The products of the durable Tm-2 ( 2 ) and the broken Tm-2 resistance genes from tomato differ in four amino acids

To gain an insight into the processes underlying disease resistance and its durability, the durable Tm2 resistance gene was compared with the broken Tm2 resistance gene. The Tm-2 gene of tomato could be isolated via PCR with primers based on the Tm-2 sequence. The Tm-2 gene, like the Tm-2 gene, encodes an 861 amino acid polypeptide, which belongs to the coiled coil/nucleotide binding site/leucine-rich repeat class of resistance proteins. The functionality and the nature of the isolated Tm-2 gene were confirmed by introducing the gene under the control of the 35S promoter into tomato mosaic virus-susceptible tobacco. This transgenic tobacco was crossed with transgenic tobacco plants producing the movement protein (MP)-authenticated MP as the Avr protein of the Tm-2 resistance. The Tm-2 and Tm-2 open reading frames only differ in seven nucleotides, which on a protein level results in four amino acid differences, of which two are located in the nucleotide binding site and two are located in the leucine-rich repeat domain. The small difference between the two proteins suggests a highly similar interaction of these proteins with the MP, which has major implications for the concept of durability. Comparison of the two resistance-conferring alleles (Tm-2 and Tm-2) with two susceptible alleles (tm-2 and lptm-2) allowed discussion of the structure–function relationship in the Tm-2 proteins. It is proposed that the Tm-2 proteins display a partitioning of the leucine-rich repeat domain, in which the N-terminal and C-terminal parts function in signal transduction and MP recognition, respectively.