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

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

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Systems Maintenance, Monday, 15th February 2010

Wiley InterScience

The Plant Journal

Volume 44 Issue 2, Pages 208 - 222

Published Online: 27 Sep 2005

Published in association with the Society for Experimental Biology

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

Edwin A.G. van der Vossen ^1,*, Jack Gros ² , Anne Sikkema ² , Marielle Muskens ² , Doret Wouters ¹ , Petra Wolters ^1,† , Andy Pereira ¹ and Sjefke Allefs ²

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

Correspondence to *(fax +31 317 418094; e-mail edwin.vandervossen@wur.nl).

^† Present address: Crop Genetics, DuPont Experimental Station, PO Box 80353, Wilmington, DE 19880-0353, USA.

KEYWORDS

Rpi-blb2 • disease resistance • Phytophthora infestans • Solanum bulbocastanum • potato • late blight

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.