Camille Kerlan

Genomic variability in Potato potyvirus Y (PVY): evidence that PVYNW and PVYNTN variants are single to multiple recombinants between PVYO and PVYN isolates

Summary. Fourteen Potato virus Y (PVY) isolates representative of PVYO, PVYN, PVYNTN and PVYNW groups were characterised at genomic level. Restriction fragment length polymorphism study (RFLP) of each gene of these isolates and sequencing of the first 2700 nucleotides of two PVYNW isolates were performed. A mosaic structure was revealed in PVYNW and PVYNTN genomes, which showed either PVYO or PVYN-like sequences, depending on the particular gene. Indeed, starting from the 5′-end, these isolates showed a switching, from PVYN- to PVYO-like sequence, in the HC-Pro C-terminal region. Reversion to PVYN-like sequence was also revealed in the NIa N-terminal area of PVYNTN isolates, followed by a switching back to a PVYO-like sequence in the CP gene. Lastly, some PVYNW isolates showed a switching from PVYO- to PVYN-like sequence in the P1 N-terminal part, thus separating our PVYNW isolates into two subgroups. All these apparent recombination events were shown by statistical analysis. Comparison of molecular traits with pathogenic properties of our isolates suggested that the HC-Pro protein is involved in induction of necrosis in tobacco leaves, and the NIa, NIb and/or CP protein in necrosis in potato tubers. Nevertheless, multiple recombination events observed in the PVYNTN genome may play a role in the latter phenomenon.

Discussion paper: The naming of Potato virus Y strains infecting potato.

SummaryPotato virus Y (PVY) strain groups are based on host response and resistance gene interactions. The strain groups PVYO, PVYC and PVYN are well established for the isolates infecting potato in the field. A switch in the emphasis from host response to nucleotide sequence differences in the virus genomes, detection of isolates recombining sequences of different strains, and the need to recognize isolates that cause necrotic symptoms in potato tubers have led to the assignment of new acronyms, especially to isolates of the PVYN strain group. This discussion paper proposes that any newly found isolates should be described within the context of the original strain groups based on the original methods of distinguishing strains (i.e., tobacco and potato assays involving use of ‘differential’ potato cultivars). Additionally, sequence characterization of the complete genomes of isolates is highly recommended. However, it is acceptable to amend the names of PVY isolates with additional, specific codes to show that the isolate differs at the molecular, serological or phenotypic level from the typical strains within a strain group. The new isolates should preferably not be named using geographical, cultivar, or place-association designations. Since many new variants of PVY are being discovered, any new static classification system will be meaningless for the time being. A more systematic investigation and characterization of PVY from potato at the biological and molecular levels should eventually result in a biologically meaningful genetic strain concept.

Characterization of potato potyvirus Y (PVY) isolates from seed potato batches. Situation of the NTN, Wilga and Z isolates

AbstractA collection of 38 PVY isolates from seed potato batches, originating from several Western European countries, was characterized by using current biological, serological and molecular tools differentiating PVY strains and groups. The correlation between the three kinds of tests was good but not absolute. No single serological or PCR method was able to discriminate among the five isolate groups found. Twenty-nine isolates belonged to the PVYN strain and six to the PVYO strain. No PVYC was found. Two other isolates reacted serologically like PVYO, but were unable to elicit a hypersensitive response from the Nytbr gene and probably represent the PVYZ group. At the molecular level, these two isolates showed a combination of both PVYO and PVYN and could be recombinants of these strains. Another isolate reacted serologically like PVYO, but induced vein necrosis in tobacco, like PVYN-Wilga. Some PVYN isolates caused tuber ring necrosis in glasshouse conditions. These might belong to the PVYNTN group. The PVYNTN, PVYN-Wilga and PVYZ groups probably represent pathotypes within strains PVYN and PVYO, respectively. The present study also confirms previous reports showing a high genetic variation at the 5

The intestine is a site of passage for potato leafroll virus from the gut lumen into the haemocoel in the aphid vector,Myzus persicae Sulz

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The Helper Component Proteinase Cistron of Potato virus Y Induces Hypersensitivity and Resistance in Potato Genotypes Carrying Dominant Resistance Genes on Chromosome IV

end within the PVYN strain.

Ultrastructural study of acquisition and retention of potato leafroll luteovirus in the alimentary canal of its aphid vector,Myzus persicae Sulz

Based on the sequence polymorphism in the 5′ terminal part of the viral genome, a range of PVYN isolates were characterized by polymerase chain reaction (PCR) followed by restriction fragment length polymorphism (RFLP). Three pairs of primers selected in the 5′ non-translated and P1 protein region were tested. Two of them yielded PCR products of about 1Kb from all isolates tested. Restriction analysis of the PCR products gave two distinct electrophoretic patterns, whichever of the three enzymes was used. In this way, the 18 isolates were separated into two easily identifiable subgroups. All tuber necrosing isolates (PVYNTN) were clustered in the same subgroup.

Transformation of cauliflower (Brassica oleracea var. botrytis) by transfer of cauliflower mosaic virus genes through combined cocultivation with virulent and avirulent strains of Agrobacterium

SummaryFour detection techniques, three of which gave reliable identification of the virus particles, were used to locate potato leafroll virus (PLRV) in the alimentary canal of its main aphid vector,Myzus persicae Sulz: immunofluorescence on cryostat sections, conventional transmission electron microscopy on ultrathin sections and immune electron microscopy with gold labeling, either prior to or after fixation-embedding. Each method clearly showed the presence of the virus in the intestine epithelium and its absence in cells of the other parts of the alimentary canal. Under the experimental conditions used, the intestinal cells seemed to be the pathway for PLRV transport from the gut lumen into the haemocoel. Electron microscopy examinations showed many virus particles close to the apical plasmalemma of the epithelial cells in the gut lumen of the intestine. Other particles were seen in shallow pit-like regions or surrounded by coated vesicles in the apical part of these cells. Thus the virus particles seemed to enter the epithelial cells of the intestine by a mechanism of endocytosis. In the cytoplasm of these cells, virions were also frequently observed in isolated — or more often aggregated — tubular vesicles. The latter could be involved in PLRV transport through the cell since they were observed fusing with different cell organelles. A few viral particles were also detected in lysosomes as well as in multivesicular bodies. Virus particles were observed between the plasmalemma and basal lamina of the intestine cells but not in the haemocoel, where probably they were quickly dispersed. Our results are discussed in relation to other reports which have shown hindgut and stomach as sites of passage from the gut lumen into the aphids body cavity for PLRV and other circulative viruses.

Incidence of potato viruses and characterisation of Potato virus Y variability in late season planted potato crops in Northern Tunisia

SummaryTen PVY isolates representative of four PVY groups (YN, YNTN, YN-W, Y O), differing by their ability to induce reactions of vein necrosis on tobacco and tuber necrosis on potato, were studied in order to research the regions of the viral genome involved in these necrosis phenomena. The whole genome of these isolates was amplified in two fragments (4 063 and 5 670 nucleotides) and was subjected to a restriction fragment length polymorphism (RFLP) study. In the first 4 063 nucleotides of the PVY genome, a phenetic analysis of RFLP data resulted in a clustering of our PVY isolates into three groups: PVYN isolates (group A); PVYNTN and PVYN-W isolates (group B) and PVYO isolates (group C). In the last 5 670 nucleotides, two groups were found: PVYN and PVYNTN isolates (group D) and PVYO and PVYN-W isolates (group E). From this clustering and the necrosing properties known for theseisolates, the tobacco necrosis determinants seem more likely located inthe 5′ than in the 3′ half part of the viral RNA, whereas it would be theopposite situation for the determinants of the necrosis on potato tubers.Moreover a recombination event seemed to have occurred in the genome ofthe PVYN-W isolates.