RESUMO
Plants have evolved a limited repertoire of NB-LRR disease resistance (R) genes to protect themselves against myriad pathogens. This limitation is thought to be counterbalanced by the rapid evolution of NB-LRR proteins, as only a few sequence changes have been shown to be sufficient to alter resistance specificities toward novel strains of a pathogen. However, little is known about the flexibility of NB-LRR R genes to switch resistance specificities between phylogenetically unrelated pathogens. To investigate this, we created domain swaps between the close homologs Gpa2 and Rx1, which confer resistance in potato (Solanum tuberosum) to the cyst nematode Globodera pallida and Potato virus X, respectively. The genetic fusion of the CC-NB-ARC of Gpa2 with the LRR of Rx1 (Gpa2CN/Rx1L) results in autoactivity, but lowering the protein levels restored its specific activation response, including extreme resistance to Potato virus X in potato shoots. The reciprocal chimera (Rx1CN/Gpa2L) shows a loss-of-function phenotype, but exchange of the first three LRRs of Gpa2 by the corresponding region of Rx1 was sufficient to regain a wild-type resistance response to G. pallida in the roots. These data demonstrate that exchanging the recognition moiety in the LRR is sufficient to convert extreme virus resistance in the leaves into mild nematode resistance in the roots, and vice versa. In addition, we show that the CC-NB-ARC can operate independently of the recognition specificities defined by the LRR domain, either aboveground or belowground. These data show the versatility of NB-LRR genes to generate resistance to unrelated pathogens with completely different lifestyles and routes of invasion.
Assuntos
Resistência à Doença/genética , Doenças das Plantas/imunologia , Proteínas de Plantas/metabolismo , Potexvirus/fisiologia , Solanum tuberosum/genética , Tylenchoidea/fisiologia , Animais , Proteínas de Repetições Ricas em Leucina , Mutação com Perda de Função , Fenótipo , Doenças das Plantas/parasitologia , Doenças das Plantas/virologia , Folhas de Planta/genética , Folhas de Planta/imunologia , Folhas de Planta/parasitologia , Folhas de Planta/virologia , Proteínas de Plantas/genética , Raízes de Plantas/genética , Raízes de Plantas/imunologia , Raízes de Plantas/parasitologia , Raízes de Plantas/virologia , Brotos de Planta/genética , Brotos de Planta/imunologia , Brotos de Planta/parasitologia , Brotos de Planta/virologia , Domínios Proteicos , Proteínas/genética , Proteínas/metabolismo , Receptores Imunológicos/genética , Receptores Imunológicos/metabolismo , Proteínas Recombinantes de Fusão , Solanum tuberosum/imunologia , Solanum tuberosum/parasitologia , Solanum tuberosum/virologiaRESUMO
The Grp1 locus confers broad-spectrum resistance to the potato cyst nematode species Globodera pallida and Globodera rostochiensis and is located in the GP21-GP179 interval on the short arm of chromosome V of potato. A high-resolution map has been developed using the diploid mapping population RHAM026, comprising 1,536 genotypes. The flanking markers GP21 and GP179 have been used to screen the 1,536 genotypes for recombination events. Interval mapping of the resistances to G. pallida Pa2 and G. rostochiensis Ro5 resulted in two nearly identical LOD graphs with the highest LOD score just north of marker TG432. Detailed analysis of the 44 recombinant genotypes showed that G. pallida and G. rostochiensis resistance could not be separated and map to the same location between marker SPUD838 and TG432. It is suggested that the quantitative resistance to both nematode species at the Grp1 locus is mediated by one or more tightly linked R genes that might belong to the NBS-LRR class.