Y.-H. Shi

A potyvirus p1 protein interacts with the Rieske Fe/S protein of its host

ABSTRACT Yeast two-hybrid (Y2H) screens were used to test for interactions between the P1 protein of Soybean mosaic virus Pinellia isolate (SMV-P) and a cDNA expression library of its host, the aroid Pinellia ternata. Of the 13 independent interacting clones identified, ten were identical and had an open reading frame predicted to encode a 23.7-kDa protein closely related to the cytochrome b6/f complex Rieske Fe/S genes of plants. The interaction between SMV-P-P1 and the mature Rieske Fe/S protein (without transit peptide) of the host was confirmed by in vitro co-immunoprecipitation of the two proteins. Y2H assays using different parts of the two proteins showed that only the N-terminal part (amino acids 1-82) of SMV-P P1 was responsible for the interaction with the Rieske Fe/S protein and that amino acids 1-33 interacted only with the transit peptide, while amino acids 34-82 could interact with the entire Rieske Fe/S protein. SMV-P P1 also interacted moderately with the Rieske Fe/S protein of its other hosts, soybean and Zantedeschia aethiopica, but weakly with that of the non-host Arabidopsis thaliana. The P1-Rieske Fe/S protein interactions are likely to be involved in symptom development, and the very variable N-terminus of P1 may play an important role in host adaptation.

Protein-protein interactions in two potyviruses using the yeast two-hybrid system.

Interactions between all ten mature proteins of the potyviruses Soybean mosaic virus (Pinellia ternata isolate) and Shallot yellow stripe virus were investigated using yeast two-hybrid (Y2H) assays. Consistently strong self-interactions were found between the pairs of HC-Pro, VPg, NIa-Pro, NIb and CP in both viruses. Apart from the NIb, such interactions have been previously reported for some other potyviruses. The 6K1/NIa-Pro combination gave a consistently moderate to strong interaction in both directions for both viruses. This interaction occurred even when the 6K1 of SMV-P was truncated to eliminate the C-terminal motif that acts as a recognition site for cleavage by the NIa-Pro. Many other interactions occurred only in one direction or only for one of the two viruses. When taken together with other published reports, the data suggest that interactions detected by Y2H should be regarded as only preliminary indications.

Further molecular characterisation of potyviruses infecting aroid plants for medicinal use in China

Summary.Degenerate primers were used to detect and amplify 3′-terminal genome fragments of potyviruses from medicinal aroid plants growing at 16 sites in China. Virus was detected in 7 samples of which six, all of Pinellia ternata, contained a strain of soybean mosaic virus (SMV) similar to that previously reported from this host in China. The complete sequence of one isolate and the P1 protein coding region of the other isolates were also sequenced. In all cases, the P1 proteins resembled isolates of Dasheen mosaic virus (DsMV) more closely than SMV, confirming earlier suggestions of recombination in this region. In a phylogenetic analysis of SMV, DsMV and related sequences, the aroid sequences of SMV formed a distinct group which also included a sequence published as Zantedeschia symptomless virus (AF469171). One of the P. ternata samples was also infected with a second potyvirus, the 3′-terminal sequence of which was similar to DsMV and to some sequences published as Vanilla mosaic virus. The seventh infected sample was Typhonium flagelliforme and the virus from it was identified from its sequence as zantedeschia mosaic virus (ZaMV), providing the first report of this virus from mainland China.

The ‘6K1’ protein of a strain of Soybean mosaic virus localizes to the cell periphery

SummaryThe ‘6K1’ protein of the Pinellia isolate of Soybean mosaic virus was cloned into a prokaryotic expression vector and a polyclonal antiserum raised to the expressed fusion protein. In immunogold labeling of thin sections of infected leaves of Pinellia ternata, specific labeling occurred at the cell periphery. This might suggest that the potyvirus ‘6K1’ protein plays some role in viral cell-to-cell movement but the lack of transmembrane domains suggests that it does not conform to currently-recognized patterns of viral movement proteins.

The complete sequence of the genomic RNA of an isolate of Lily virus X (genus Potexvirus )

Summary.The complete sequence of the genomic RNA of an isolate of Lily virus X (LVX) has been determined for the first time. The isolate from the Netherlands was 5823 nucleotide (nt) long excluding the 3′-poly(A) tail, making it the shortest reported potexvirus sequence. The 5′-non-coding region begins with GGAAAA like that of Scallion virus X (ScaVX) and some isolates of Cymbidium mosaic virus (CymMV), whereas those of other sequenced potexviruses probably all begin with GAAAA. The genome organisation was similar to that of other members of the genus except that a TGBp3-like region lacked a normal AUG start codon. A phylogenetic analysis based on the entire coding sequence showed that LVX was most closely related to Strawberry mild yellow edge virus and belonged in a subgroup of the genus that also contains CymMV, Narcissus mosaic virus, ScaVX, Pepino mosaic virus, Potato aucuba mosaic virus and White clover mosaic virus.

A new potyvirus from Thunberg fritillary (Fritillaria thunbergii Miq.) in Zhejiang, China

Summary.A potyvirus causing mosaic symptoms in Thunberg fritillary (Fritillaria thunbergii) was found at two sites in Zhejiang province, China. The virus was readily mechanically transmitted to its original host but not to any of 17 other widely used plant virus indicators. A polyclonal antiserum raised to purified virus particles reacted with its homologous virus but not with a range of other viruses (including 16 potyvirus species). In electron microscopy, virus particles and inclusion bodies typical of a potyvirus were seen. The complete nucleotide sequence of an isolate from Ningbo was determined. It was 9723 nt long and sequence analyses predicted the standard potyvirus organisation. The partial sequence (1664 nts at the 3′-terminus) of an isolate from Panan was also determined; the two sequences had 96.9% nt identity. In sequence comparisons and phylogenetic analyses with completely sequenced potyviruses, the new virus was most closely related to Lily mottle virus (53.0% aa identity) and Leek yellow stripe virus. The most closely related incomplete sequence in the international databases was for Lycoris mild mottle virus (72.8% nt identity in their coat proteins). These results suggest that the virus studied is a new species in the genus Potyvirus, which we have tentatively named Thunberg fritillary mosaic virus.

Detection and characterisation of a second potyvirus from Thunberg fritillary in China

Summary.Plants of Thunberg fritillary (Fritillaria thunbergii Miq.) from Zhejiang Province, were found to be co-infected with two distinct potyviruses. One was an isolate of the recently reported Thunberg fritillary mosaic virus (TFMV; Wei et al., (2005) Arch Virol 150: 1271–1280), while the other was a distinct virus that did not react with TFMV antiserum nor with antisera to 17 other potyviruses, except for a weak reaction with antibodies produced to soybean mosaic virus (SMV) Pinellia strain. Both viruses could be transmitted mechanically to their original host but not to any of a range of commonly used indicator plants. No local lesion host was identified that would enable the viruses to be propagated independently. The complete sequences of both viruses were determined; that of the new virus (9656 nt) had the typical genome organisation and recognised sequence motifs of a potyvirus, encoding a putative polyprotein of 351 kDa. Phylogenetic analysis, sequence comparisons, and the pattern of polyprotein cleavage sites all indicated that it was a member of the Bean common mosaic virus subgroup. The most closely related species are Soybean mosaic virus and Wisteria vein mosaic virus, with 68–69% amino acid identity between their polyproteins. This is sufficiently different for the new virus to be regarded as a distinct species, which we have tentatively named Fritillary virus Y.

Complete nucleotide sequence of the genomic RNA of Narcissus yellow stripe virus from Chinese narcissus in Zhangzhou city, China

Plants of the genus Narcissus are known to be susceptible to a complex mixture of filamentous viruses. These include at least four members of the genus Potyvirus, namely Narcissus yellow stripe virus (NYSV), Narcissus late season yellows virus (NLSYV), Narcissus degeneration virus (NDV)(only in N. tazetta) and Ornithogalum mosaic virus (OrMV). Chinese narcissus (Narcissus tazetta var. chinensis) is an economically important ornamental plant in China, and virus disease causes loss of yield and poor quality. Recently, degenerate primers were

Narcissus symptomless virus: a new carlavirus of daffodils

Summary.A filamentous virus, with particles 600–650 nm long, was purified from Narcissus pseudonarcissus (daffodil) in Hangzhou and an antiserum prepared. After mechanical inoculation, the virus could be detected serologically in Narcissus species but not in some commonly used virus indicators. Infection was symptomless. The complete sequence of the genomic RNA (8281 nt) showed six predicted ORFs typical of carlaviruses. Pairwise comparisons of gene sequences and phylogenetic analysis demonstrated that the new virus should be classified as a carlavirus but that it was not closely related to members of any current species. We propose the name Narcissus symptomless virus (NSV).

Characterisation of the welsh onion isolate of Shallot yellow stripe virus from China

Summary.The host range and nucleotide sequence of shallot yellow stripe virus (SYSV) from welsh onion in Shandong province, China is described. Of the plants tested, only shallot and welsh onion became infected but most shallot plants were symptomless. The complete sequence of one isolate (10429 nt) and the 3′-terminal 3540 nts of a second isolate were determined. They had c. 90% nt identity to one another and to published (partial) sequences of SYSV. SYSV was most closely related to onion yellow dwarf virus (OYDV) and resembled it in having a much larger P3 protein than other species in the genus.