Free Content The Rpi-blb2 gene from Solanum bulbocastanum is an Mi-1 gene homolog conferring broad-spectrum late blight resistance in potato

Authors: Vossen, Edwin A.G.; Gros, Jack1; Sikkema, Anne1; Muskens, Marielle1; Wouters, Doret2; Wolters, Petra; Pereira, Andy2; Allefs, Sjefke1

Source: The Plant Journal, Volume 44, Number 2, October 2005 , pp. 208-222(15)

Publisher: Blackwell Publishing

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Abstract:

Summary

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.

Keywords: Rpi-blb2; disease resistance; Phytophthora infestans; Solanum bulbocastanum; potato; late blight

Document Type: Research article

DOI: 10.1111/j.1365-313X.2005.02527.x

Affiliations: 1: Agrico Research, PO Box 40, 8300 AA Emmeloord, The Netherlands 2: Plant Research International BV, PO Box 16, 6700 AA Wageningen, The Netherlands, and

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