The double-resistance-breaking Tomato mosaic virus strain ToMV1-2 contains two independent single resistance-breaking domains.

Tomato mosaic virus (ToMV) causes a serious loss of yield and fruit quality in tomato crops. To control ToMV, three resistance genes, Tm-1, Tm-2, and Tm-2(2) from wild tomato species were introduced into commercial tomato cultivars. Soon after, however, single and, rarely, double-resistance-breaking virus strains for Tm-1 and Tm-2 emerged. Sequence analysis of a Tm-1/Tm-2 double-resistance-breaking virus, designated ToMV1-2, revealed 30 nucleotide substitutions compared with wild-type ToMV. Of these, six substitutions result in amino acid exchanges. Two exchanges are in the methyl transferase/helicase domain of the ToMV1-2 130/180-kDa proteins (D-1097 to V, R-1100 to Q), two exchanges are found in the 30-kDa movement protein (MP; E-52 to K, E-133 to K), and two exchanges are in the coat protein (I-22 to V, A-87 to S). Construction of chimeric full-length viral cDNA clones containing the base substitutions resulting in altered amino acids, either in the 130/180 kDa proteins or the MP, revealed that the amino acid exchanges in the 130/180-kDa proteins enable ToMV1-2 to break the Tm-1 resistance, while those in the MP enable ToMV1-2 to overcome the Tm-2 resistance. Furthermore, a novel Tm-1/Tm-2 double-resistance-breaking virus was generated by combining the Tm-1-breaking domain of ToMV1-2 and the MP of a new virus, ToMV2, containing the amino acid exchanges E-133 to K and N-135 to S. Together, the data suggest that double-resistance-breaking ToMV1-2 may have resulted from recombination between Tm-1 and Tm-2 single resistance-breaking virus strains.

Identification of bovine enteric Caliciviruses (BEC) from cattle in Baden-Württemberg.

Caliciviruses are known to cause different diseases in many animal species. The bovine enteric caliciviruses (BEC) are associated with diarrhoea in cattle. These viruses have been classified in the genus Norovirus and are closely related to human noroviruses, the leading cause of gastroenteritis in humans. This has raised questions about zoonotic transmission and an animal reservoir for the human viruses. Two samples from 41 stool samples collected for diagnostic purposes from diarrheic cattle in Aulendorf, Germany tested positive for BEC. The samples were amplified with new degenerate BEC specific primers, which amplify a 263 bp portion of the RNA polymerase region. Analysis of the nucleotide sequences showed that these viruses are most closely related to the Norovirus genogroup III/2 (Bo/NLV/Newbury-2/76/UK) viruses.

The Tomato mosaic virus 30 kDa movement protein interacts differentially with the resistance genes Tm-2 and Tm-2(2).

In tomato plants ( Lycopersicon esculentum Mill.), the genes Tm-2 and Tm-2(2) confer resistance to Tomato mosaic virus (ToMV). Sequence analysis of ToMV strains able to break the Tm-2 or Tm-2(2) resistance revealed distinct amino acid exchanges in the viral 30 kDa protein, suggesting that the movement protein is recognized by both resistance genes to induce the plant defense reaction. To analyze the interactions between the ToMV movement protein and the Tm-2 and Tm-2(2) genes in detail, we generated transgenic tomato lines expressing various movement protein gene constructs. Crosses of the transgenic tomato lines with cultivars containing either the Tm-2 or the Tm-2(2) gene demonstrated that both genes are able to elicit a hypersensitive reaction in response to movement proteins from resistance inducing ToMV strains. However, the domains and the structural requirements for induction of the necrotic response by the ToMV movement protein are completely different for either resistance gene. In the context of the Tm-2 gene, the resistance determinant lies within the N-terminal 188 amino acids of the ToMV movement protein. Interaction of the 30 kDa protein with the Tm-2(2) gene requires two distinct domains localized at the C-terminus and in a different region of the protein, respectively.