Identification of new isolates of Turnip mosaic virus that cluster with less common viral strains.

Turnip mosaic virus (TuMV) was found infecting cultivated brassicas and wild and cultivated ornamental Brassicaceae plants in different regions of Spain. Five new TuMV isolates, originating from different host plant species (Brassica cretica, Brassica juncea, Brassica napus, Eruca vesicaria subsp. sativa and Sisymbrium orientale), have been identified. The nucleotide sequences of the coat protein (CP) genes of the five isolates were determined. Phylogenetic analysis of the CP sequences showed that the five isolates grouped into two different clusters. The three isolates from the central region of Spain clustered with a previously reported Pisum sativum isolate from southeastern Spain, whereas the other two isolates from the eastern region clustered with two Italian and two Greek isolates. Both clusters were genetically distinct and belonged to the multi-lineage group OBR. The OBR group contains mainly TuMV isolates from hosts other than Brassica spp. and Raphanus sativus and mostly originating from Mediterranean countries. These new sequences provide further phylogenetic resolution of the OBR group. Although new TuMV isolates have been found in Spain, they were not associated with any serious disease outbreaks.

The phylogeny of Turnip mosaic virus; comparisons of 38 genomic sequences reveal a Eurasian origin and a recent 'emergence' in east Asia.

The genomes of a representative world-wide collection of 32 Turnip mosaic virus (TuMV) isolates were sequenced and these, together with six previously reported sequences, were analysed. At least one-fifth of the sequences were recombinant. In phylogenetic analyses, using genomic sequences of Japanese yam mosaic virus as an outgroup, the TuMV sequences that did not show clear recombination formed a monophyletic group with four well-supported lineages. These groupings correlated with differences in pathogenicity and provenance; the sister group to all others was of Eurasian B-strain isolates from nonbrassicas, and probably represents the ancestral TuMV population, and the most recently 'emerged' branch of the population was probably that of the BR-strain isolates found only in east Asia. Eight isolates, all from east Asia, were clear recombinants, probably the progeny of recent recombination events, whereas a similar number, from other parts of the world, were seemingly older recombinants. This difference indicates that the presence of clear recombinants in a subpopulation may be a molecular signature of a recent 'emergence'.

Strains of Turnip mosaic potyvirus as defined by the molecular analysis of the coat protein gene of the virus.

Turnip mosaic virus (TuMV) is a member of the potyvirus genus with a wide host range and highly variable in its biological characteristics. Analysis of the CP gene sequences from databases, combined with the experimental analysis of the CP gene of further isolates, using data derived from sequence or restriction analysis, has allowed the genetic classification of 60 TuMV isolates or sequences. Two main genetic clusters MB (mostly Brassica isolates) and MR (mostly Radish isolates) were found, together with several apparently independent lineages. Isolates in the latter could be grouped as Intermediate between Brassica and Radish clusters (IBR) or outside Brassica and Radish clusters (OBR), according to their genetic distance to the main clusters. The genetic diversity of TuMV isolates deposited in the databases was increased with the sequences of the CP gene of seven selected isolates, mainly belonging to IBR or OBR groups. There was a correlation between the MR genetic cluster and JPN 1 serotype.

The cylindrical inclusion gene of Turnip mosaic virus encodes a pathogenic determinant to the Brassica resistance gene TuRB01.

The viral component of Turnip mosaic virus (TuMV) determining virulence to the Brassica napus TuRB01 dominant resistance allele has been identified. Sequence comparisons of an infectious cDNA clone of the UK 1 isolate of TuMV (avirulent on TuRB01) and a spontaneous mutant capable of infecting plants possessing TuRB01 suggested that a single nucleotide change in the cylindrical inclusion (CI) protein coding region (gene) of the virus was responsible for the altered phenotype. A second spontaneous mutation involved a different change in the CI gene. The construction of chimeric genomes and subsequent inoculations to plant lines segregating for TuRB01 confirmed the involvement of the CI gene in this interaction. Site-directed mutagenesis of the viral coat protein (CP) gene at the ninth nucleotide was carried out to investigate its interaction with TuRB01. The identity of this nucleotide in the CP gene did not affect the outcome of the viral infection. Both mutations identified in the CI gene caused amino acid changes in the C terminal third of the protein, outside any of the conserved sequences reported to be associated with helicase or cell-to-cell transport activities. This is the first example of a potyvirus CI gene acting as a determinant for a genotype-specific resistance interaction.