title: The Rpi-blb2 gene from Solanum bulbocastanum is an Mi-1 gene homolog conferring broad-spectrum late blight resistance in potato.
abstract: The necessity to develop potato and tomato crops that possess durable resistance against the oomycete pathogen Phytophthora infestans is increasing as more virulent, crop-specialized and pesticide resistant strains of the pathogen are rapidly emerging. Here, we describe the positional cloning of the Solanum bulbocastanum-derived Rpi-blb2 gene, which even when present in a potato background confers broad-spectrum late blight resistance. The Rpi-blb2 locus was initially mapped in several tetraploid backcross populations, derived from highly resistant complex interspecific hybrids designated ABPT (an acronym of the four Solanum species involved:S. acaule, S. bulbocastanum, S. phureja and S. tuberosum), to the same region on chromosome 6 as the Mi-1 gene from tomato, which confers resistance to nematodes, aphids and white flies. Due to suppression of recombination in the tetraploid material, fine mapping was carried out in a diploid intraspecific S. bulbocastanum F1 population. Bacterial artificial chromosome (BAC) libraries, generated from a diploid ABPT-derived clone and from the resistant S. bulbocastanum parent clone, were screened with markers linked to resistance in order to generate a physical map of the Rpi-blb2 locus. Molecular analyses of both ABPT- and S. bulbocastanum-derived BAC clones spanning the Rpi-blb2 locus showed it to harbor at least 15 Mi-1 gene homologs (MiGHs). Of these, five were genetically determined to be candidates for Rpi-blb2. Complementation analyses showed that one ABPT- and one S. bulbocastanum-derived MiGH were able to complement the susceptible phenotype in both S. tuberosum and tomato. Sequence analyses of both genes showed them to be identical. The Rpi-blb2 protein shares 82% sequence identity to the Mi-1 protein. Significant expansion of the Rpi-blb2 locus compared to the Mi-1 locus indicates that intrachromosomal recombination or unequal crossing over has played an important role in the evolution of the Rpi-blb2 locus. The contrasting evolutionary dynamics of the Rpi-blb2/Mi-1 loci in the two related genomes may reflect the opposite evolutionary potentials of the interacting pathogens.
authors.affiliation: Plant Research International BV, PO Box 16, 6700 AA Wageningen, The Netherlands. edwin.vandervossen@wur.nl
authors.forename: Edwin A G
authors.initials: EA
authors.lastname: van der Vossen
authors.forename: Jack
authors.initials: J
authors.lastname: Gros
authors.forename: Anne
authors.initials: A
authors.lastname: Sikkema
authors.forename: Marielle
authors.initials: M
authors.lastname: Muskens
authors.forename: Doret
authors.initials: D
authors.lastname: Wouters
authors.forename: Petra
authors.initials: P
authors.lastname: Wolters
authors.forename: Andy
authors.initials: A
authors.lastname: Pereira
authors.forename: Sjefke
authors.initials: S
authors.lastname: Allefs
mesh_terms: D000595:Amino Acid Sequence; D032461:Chromosomes, Plant / Q000235:genetics; D003001:Cloning, Molecular; D017343:Genes, Plant / Q000235:genetics*; D005816:Genetic Complementation Test; D008040:Genetic Linkage; D008969:Molecular Sequence Data; D020161:Physical Chromosome Mapping; D010838:Phytophthora / Q000502:physiology*; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D032322:Solanum / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology*
chemical_list: D010940:Plant Proteins