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
Solanum pennellii is a wild tomato species endemic to Andean regions in South America, where it has evolved to thrive in arid habitats. Because of its extreme stress tolerance and unusual morphology, it is an important donor of germplasm for the cultivated tomato Solanum lycopersicum. Introgression lines (ILs) in which large genomic regions of S. lycopersicum are replaced with the corresponding segments from S. pennellii can show remarkably superior agronomic performance. Here we describe a high-quality genome assembly of the parents of the IL population. By anchoring the S. pennellii genome to the genetic map, we define candidate genes for stress tolerance and provide evidence that transposable elements had a role in the evolution of these traits. Our work paves a path toward further tomato improvement and for deciphering the mechanisms underlying the myriad other agronomic traits that can be improved with S. pennellii germplasm.
Assuntos
Genoma de Planta , Solanum/genética , Estresse Fisiológico/genética , Mapeamento Cromossômico/métodos , Cromossomos de Plantas , Elementos de DNA Transponíveis , Locos de Características QuantitativasRESUMO
Ongoing genomics projects of tomato (Solanum lycopersicum) and potato (S. tuberosum) are providing unique tools for comparative mapping studies in Solanaceae. At the chromosomal level, bacterial artificial chromosomes (BACs) can be positioned on pachytene complements by fluorescence in situ hybridization (FISH) on homeologous chromosomes of related species. Here we present results of such a cross-species multicolor cytogenetic mapping of tomato BACs on potato chromosomes 6 and vice versa. The experiments were performed under low hybridization stringency, while blocking with Cot-100 was essential in suppressing excessive hybridization of repeat signals in both within-species FISH and cross-species FISH of tomato BACs. In the short arm we detected a large paracentric inversion that covers the whole euchromatin part with breakpoints close to the telomeric heterochromatin and at the border of the short arm pericentromere. The long arm BACs revealed no deviation in the colinearity between tomato and potato. Further comparison between tomato cultivars Cherry VFNT and Heinz 1706 revealed colinearity of the tested tomato BACs, whereas one of the six potato clones (RH98-856-18) showed minor putative rearrangements within the inversion. Our results present cross-species multicolor BAC-FISH as a unique tool for comparative genetic studies across Solanum species.