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Elife. 2019 Feb 19;8. pii: e44471. doi: 10.7554/eLife.44471.

Multiple pairs of allelic MLA immune receptor-powdery mildew AVRA effectors argue for a direct recognition mechanism.

Author information

1
Department of Plant Microbe Interactions, Max Planck Institute for Plant Breeding Research, Cologne, Germany.
2
Unit of Plant Molecular Cell Biology, Institute for Biology I, RWTH Aachen University, Aachen, Germany.
3
Department of Plant and Microbial Biology, University of Zurich, Zurich, Switzerland.
4
Cluster of Excellence on Plant Sciences, Düsseldorf, Germany.

Abstract

Nucleotide-binding domain and leucine-rich repeat (NLR)-containing proteins in plants and animals mediate intracellular pathogen sensing. Plant NLRs typically detect strain-specific pathogen effectors and trigger immune responses often linked to localized host cell death. The barley Mla disease resistance locus has undergone extensive functional diversification in the host population and encodes numerous allelic NLRs each detecting a matching isolate-specific avirulence effector (AVRA) of the fungal pathogen Blumeria graminis f. sp. hordei (Bgh). We report here the isolation of Bgh AVRa7, AVRa9, AVRa10, and AVRa22, which encode small secreted proteins recognized by allelic MLA7, MLA9, MLA10, and MLA22 receptors, respectively. These effectors are sequence-unrelated, except for allelic AVRa10 and AVRa22 that are co-maintained in pathogen populations in the form of a balanced polymorphism. Contrary to numerous examples of indirect recognition of bacterial effectors by plant NLRs, co-expression experiments with matching Mla-AVRa pairs indicate direct detection of the sequence-unrelated fungal effectors by MLA receptors.

KEYWORDS:

NLR receptor; avirulence effector; pathogen population; plant biology; plant innate immunity; powdery mildew

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