ORCID Profile
0000-0002-5610-1260
Current Organisation
University of Cologne
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Publisher: Public Library of Science (PLoS)
Date: 03-02-2021
DOI: 10.1371/JOURNAL.PPAT.1009223
Abstract: 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 erse fungal pathogens in cereal crops. In barley, Mla has undergone allelic ersification 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 ersification 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.
Publisher: Springer Science and Business Media LLC
Date: 02-2022
Publisher: Portland Press Ltd.
Date: 09-2022
DOI: 10.1042/EBC20210077
Abstract: Plant resistance (R) genes are members of large gene families with significant within and between species variation. It has been hypothesised that a variety of processes have shaped R gene evolution and the evolution of R gene specificity. In this review, we illustrate the main mechanisms that generate R gene ersity and provide ex les of how they can change R gene specificity. Next, we explain which evolutionary mechanisms are at play and how they determine the fate of new R gene alleles and R genes. Finally, we place this in a larger context by comparing the ersity and evolution of R gene specificity within and between species scales.
Publisher: Springer Science and Business Media LLC
Date: 08-12-2021
Publisher: eLife Sciences Publications, Ltd
Date: 19-02-2019
DOI: 10.7554/ELIFE.44471
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 ersification 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 ex les 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.
Publisher: Springer Science and Business Media LLC
Date: 22-05-2023
DOI: 10.1038/S41588-023-01402-1
Abstract: To safeguard bread wheat against pests and diseases, breeders have introduced over 200 resistance genes into its genome, thus nearly doubling the number of designated resistance genes in the wheat gene pool 1 . Isolating these genes facilitates their fast-tracking in breeding programs and incorporation into polygene stacks for more durable resistance. We cloned the stem rust resistance gene Sr43 , which was crossed into bread wheat from the wild grass Thinopyrum elongatum 2,3 . Sr43 encodes an active protein kinase fused to two domains of unknown function. The gene, which is unique to the Triticeae, appears to have arisen through a gene fusion event 6.7 to 11.6 million years ago. Transgenic expression of Sr43 in wheat conferred high levels of resistance to a wide range of isolates of the pathogen causing stem rust, highlighting the potential value of Sr43 in resistance breeding and engineering.
Publisher: Oxford University Press (OUP)
Date: 20-07-2023
DOI: 10.1093/JXB/ERAD285
Abstract: Nucleotide-binding leucine-rich repeat receptors (NLRs) recognize pathogen effectors to mediate plant disease resistance often involving host cell death. Effectors escape NLR recognition through polymorphisms, allowing the pathogen to proliferate on previously resistant host plants. The powdery mildew effector AVRA13-1 is recognized by the barley NLR MLA13 and activates host cell death. We demonstrate here that a virulent form of AVRA13, called AVRA13-V2, escapes MLA13 recognition by substituting a serine for a leucine residue at the C-terminus. Counterintuitively, this substitution in AVRA13-V2 resulted in an enhanced MLA13 association and prevented the detection of AVRA13-1 by MLA13. Therefore, AVRA13-V2 is a dominant-negative form of AVRA13 and has probably contributed to the breakdown of Mla13 resistance. Despite this dominant-negative activity, AVRA13-V2 failed to suppress host cell death mediated by the MLA13 autoactive MHD variant. Neither AVRA13-1 nor AVRA13-V2 interacted with the MLA13 autoactive variant, implying that the binding moiety in MLA13 that mediates association with AVRA13-1 is altered after receptor activation. We also show that mutations in the MLA13 coiled-coil domain, which were thought to impair Ca2+ channel activity and NLR function, instead resulted in MLA13 autoactive cell death. Our results constitute an important step to define intermediate receptor conformations during NLR activation.
Publisher: Cold Spring Harbor Laboratory
Date: 11-01-2023
DOI: 10.1101/2023.01.11.523539
Abstract: Nucleotide-binding leucine-rich repeat receptors (NLRs) recognize pathogen effectors to mediate plant disease resistance, which is often accompanied by a localized host cell death response. Effectors can escape NLR recognition through various polymorphisms, allowing the pathogen to proliferate on previously resistant host plants. The powdery mildew effector AVR A13 -1 is recognized by the barley NLR MLA13 and activates host cell death. We demonstrate here that a virulent form of AVR A13 , called AVR A13 -V2, escapes MLA13 recognition by substituting a serine for a leucine residue at the C-terminus. Counterintuitively, this substitution in AVR A13 -V2 resulted in an enhanced MLA13 association and prevented the detection of AVR A13 -1 by MLA13. Therefore, AVR A13 -V2 is a dominant-negative form of AVR A13 and has likely contributed to the breakdown of Mla13 resistance. Despite this dominant-negative activity, AVR A13 -V2 failed to suppress host cell death mediated by the MLA13 auto-active “MHD” variant. Neither AVR A13 -1 nor AVR A13 -V2 interacted with the MLA13 auto-active variant, implying that the binding moiety in MLA13 that mediates association with AVR A13 -1 is altered after receptor activation. We also show that mutations in the MLA13 coiled-coil signalling domain, which were thought to impair Ca 2+ -channel activity and NLR function, instead resulted in MLA13 auto-active cell death. The data constitute an important step to define intermediate receptor conformations during NLR activation.
Publisher: Springer Science and Business Media LLC
Date: 24-10-2019
DOI: 10.1186/S13007-019-0502-0
Abstract: Plant disease resistance to host-adapted pathogens is often mediated by host nucleotide-binding and leucine-rich repeat (NLR) receptors that detect matching pathogen avirulence effectors (AVR) inside plant cells. AVR-triggered NLR activation is typically associated with a rapid host cell death at sites of attempted infection and this response constitutes a widely used surrogate for NLR activation. However, it is challenging to assess this cell death in cereal hosts. Here we quantify cell death upon NLR-mediated recognition of fungal pathogen AVRs in mesophyll leaf protoplasts of barley and wheat. We provide measurements for the recognition of the fungal AVRs AvrSr50 and AVR a1 by their respective cereal NLRs Sr50 and Mla1 upon overexpression of the AVR and NLR pairs in mesophyll protoplast of both, wheat and barley. Our data demonstrate that the here described approach can be effectively used to detect and quantify death of wheat and barley cells induced by overexpression of NLR and AVR effectors or AVR effector candidate genes from erse fungal pathogens within 24 h.
Publisher: Wiley
Date: 23-02-2022
DOI: 10.1111/NPH.18011
Abstract: Pathogen effectors are crucial players during plant colonisation and infection. Plant resistance mostly relies on effector recognition to activate defence responses. Understanding how effector proteins escape from plant surveillance is important for plant breeding and resistance deployment. Here we examined the role of genetic ersity of the stem rust ( Puccinia graminis f. sp. tritici ( Pgt )) AvrSr50 gene in determining recognition by the corresponding wheat Sr50 resistance gene. We solved the crystal structure of a natural variant of AvrSr50 and used site‐directed mutagenesis and transient expression assays to dissect the molecular mechanisms explaining gain of virulence. We report that AvrSr50 can escape recognition by Sr50 through different mechanisms including DNA insertion, stop codon loss or by amino‐acid variation involving a single substitution of the AvrSr50 surface‐exposed residue Q121. We also report structural homology of AvrSr50 to cupin superfamily members and carbohydrate‐binding modules indicating a potential role in binding sugar moieties. This study identifies key polymorphic sites present in AvrSr50 alleles from natural stem rust populations that play important roles to escape from Sr50 recognition. This constitutes an important step to better understand Pgt effector evolution and to monitor AvrSr50 variants in natural rust populations.
Publisher: Elsevier BV
Date: 08-2014
DOI: 10.1016/J.PBI.2014.04.002
Abstract: One important model for disease resistance is the Prf recognition complex of tomato, which responds to different bacterial effectors. Prf incorporates a protein kinase called Pto as its recognition domain that mimics effector virulence targets, and activates resistance after interaction with specific effectors. Recent findings show that this complex is oligomeric, and reveal how this impacts mechanism. Oligomerisation brings two or more kinases into proximity, where they can phosphorylate each other after effector perception. Effector attack on one kinase activates another in trans, constituting a molecular trap for the effector. Oligomerisation of plant resistance proteins may be a general concept that broadens pathogen recognition and restricts the ability of pathogens to evolve virulence.
Publisher: eLife Sciences Publications, Ltd
Date: 11-02-2019
Publisher: Cold Spring Harbor Laboratory
Date: 13-04-2023
DOI: 10.1101/2023.04.12.536646
Abstract: Cell walls are important interfaces of plant-fungal interactions. Host cell walls act as robust physical and chemical barriers against fungal invaders, making them an essential line of defense. Upon fungal colonization, plants deposit phenolics and callose at the sites of fungal penetration to reinforce their walls and prevent further fungal progression. Alterations in the composition of plant cell walls significantly impact host susceptibility. Furthermore, plants and fungi secrete glycan hydrolases acting on each other's cell walls. These enzymes release a wide range of sugar oligomers into the apoplast, some of which trigger the activation of host immunity via host surface receptors. Recent characterization of cell walls from plant-colonizing fungi have emphasized the abundance of β-glucans in different cell wall layers, which makes them suitable targets for recognition. To characterize host components involved in immunity against fungi, we performed a protein pull-down with the biotinylated β-glucan laminarin. Thereby, we identified a glycoside hydrolase family 81-type glucan-binding protein (GBP) as the major β-glucan interactor. Mutation of GBP1 and its only paralogue GBP2 in barley led to decreased colonization by the beneficial root endophytes Serendipita indica and S. vermifera, as well as the arbuscular mycorrhizal fungus Rhizophagus irregularis. The reduction of symbiotic colonization was accompanied by enhanced responses at the host cell wall. Moreover, GBP mutation in barley also increased resistance to fungal infections in roots and leaves by the hemibiotrophic pathogen Bipolaris sorokiniana and the obligate biotrophic pathogen Blumeria graminis f. sp. hordei, respectively. These results indicate that GBP1 is involved in the establishment of symbiotic associations with beneficial fungi, a role that has potentially been appropriated by barley-adapted pathogens.
Location: Australia
No related grants have been discovered for Isabel ML Saur.