Homologues of a single resistance-gene cluster in potato confer resistanceto distinct pathogens: a virus and a nematode

The isolation of the nematode-resistance gene Gpa2 in potato is described, and it is demonstrated that highly homologous resistance genes of a single resistance-gene cluster can confer resistance to distinct pathogen species. Molecular analysis of the Gpa2 locus resulted in the identification of an R-gene cluster of four highly homologous genes in a region of approximately 115 kb. At least two of these genes are active: one corresponds to the pre viously isolated Rx1 gene that confers resistance to potato virus X, while the other corresponds to the Gpa2 gene that confers resistance to the potat o cyst nematode Globodera pallida. The proteins encoded by the Gpa2 and the Rx1 genes share an overall homology of over 88% (amino-acid identity) and belong to the leucine-zipper, nucleotide-binding site, leucine-rich repeat (LZ-NBS-LRR)-containing class of plant resistance genes. From the sequence conservation between Gpa2 and Rx1 it is clear that there is a direct evolut ionary relationship between the two proteins. Sequence diversity is concent rated in the LRR region and in the C-terminus. The putative effector domain s are more conserved suggesting that, at least in this case, nematode and v irus resistance cascades could share common components. These findings unde rline the potential of protein breeding for engineering new resistance spec ificities against plant pathogens in vitro.