Universität zu Köln

Bauer, Saskia, Yu, Dongli, Lawson, Aaron W., Saur, Isabel M. L., Frantzeskakis, Lamprinos ORCID: 0000-0001-8947-6934, Kracher, Barbara, Logemann, Elke ORCID: 0000-0002-0478-8072, Chai, Jijie ORCID: 0000-0001-7591-3873, Maekawa, Takaki and Schulze-Lefert, Paul (2021). The leucine-rich repeats in allelic barley MLA immune receptors define specificity towards sequence-unrelated powdery mildew avirulence effectors with a predicted common RNase-like fold. PLoS Pathog., 17 (2). SAN FRANCISCO: PUBLIC LIBRARY SCIENCE. ISSN 1553-7374

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Abstract

Author summary Barley powdery mildew caused by the fungus Blumeria graminis forma specialis hordei (Bgh) can result in annual yield losses of 15% of this cereal crop. Bgh promotes virulence in plants through the secretion of diverse effector molecules, small proteins of which a subset enters into and modifies the immune status and physiology of the host leaf. In response, the host has evolved a multitude of disease resistance genes. The Mildew locus a (Mla) resistance gene stands out because diversification in the host population has generated numerous Mla variants encoding multi-domain receptors, each of which can directly recognize an isolate-specific Bgh effector, designated as avirulence (AVR(A)) effectors. Recognition of AVR(A) effectors by MLA triggers plant immune responses, a phenomenon known as isolate-specific resistance, which invariably results in localized host cell death. Here, we identify the powdery mildew effector AVR(A6) and validate its specific interaction with its matching receptor MLA6. Furthermore, through the use of hybrid receptors constructed from MLA1 and MLA6 as well as MLA10 and MLA22 receptors, we provide insights into the specific domains and amino acid residues generally important for AVR(A) recognition by MLA receptors. We find that sequence variation in the leucine-rich repeats (LRRs) of multi-allelic MLA receptors determines specific recognition of AVR(A) effectors. These effectors are sequence-unrelated, but our analysis indicates that they may be structurally related. This data may assist in the future generation of synthetic immune receptors with pre-defined recognition specificities. Nucleotide-binding domain leucine-rich repeat-containing receptors (NLRs) in plants can detect avirulence (AVR) effectors of pathogenic microbes. The Mildew locus a (Mla) NLR gene has been shown to confer resistance against diverse fungal pathogens in cereal crops. In barley, Mla has undergone allelic diversification in the host population and confers isolate-specific immunity against the powdery mildew-causing fungal pathogen Blumeria graminis forma specialis hordei (Bgh). We previously isolated the Bgh effectors AVR(A1), AVR(A7), AVR(A9), AVR(A13), and allelic AVR(A10)/AVR(A22), which are recognized by matching MLA1, MLA7, MLA9, MLA13, MLA10 and MLA22, respectively. Here, we extend our knowledge of the Bgh effector repertoire by isolating the AVR(A6) effector, which belongs to the family of catalytically inactive RNase-Like Proteins expressed in Haustoria (RALPHs). Using structural prediction, we also identified RNase-like folds in AVR(A1), AVR(A7), AVR(A10)/AVR(A22), and AVR(A13), suggesting that allelic MLA recognition specificities could detect structurally related avirulence effectors. To better understand the mechanism underlying the recognition of effectors by MLAs, we deployed chimeric MLA1 and MLA6, as well as chimeric MLA10 and MLA22 receptors in plant co-expression assays, which showed that the recognition specificity for AVR(A1) and AVR(A6) as well as allelic AVR(A10) and AVR(A22) is largely determined by the receptors' C-terminal leucine-rich repeats (LRRs). The design of avirulence effector hybrids allowed us to identify four specific AVR(A10) and five specific AVR(A22) aa residues that are necessary to confer MLA10- and MLA22-specific recognition, respectively. This suggests that the MLA LRR mediates isolate-specific recognition of structurally related AVR(A) effectors. Thus, functional diversification of multi-allelic MLA receptors may be driven by a common structural effector scaffold, which could be facilitated by proliferation of the RALPH effector family in the pathogen genome.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Bauer, Saskia UNSPECIFIED UNSPECIFIED UNSPECIFIED Yu, Dongli UNSPECIFIED UNSPECIFIED UNSPECIFIED Lawson, Aaron W. UNSPECIFIED UNSPECIFIED UNSPECIFIED Saur, Isabel M. L. UNSPECIFIED UNSPECIFIED UNSPECIFIED Frantzeskakis, Lamprinos UNSPECIFIED orcid.org/0000-0001-8947-6934 UNSPECIFIED Kracher, Barbara UNSPECIFIED UNSPECIFIED UNSPECIFIED Logemann, Elke UNSPECIFIED orcid.org/0000-0002-0478-8072 UNSPECIFIED Chai, Jijie UNSPECIFIED orcid.org/0000-0001-7591-3873 UNSPECIFIED Maekawa, Takaki UNSPECIFIED UNSPECIFIED UNSPECIFIED Schulze-Lefert, Paul UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-590446
DOI:	10.1371/journal.ppat.1009223
Journal or Publication Title:	PLoS Pathog.
Volume:	17
Number:	2
Date:	2021
Publisher:	PUBLIC LIBRARY SCIENCE
Place of Publication:	SAN FRANCISCO
ISSN:	1553-7374
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language RESISTANCE GENES; DISEASE-RESISTANCE; CRYSTAL-STRUCTURES; BINARY VECTORS; WHEAT; PROTEINS; EVOLUTION; RAR1; TRANSFORMATION; IMPROVEMENTS Multiple languages Microbiology; Parasitology; Virology Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/59044