein of ANSSV shared a maximum of 31%-32% aa sequence identity (with 86%-95% coverage) with all seven known macluraviruses. Nucleotide sequence comparison of the ORF of ANSSV to those of macluraviruses revealed identities ranging from 41.0% to 44.6%, which is less than the inter-genus identity values for the family Potyviridae. Phylogenetic analysis based on either the aa or nt sequence of the polyprotein did not cluster ANSSV into any established or unassigned genus of the family Potyviridae. Therefore, we suggest that ANSSV is the first member of a previously unrecognized genus of the family Potyviridae.

NbEXPA1, an α-expansin, is plasmodesmata-specific and a novel host factor for potyviral infection.

Plasmodesmata (PD), unique to the plant kingdom, are structurally complex microchannels that cross the cell wall to establish symplastic communication between neighbouring cells. Viral intercellular movement occurs through PD. To better understand the involvement of PD in viral infection, we conducted a quantitative proteomic study on the PD-enriched fraction from Nicotiana benthamiana leaves in response to infection by Turnip mosaic virus (TuMV). We report the identification of a total of 1070 PD protein candidates, of which 100 (≥2-fold increase) and 48 (≥2-fold reduction) are significantly differentially accumulated in the PD-enriched fraction, when compared with protein levels in the corresponding healthy control. Among the differentially accumulated PD protein candidates, we show that an α-expansin designated NbEXPA1, a cell wall loosening protein, is PD-specific. TuMV infection downregulates NbEXPA1 mRNA expression and protein accumulation. We further demonstrate that NbEXPA1 is recruited to the viral replication complex via the interaction with NIb, the only RNA-dependent RNA polymerase of TuMV. Silencing of NbEXPA1 inhibits plant growth and TuMV infection, whereas overexpression of NbEXPA1 promotes viral replication and intercellular movement. These data suggest that NbEXPA1 is a host factor for potyviral infection. This study not only generates a PD-proteome dataset that is useful in future studies to expound PD biology and PD-mediated virus-host interactions but also characterizes NbEXPA1 as the first PD-specific cell wall loosening protein and its essential role in potyviral infection.

Content determination of benzyl glucosinolate and anti-cancer activity of its hydrolysis product in Carica papaya L.

OBJECTIVE: To determine the content of benzyl glucosinolate (BG) in the pulp and the seed and investigate the anti-cancer activity of its hydrolysis product in Carica papaya L. METHODS: Determination of BG was performed on an Hypersil BDS C(18) column at the wavelength of 214 nm with 0.1% trifluoroacetic acid (TFA) aqueous solution (A) and 0.1%TFA acetonitrile (B) as the mobile phase. In vitro activity test was adopted with cultured human lung cancer H69 cell in vitro to investigate the inhibition rate of cell proliferation of benzyl isothiocyanate (BITC) against H69 cell. RESULTS: The pulp has more BG before the maturation of papaya and it nearly disappeared after papaya matured, while the seed contains BG at every stage. Activity test demonstrated that the a higher concentration of BITC would have better inhibition rate of cell proliferation on H69 cell, and the IC(50) was 6.5 µmol/L. CONCLUSIONS: BG also can be produced in the pulp of papaya and it will be stored in the seed after the fruit has been matured. The hydrolysis product of BG has certain cancer-prevention anti-cancer activities for human.

Helper component-proteinase (HC-Pro) protein of Papaya ringspot virus interacts with papaya calreticulin.

Potyviral helper component-proteinase (HC-Pro) is a multifunctional protein involved in plant-virus interactions. In this study, we constructed a Carica papaya L. plant cDNA library to investigate the host factors interacting with Papaya ringspot virus (PRSV) HC-Pro using a Sos recruitment two-hybrid system (SRS). We confirmed that the full-length papaya calreticulin, designated PaCRT (GenBank accession no. FJ913889), interacts specifically with PRSV HC-Pro in yeast, in vitro and in plant cells using SRS, in vitro protein-binding assay and bimolecular fluorescent complementation assay, respectively. SRS analysis of the interaction between three PaCRT deletion mutants and PRSV HC-Pro demonstrated that the C-domain (residues 307-422), with a high Ca(2+)-binding capacity, was responsible for binding to PRSV HC-Pro. In addition, quantitative real-time reverse transcriptase-polymerase chain reaction assay showed that the expression of PaCRT mRNA was significantly upregulated in the primary stage of PRSV infection, and decreased to near-basal expression levels in noninoculated (healthy) papaya plants with virus accumulation inside host cells. PaCRT is a new calcium-binding protein that interacts with potyviral HC-Pro. It is proposed that the upregulated expression of PaCRT mRNA may be an early defence-related response to PRSV infection in the host plant, and that interaction between PRSV HC-Pro and PaCRT may be involved in plant calcium signalling pathways which could interfere with virus infection or host defence.

[Analysis of the antigenicity of the expression product of fusion antigen epitope genes of FMDV].

AIM: From the different recombinants of FMDV antigen epitope, the highest antigenicity one was selected, and that provided research foundation for making researches on FMD plant-based vaccines which could effectively induce cell immune response and be characterized by high eurytopicity. METHODS: The single-chain DNA of 5 T-cell epitope genes and 2 B-cell epitope genes were synthesized. By gene splicing by overlap extension technique, 5 T-cell epitope genes were fused together into T and 2 B-cell epitope genes were fused together into B. With Ava III and Pst I which produced uniform stickiness terminal, T and B were fused into recombinats in which T and B existed in different position, namely 5'-T-B-T-3', 5'-T-T-B-3' and 5'-B-T-T-3'. With potato X virus expression vector (PVX) every antigen gene (T, B, T-B-T, T-T-B, B-T-T and VP1) was expected to be expressed in leaves of tobacco. RT-PCR analysis and conformed whether all of the antigen genes were transcribed. Indirect ELISA Western Dotblot conformed analysed the antigeni-city of these products. RESULTS: Every antigen genes were expressed successfully. The different products had different antigenicity, and 5'-T-B-T -3' was highest, 5'-B-T-T-3' was the second, and 5'-T-T-B-3' was lowest, but 5'-T-T-B-3' was higher than VP1, T or B. CONCLUSION: It is possible that gene engineering vaccine against FMDV with high eurytopicity and the induction of cell-immune response could be obtained by the different fusion ways with T and B cell epitopes existing in different position of recombinats, and that could have effect on immune activity of vaccines.

[Sequence analysis of the complete genome of papaya ringspot virus hainan isolate].

Total RNA was extracted from infected papaya (Carica papaya L.) leaves in Hainan Province, and the full-length sequences of papaya ringspot virus were amplified by RT-PCR and RACE, and its complete genomic sequence was assembled, named Hainan-P isolate. The RNA genome sequence of Hainan-P isolate was 10323 nucleotides (nts)in length,excluding the 3'-terminal poly(A) tail. And it was composed of a single open reading frame encoding a polyprotein of 3343 amino acids.. The result of homology analysis with twelve GenBank PRSV isolates showed that the polyprotein identity of Hainan-P ranged from 89. 8% to 93.2%, that was higher than the complete nt homology of 82.3% to 89.1%. The P1 amino acid was the least conserved (sharing homology only between 65.4% and 80.1%), whereas HC-Pro, CI and CP were the most conserved. Phylogenetic tree were constructed by the Neighbor-joining method in MEGA 3.1, which showed that PRSV isolates were obviously relevant to geographical origin, and it was impossible to delineate host-specific (P type and W type)evolution.

[Recent advances in plant virus vector systems].

Most plant viral genome is relatively small and easy for genetic manipulation and inoculation. Therefore, plant viral vectors are attractive tools for expression foreign genes in plants. This paper reviews two basic types of epitope presentation and polypeptide expression systems, and discusses the development and application prospect of plant virus vector.