Genetics. Published Articles Ahead of Print: October 20, 2008, Copyright © 2008
doi:10.1534/genetics.108.095034


A more recent version of this article appeared on December 1, 2008.

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Two Adjacent NBS-LRR Class Genes are Required to Confer Pikm-specific Rice Blast Resistance

Ikuo Ashikawa 1*, Nagao Hayashi 2, Hiroko Yamane 3, Hiroyuki Kanamori 3, Jianzhong Wu 2, Takashi Matsumoto 2, Kazuko Ono 2 and Masahiro Yano 2

1 National Institute of Crop Science
2 National Institute of Agrobiological Sciences
3 Institute of the Society for Techno-Innovation of Agriculture, Forestry, and Fisheries

* To whom correspondence should be addressed. E-mail: ashikawa{at}affrc.go.jp.

Submitted on August 9, 2008
Revised on September 23, 2008
Accepted on 15 October 2008


Abstract

The rice blast resistance gene Pikm was cloned by a map-based cloning strategy. High-resolution genetic mapping and sequencing of the gene region in the Pikm-containing cultivar Tsuyuake narrowed down the candidate region to a 131-kb genomic interval. Sequence analysis predicted two adjacently arranged resistance-like genes, Pikm1-TS and Pikm2-TS, within this candidate region. These genes encoded proteins with a nucleotide-binding site (NBS) and leucine-rich repeats (LRRs) and were considered the most probable candidates for Pikm. However, genetic complementation analysis of transgenic lines individually carrying these two genes negated the possibility that either Pikm1-TS or Pikm2-TS alone was Pikm. Instead, it was revealed that transgenic lines carrying both of these genes expressed blast resistance. The results of the complementation analysis and an evaluation of the resistance specificity of the transgenic lines to blast isolates demonstrated that Pikm-specific resistance is conferred by cooperation of Pikm1-TS and Pikm2-TS. Although these two genes are not homologous with each other, they both contain all the conserved motifs necessary for an NBS-LRR class gene to function independently as a resistance gene.

Key Words: Blast resistance gene, Map-based cloning, NBS-LRR gene, Rice