JXB Advance Access originally published online on September 19, 2005
Journal of Experimental Botany 2005 56(421):2925-2933; doi:10.1093/jxb/eri288
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RESEARCH PAPER |
The products of the broken Tm-2 and the durable Tm-22 resistance genes from tomato differ in four amino acids
Department Molecular Biology of Plants, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN, Haren, The Netherlands
* To whom correspondence should be addressed at: Laboratory of Plant Physiology, University of Groningen, PO Box 14, 9750 AA, Haren, The Netherlands. Fax: +31 50 3632273, E-mail: f.c.lanfermeijer{at}rug.nl
To gain an insight into the processes underlying disease resistance and its durability, the durable Tm-22 resistance gene was compared with the broken Tm-2 resistance gene. The Tm-2 gene of tomato could be isolated via PCR with primers based on the Tm-22 sequence. The Tm-2 gene, like the Tm-22 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-22 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-22) 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.
Key words: Lycopersicon esculentum, Lycopersicon peruvianum, Tm-2, Tm-22, tomato mosaic virus, plant disease resistance gene, durability, structure–function relationships