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Diversity at the Mla powdery mildew resistance locus from cultivated barley reveals sites of positive selection


Seeholzer, Sabine; Tsuchimatsu, Takashi; Jordan, Tina; Bieri, Stéphane; Pajonk, Simone; Yang, Wenxiang; Jahoor, Ahmed; Shimizu, Kentaro K; Keller, Beat; Schulze-Lefert, Paul (2010). Diversity at the Mla powdery mildew resistance locus from cultivated barley reveals sites of positive selection. Molecular Plant-Microbe Interactions, 23(4):497-509.

Abstract

The Mla locus in barley (Hordeum vulgare) conditions isolate-specific immunity to the powdery mildew fungus (Blumeria graminis f. sp. hordei) and encodes intracellular coiled-coil (CC) domain, nucleotide-binding (NB) site, and leucine-rich repeat (LRR)- containing receptor proteins. Over the last decades, genetic studies in breeding material have identified a large number of functional resistance genes at the Mla locus. To study the structural and functional diversity of this locus at the molecular level, we isolated 23 candidate MLA cDNAs from barley accessions that were previously shown by genetic studies to harbor different Mla resistance specificities. Resistance activity was detected for 13 candidate MLA cDNAs in a transient gene expression assay. Sequence alignment of the deduced MLA proteins improved secondary structure predictions, revealing four additional previously overlooked LRRs. Analysis of nucleotide diversity of the candidate and validated MLA cDNAs revealed 34 sites of positive selection. Recombination/gene conversion events were frequent in the first half of the gene, but positive selection was also found when this region was excluded. The positively selected sites are all, except two, located in the LRR domain and cluster in predicted solvent-exposed residues of the repeats 7 to 15 and adjacent turns on the concave side of the predicted solenoid protein structure. This domain-restricted pattern of positively selected sites together with the length conservation of individual LRRs suggests direct binding of effectors to MLA receptors.

The Mla locus in barley (Hordeum vulgare) conditions isolate-specific immunity to the powdery mildew fungus (Blumeria graminis f. sp. hordei) and encodes intracellular coiled-coil (CC) domain, nucleotide-binding (NB) site, and leucine-rich repeat (LRR)- containing receptor proteins. Over the last decades, genetic studies in breeding material have identified a large number of functional resistance genes at the Mla locus. To study the structural and functional diversity of this locus at the molecular level, we isolated 23 candidate MLA cDNAs from barley accessions that were previously shown by genetic studies to harbor different Mla resistance specificities. Resistance activity was detected for 13 candidate MLA cDNAs in a transient gene expression assay. Sequence alignment of the deduced MLA proteins improved secondary structure predictions, revealing four additional previously overlooked LRRs. Analysis of nucleotide diversity of the candidate and validated MLA cDNAs revealed 34 sites of positive selection. Recombination/gene conversion events were frequent in the first half of the gene, but positive selection was also found when this region was excluded. The positively selected sites are all, except two, located in the LRR domain and cluster in predicted solvent-exposed residues of the repeats 7 to 15 and adjacent turns on the concave side of the predicted solenoid protein structure. This domain-restricted pattern of positively selected sites together with the length conservation of individual LRRs suggests direct binding of effectors to MLA receptors.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:08 University Research Priority Programs > Systems Biology / Functional Genomics
07 Faculty of Science > Department of Plant and Microbial Biology
Dewey Decimal Classification:570 Life sciences; biology
580 Plants (Botany)
Uncontrolled Keywords:Alleles; Amino Acid Sequence; Gene Expression Regulation, Plant; Genetic Predisposition to Disease; Genetic Variation; Hordeum, genetics/metabolism/microbiology; Phenotype; Phylogeny; Plant Diseases, genetics/immunology; Plant Proteins, genetics/metabolism; Selection, Genetic
Language:English
Date:2010
Deposited On:30 Jan 2011 10:36
Last Modified:05 Apr 2016 14:10
Publisher:American Phytopathological Society
ISSN:0894-0282
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:10.1094/MPMI-23-4-0497
PubMed ID:20192836
Permanent URL: http://doi.org/10.5167/uzh-34715

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