Nucleotide sequence analysis of the movement genes of resistance breaking strains of tomato mosaic virus.

The nucleotide sequences were determined for the movement genes, encoding 30K proteins, of two resistance breaking strains of tomato mosaic virus (ToMV), LII-ToMV and LIIA-ToMV. The putative amino acid sequences of the encoded proteins were compared with L-ToMV and with two previously published resistance breaking strains, Ltb1-ToMV and C32-ToMV. LII-ToMV, a Type 2 strain able to infect tomatoes containing the Tm-2 gene, has four amino acid changes relative to L-ToMV. One of these substitutions, Glu-Lys133, is also found in the other Type 2 strains, Ltb1-ToMV and C32-ToMV. LIIA-ToMV, a Type 2(2) strain able to overcome the resistance conferred by the tomato Tm-2(2) gene, has four amino acid differences from L-ToMV. The Type 2(2) strain has no substitutions in common with any of the Type 2 strains; however the predominance of amino acid substitutions that involve a change in the local charge (six out of the eight) suggests an electrostatic interaction between a host factor and the 30K protein may be intrinsic to the function of the movement gene and/or resistance breakage.