Journal Article

The major resistance gene cluster in lettuce is highly duplicated and spans several megabases

Sivaramakrishnan, S, Shen, K A, Chin, D B, Michelmore, R W, Lavelle, D O, Meyers, B C, Zhang, Z

1998

Overview

At least 10 Dm genes conferring resistance to the oomycete downy mildew fungus Bremia lactucae map to the major resistance cluster in lettuce. We investigated the structure of this cluster in the lettuce cultivar Diana, which contains Dm3. A deletion breakpoint map of the chromosomal region flanking Dm3 was saturated with a variety of molecular markers. Several of these markers are components of a family of resistance gene candidates (RGC2) that encode a nucleotide binding site and a leucine-rich repeat region. These motifs are characteristic of plant disease resistance genes. Bacterial artificial chromosome clones were identified by using duplicated restriction fragment length polymorphism markers from the region, including the nucleotide binding site-encoding region of RGC2. Twenty-two distinct members of the RGC2 family were characterized from the bacterial artificial chromosomes; at least two additional family members exist. The RGC2 family is highly divergent; the nucleotide identity was as low as 53% between the most distantly related copies. These RGC2 genes span at least 3.5 Mb. Eighteen members were mapped on the deletion breakpoint map. A comparison between the phylogenetic and physical relationships of these sequences demonstrated that closely related copies are physically separated from one another and indicated that complex rearrangements have shaped this region. Analysis of low-copy genomic sequences detected no genes, including RGC2, in the Dm3 region, other than sequences related to retrotransposons and transposable elements. The related but divergent family of RGC2 genes may act as a resource for the generation of new resistance phenotypes through infrequent recombination or unequal crossing over

• Publisher: American Society of Plant Biologists,American Society of Plant Physiologists
• Subject: ADN / Airborne microorganisms / AMPLIFIED FRAGMENT LENGTH POLYMORPHISM / Base Sequence / BREMIA LACTUCAE / CARTE GENETIQUE / Chromosome Mapping / CHROMOSOME MAPS / Chromosomes / Chromosomes, Bacterial / Chromosomes, Bacterial - genetics / Cloning, Molecular / Cultivars / DELETION BREAKPOINT MAPS / DELETIONS / DISEASE RESISTANCE / DNA / DNA Primers / DNA Primers - genetics / Evolution, Molecular / Evolutionary genetics / Gels / GENBANK/AF072267 / GENBANK/AF072268 / GENBANK/AF072269 / GENBANK/AF072270 / GENBANK/AF072271 / GENBANK/AF072272 / GENBANK/AF072273 / GENBANK/AF072274 / GENBANK/AF072275 / GENBANK/AF072276 / GENBANK/AF072277 / GENBANK/AF072278 / GENBANK/AF072279 / GENBANK/AF072280 / GENBANK/AF072281 / GENBANK/AF072282 / GENBANK/AF072283 / GENBANK/AF072284 / GENBANK/AF072285 / GENBANK/AF072286 / GENBANK/AF072287 / GENBANK/AF072288 / GENE / Gene Duplication / Gene Rearrangement / GENES / Genes, Plant / Genetic loci / GENETIC MAPPING / GENETIC MAPS / GENETIC MARKERS / GENETIC RESISTANCE / genetics / Genomics / INTERGENIC DNA / Lactuca - genetics / Lactuca - microbiology / LACTUCA SATIVA / Lettuce / LOCI / LOCUS / MAPAS GENETICOS / MARCADORES GENETICOS / MARQUEUR GENETIQUE / Medical genetics / microbiology / MOLECULAR SEQUENCE DATA / MULTIGENE FAMILIES / Multigene Family / MUTANT / MUTANTES / MUTANTS / NUCLEOTIDE SEQUENCE / nucleotide sequences / Oomycetes / Oomycetes - pathogenicity / pathogenicity / PHYLOGENETICS / Phylogeny / Plant cells / Plant Diseases / Plant Diseases - genetics / Plant Diseases - microbiology / Polymerase Chain Reaction / Polymorphism, Restriction Fragment Length / RANDOM AMPLIFIED POLYMORPHIC DNA / random amplified polymorphic DNA technique / RAPD / RESISTANCE AUX MALADIES / RESISTANCE GENETIQUE / RESISTENCIA A LA ENFERMEDAD / RESISTENCIA GENETICA / RGC2 GENES / SECUENCIA NUCLEOTIDICA / SEQUENCE NUCLEOTIDIQUE