title: The tandem repeated organization of NB-LRR genes in the clubroot-resistant CRb locus in Brassica rapa L.
abstract: To facilitate prevention of clubroot disease, a major threat to the successful cultivation of Chinese cabbage (Brassica rapa L.), we bred clubroot-resistant (CR) cultivars by introducing resistance genes from CR turnips via conventional breeding. Among 11 CR loci found in B. rapa, we identified CRb in Chinese cabbage cultivar 'CR Shinki' as a single dominant gene for resistance against Plasmodiophora brassicae pathotype group 3, against which the stacking of Crr1 and Crr2 loci was not effective. However, the precise location and pathotype specificity of CRb have been controversial, because CRa and Rcr1 also map near this locus. Previously, our fine-mapping study revealed that CRb is located in a 140-kb genomic region on chromosome A03. Here, we determined the nucleotide sequence of an approximately 64-kb candidate region in the resistant line; this region contains six open reading frames (ORFs) similar to NB-LRR encoding genes that are predicted to occur in tandem with the same orientation. Among the six ORFs present, only four on the genome of the resistant line showed a strong DNA sequence identity with each other, and only one of those four could confer resistance to P. brassicae isolate No. 14 of the pathotype group 3. These results suggest that these genes evolved through recent gene duplication and uneven crossover events that could lead to the acquisition of clubroot resistance. The DNA sequence of the functional ORF was identical to that of the previously cloned CRa gene; thus, we showed that the independently identified CRb and CRa are one and the same clubroot-resistance gene.
authors.affiliation: Institute of Vegetable and Floriculture Science, NARO, 360 Kusawa, Ano, Tsu, Mie, 514-2392, Japan. khatake@iwate-u.ac.jp.|Faculty of Agriculture, Iwate University, 3-18-8 Ueda, Morioka, Iwate, 020-8550, Japan. khatake@iwate-u.ac.jp.
authors.forename: Katsunori
authors.initials: K
authors.lastname: Hatakeyama
authors.affiliation: Institute of Vegetable and Floriculture Science, NARO, 360 Kusawa, Ano, Tsu, Mie, 514-2392, Japan.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Niwa
authors.affiliation: Institute of Vegetable and Floriculture Science, NARO, 360 Kusawa, Ano, Tsu, Mie, 514-2392, Japan.|Nippon Norin Seed Co., Ltd., 6-6-5 Takinogawa, Kita-ku, Tokyo, 114-0023, Japan.
authors.forename: Takeyuki
authors.initials: T
authors.lastname: Kato
authors.affiliation: Institute of Vegetable and Floriculture Science, NARO, 360 Kusawa, Ano, Tsu, Mie, 514-2392, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Ohara
authors.affiliation: Institute of Vegetable and Floriculture Science, NARO, 360 Kusawa, Ano, Tsu, Mie, 514-2392, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Kakizaki
authors.affiliation: Institute of Vegetable and Floriculture Science, NARO, 360 Kusawa, Ano, Tsu, Mie, 514-2392, Japan.|Tohoku Agricultural Research Center, NARO, 4 Akahira, Shimo-kuriyagawa, Morioka, Iwate, 020-0198, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Matsumoto
mesh_terms: D001483:Base Sequence; D029741:Brassica rapa / Q000235:genetics* / Q000469:parasitology; D002874:Chromosome Mapping; D015723:Gene Library; D005799:Genes, Dominant; D017343:Genes, Plant; D005822:Genetic Vectors; D016366:Open Reading Frames; D010641:Phenotype; D020161:Physical Chromosome Mapping; D010935:Plant Diseases / Q000235:genetics*; D056909:Plasmodiophorida; D017422:Sequence Analysis, DNA; D020080:Tandem Repeat Sequences
keywords: Brassica rapa; Clubroot; Duplication; NB-LRR; Plasmodiophora brassicae; Resistant gene