Characterization of the Tm-2 locus of tomato and its durability

PhD ceremony: Mr. I. Rasul, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Characterization of the Tm-2 locus of tomato and its durability

Promotor(s): prof. J. Hille

Faculty: Mathematics and Natural Sciences

Tobamo-viruses are common pathogens of many crop plants. To date four ToMV resistance genes, the N, Tm-1, Tm-2 and Tm-2² genes Ijaz Rasul has isolated, characterized and transgenically expressed in tobacco and tomato. However, since almost five decades, the Tm-2² gene which is an allele of the Tm-2 gene has been conferring durable resistance. Their encoded proteins differ in only four amino acids spreading over two regions. Domain shuffling between both proteins and site-directed mutagenesis show that one region regulates the specificity and the other is involved in the signal transduction. Moreover only one amino acid change is responsible for the Tm-2² resistance specificity.

The extra-family transfer of the Tm-2² gene in Arabidopsis is also studied. Although the introduction of virus resistance could not be fully achieved, this suggests expression of the Tm-2² gene and interaction of the R-protein with host factors.

To search for new or Tm-2² homologous resistances from-outside the agronomic gene pool, 17 Solanum species have been analyzed for their ToMV resistance by Rasul. Six genotypes were selected for further molecular analysis. From all genes could be isolated resembling the Tm-2² . Three of those do not show any resistance, two show a Tm-2-like, while one truncated gene displays a Tm-2² -like resistance. For future research, the results of the extra-family transfer of the Tm-2² gene and truncated homologue of this gene might be valuable tools for plant molecular biologists. This may increase the TMV resistance gene pool and may lead to a further understanding of plant-virus interaction mechanisms.