Research conducted by the Laboratory of Nematology is part of the research program of the Graduate School Experimental Plant Sciences (EPS) and C.T. de Wit Graduate School for Production Ecology & Resource Conservation (PE&RC)
R genes: Evolutionary dynamics and functional constraints
Our focus is the identification and functional characterization of (nematode) resistance genes and their homologs in Solanum species. Sequence conservation between the NB-ARC domain of the R genes Gpa2 and Rx1 suggests a similar resistance mechanism. However, these closely related genes induce resistance against completely unrelated pathogens as Rx confers extreme resistance against the potato virus X (PVX) and Gpa2 confers a mild resistance response to the potato cyst nematode Globodera pallida. To gain more insight in the resistancce mechanism and structure-function relationships of Gpa2 and Rx1, a series of gene expression studies are conducted as well as the construction of a series recombinant R genes by domain swapping pointing out the functional constraints of pathogen recognition. In addition, subcellular localization of the proteins is performed in order to know more about the spatial and temporal dynamics of these R proteins. For a better understanding of the evolution of this complex disease resistance locus, additional (functional) Rx1 orthologues have been isolated from wild species throughout Solanum. Sequence analysis showed that the LRR regions of the functional Rx alleles are virtual identical supporting the role of this domain in pathogen recognition. Furthermore, we have shown that Rx specificity is derived from one ancestral gene, and that Rx mediated PVX recognition are befor Solanum series Tuberosa and Acaulia diverged. Finally, twelve homologous NBS-LRR genes were identified as candidates for being the H1 gene, which are now being tested in complementation assay to see if they confer nematode resistance. For identification of the putative avirulence factor of the H1 gene four thousand ESTs were generated and analyzed from a cDNA library of the avirulent infective stage of Globodera rostochiensis. Interesting candidate genes encodign secretory proteins were selected for the identification of polymorfisms between the avirulent and virulent nematodes lines 19 and 22.