title: Contrasting modes of evolution acting on the complex N locus for rust resistance in flax.
abstract: Three rust resistance specificities, N, N1 and N2, map to the complex N locus of flax. We used a degenerate PCR approach, with primers directed to the nucleotide binding site (NBS) domain characteristic of many plant resistance genes, to isolate resistance gene analogs (RGAs) from flax. One RGA clone detected RFLPs co-segregating with alleles of the N locus. With this probe we isolated four related genes that occur within a 30kbp region and encode proteins with NBS and leucine-rich repeat (LRR) domains and N-terminal Toll/Interleukin-1 Receptor homology (TIR) domains. One of these four genes was identified as the N resistance gene by sequence analysis of three mutant alleles and by transgenic expression. We isolated homologous genes from two flax lines containing the N1 or N2 specificities and from flax lines carrying no N locus resistance specificities. Analysis of shared polymorphisms among this set of 18 N locus sequences revealed three groups of genes with independent lineages. Sequence exchanges have only occurred between genes within each group, but not between groups. Two of the groups contain only one sequence from each haplotype and probably represent orthologous genes. However, the third group contains two genes from each haplotype. We suggest that the re-assortment of variation by recombination/gene conversion at this locus is limited by the degree of sequence identity between genes.
authors.affiliation: CSIRO Plant Industry, Canberra ACT 2601, Australia.
authors.forename: P N
authors.initials: PN
authors.lastname: Dodds
authors.forename: G J
authors.initials: GJ
authors.lastname: Lawrence
authors.forename: J G
authors.initials: JG
authors.lastname: Ellis
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001487:Basidiomycota; D005075:Biological Evolution; D020090:Chromosome Segregation; D029721:Drosophila Proteins; D019597:Flax / Q000235:genetics* / Q000382:microbiology; D005785:Gene Conversion; D017343:Genes, Plant; D006239:Haplotypes; D007113:Immunity, Innate / Q000235:genetics; D008562:Membrane Glycoproteins / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D010935:Plant Diseases / Q000235:genetics*; D030821:Plants, Genetically Modified; D011110:Polymorphism, Genetic; D012150:Polymorphism, Restriction Fragment Length; D017434:Protein Structure, Tertiary; D012326:RNA Splicing; D011956:Receptors, Cell Surface / Q000235:genetics; D017472:Receptors, Interleukin-1 / Q000235:genetics; D011995:Recombination, Genetic; D012641:Selection, Genetic; D017386:Sequence Homology, Amino Acid; D051193:Toll-Like Receptors
chemical_list: D029721:Drosophila Proteins; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D017472:Receptors, Interleukin-1; D051193:Toll-Like Receptors