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GrainGenes Reference Report: PLC-14-1903

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Reference	PLC-14-1903
Title	Genome dynamics and evolution of the Mla (powdery mildew) resistance locus in barley
Journal	Plant Cell
Year	2002
Volume	14
Pages	1903-1917
Author	Wei FS Wong RA Wise RP
Abstract	Summary: 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
External Databases	Pubmed: 12172030
Keyword	[ Hide all but 1 of 57 ] afa-family bac bac contig barley caenorhabditis elegans cereal genomes complete sequence complexes contig core defense defense response defense responses disease disease resistance diversification dna sequence duplication dynamics element elements events evolution f-sp hordei family features gene gene complex inversion island islands locus long terminal repeat maize genome mildew model molecular characterization organization overlap plant defense plant defense response powdery mildew proteinase inhibitor-i r gene r genes r-genes recombination resistance responses retrotransposon sequence signaling signaling pathways span tandem tandem repeat transposable element

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