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, 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.