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Plant Physiology Preview Published on November 2, 2007; 10.1104/pp.107.104588
OPEN ACCESS ARTICLE
Received June 25, 2007 Identification and Characterization of NBS-LRR Genes in the Model Plant Medicago truncatula
Laboratoire des Interactions Plantes Microorganismes (LIPM), UMR CNRS-INRA 442-2594, Avenue de l'Agrobiopole, 31326 Castanet Tolosan, France; Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108, USA; Department of Plant Biology; Advanced Center for Genome Technology, Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73109, USA ; Department of Plant & Soil Sciences, University of Kentucky, 230 KTRDC, Lexington, KY 40546-0236, USA; United States Department of Agriculture–Agricultural Research Service and Department of Agronomy, Iowa State University, Ames, IA 50011, USA * Corresponding author; email: steven.cannon{at}ars.usda.gov.
The NBS-LRR gene family accounts for the largest number of known disease resistance genes, and is one of the largest gene families in plant genomes. We have identified 333 non-redundant NBS-LRRs in the current M. truncatula draft genome (Mt1.0), likely representing 4-500 NBS-LRRs in the full genome, or roughly three times the number present in Arabidopsis thaliana. Although many characteristics of the gene family are similar to those described on other plant genomes, several evolutionary features are particularly pronounced in M. truncatula, including a high degree of clustering, evidence of significant numbers of ectopic translocations from clusters to other parts of the genome, a small number of more evolutionarily stable NBS-LRRs, and numerous truncations and fusions leading to novel domain compositions. The gene family clearly has had a large impact on the structure of the genome, both through ectopic translocations (potentially, a means of seeding new NBS-LRR clusters), and through two extraordinarily large superclusters. Chromosome 6 encodes approximately 34% of all TIR-NBS-LRRs, while chromosome 3 encodes approximately 40% of all CC-NBS-LRRs. Almost all atypical domain combinations are in the TIR-NBS-LRR subfamily, with many occurring within one genomic cluster. This analysis shows the gene family not only is important functionally and agronomically, but also plays a structural role in the genome.
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