title: Genome dynamics and evolution of the Mla (powdery mildew) resistance locus in barley.
abstract: Genes that confer defense against pathogens often are clustered in the genome and evolve via diverse mechanisms. To evaluate the organization and content of a major defense gene complex in cereals, we determined the complete sequence of a 261-kb BAC contig from barley cv Morex that spans the Mla (powdery mildew) resistance locus. Among the 32 predicted genes on this contig, 15 are associated with plant defense responses; 6 of these are associated with defense responses to powdery mildew disease but function in different signaling pathways. The Mla region is organized as three gene-rich islands separated by two nested complexes of transposable elements and a 45-kb gene-poor region. A heterochromatic-like region is positioned directly proximal to Mla and is composed of a gene-poor core with 17 families of diverse tandem repeats that overlap a hypermethylated, but transcriptionally active, gene-dense island. Paleontology analysis of long terminal repeat retrotransposons indicates that the present Mla region evolved over a period of >7 million years through a variety of duplication, inversion, and transposon-insertion events. Sequence-based recombination estimates indicate that R genes positioned adjacent to nested long terminal repeat retrotransposons, such as Mla, do not favor recombination as a means of diversification. We present a model for the evolution of the Mla region that encompasses several emerging features of large cereal genomes.
authors.affiliation: Interdepartmental Genetics Program and Department of Plant Pathology, Iowa State University, Ames, IA 50011-1020, USA.
authors.forename: Fusheng
authors.initials: F
authors.lastname: Wei
authors.forename: Rod A
authors.initials: RA
authors.lastname: Wing
authors.forename: Roger P
authors.initials: RP
authors.lastname: Wise
mesh_terms: D019175:DNA Methylation; D004251:DNA Transposable Elements / Q000235:genetics; D019143:Evolution, Molecular; D005658:Fungi / Q000254:growth & development*; D015870:Gene Expression; D018745:Genome, Plant; D001467:Hordeum / Q000235:genetics* / Q000382:microbiology; D007113:Immunity, Innate / Q000235:genetics; D018598:Minisatellite Repeats / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D016254:Mutagenesis, Insertional; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics*; D018626:Retroelements / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D020080:Tandem Repeat Sequences / Q000235:genetics; D015533:Transcriptional Activation / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; C433105:MLA1 protein, Hordeum vulgare; D010940:Plant Proteins; D018626:Retroelements