Barley Powdery Mildew Research Articles

Blumeria hordei affects volatile emission of susceptible and resistant barley plants and modifies the defense response of recipient plants.

The barley powdery mildew disease caused by the biotrophic fungus Blumeria hordei (Bh) poses enormous risks to crop production due to yield and quality losses. Plants and fungi can produce and release volatile organic compounds (VOCs) that serve as signals in plant communication and defense response to protect themselves. The present study aims to identify VOCs released by barley (Hordeum vulgare) during Bh-infection and to decipher VOC-induced disease resistance in receiver plants. VOC profiles of susceptible MLO wild type (MLO WT) and a resistant near-isogenic backcross line (mlo5) were characterized over time (one day or three days after Bh inoculation) using TD-GC/MS. Comparative analysis revealed genotype-dependent VOC profiles and significant differences in emission rates for β-caryophyllene, linalool, (Z)-3-hexenol, and methyl salicylate. Furthermore, susceptible barley plants were exposed to the complex VOC bouquet of MLO WT or mlo5 sender plants in plant-to-plant communication. We found that VOC-induced resistance in receiver plants depended on the sender genotype in a Bh susceptibility assay. Additionally, untargeted metabolomics and gene expression studies provide evidence toward an SA-dependent pathway mediating VOC-induced resistance against powdery mildew. The exogenous application of methyl salicylate resulted in the enhanced expression of the BARLEY CHEMICALLY INDUCED-4 marker gene and induced resistance in receiver plants. The findings suggest genotype-dependent alterations in barley VOC profiles during biotrophic plant-fungus interactions and show a VOC-mediated resistance that shares components with salicylic acid-related pathways. The VOC signals identified here could serve as non-invasive markers for disease progression in barley-powdery mildew interactions and as signals for resistance induction in recipient plants.

Diverse epistatic effects in barley-powdery mildew interactions localize to host chromosome hotspots

Barley Mildew locus a (Mla) encodes a multi-allelic series of nucleotide-binding leucine-rich repeat (NLR) receptors that specify recognition to diverse cereal diseases. We exploited time-course transcriptome dynamics of barley and derived immune mutants infected with the powdery mildew fungus, Blumeria hordei (Bh), to infer gene effects governed by Mla6 and two other loci significant to disease development, Blufensin1 (Bln1), and Required for Mla6 resistance3 (rar3= Sgt1 ΔKL308-309 ). Interactions of Mla6 and Bln1 resulted in diverse epistatic effects on the Bh-induced barley transcriptome, differential immunity to Pseudomonas syringae expressing the effector protease AvrPphB, and reaction to Bh. From a total of 468 barley NLRs, 115 weregrouped under different gene effect models; genes classified under these models localized to host chromosome hotspots. The corresponding Bh infection transcriptome was classified into nine co-expressed modules, linking differential expression with pathogen structures, signifying that disease is regulated by an inter-organismal network that diversifies the response.

Changes in RNase activities and in expression of two RNase genes in powdery mildew infected barley, wheat and Brachypodium distachyon leaves

AbstractChanges in RNase activities were investigated in extracts from barley near isogenic lines without or with various powdery mildew resistance genes and were compared to changes in wheat and Brachypodium distachyon leaves after powdery mildew infections. In barley, the compatible interaction with powdery mildew induced the highest increase in RNase activity as measured spectrophotometrically. The incompatible interaction that accompanied with hypersensitive reaction in Mla leaves gave less increase, whereas incompatible interactions in Mlg and mlo barley leaves without visible symptoms gave the least increase of RNase activity. In wheat, the largest RNase activity was found in leaves infected with the compatible wheat powdery mildew or wheat stem and leaf rusts. RNase activity in B. distachyon was higher than that in healthy wheat and especially barley leaves. The electrophoretic RNase enzyme activity patterns were different in barley, wheat and B. distachyon plants, but showed similar activities as determined spectrophotometrically. Barley genes encoding endonuclease 2 and ribonuclease 3-like protein X3 showed the highest expression in the compatible barley - barley powdery mildew interaction as measured by RT-qPCR. This correlated with RNase activities in leaf extracts suggesting that RNases in barley and wheat may act as susceptibility factors of powdery mildew and rust diseases.

Powdery mildew effectors AVRA1 and BEC1016 target the ER J-domain protein HvERdj3B required for immunity in barley.

The barley powdery mildew fungus, Blumeria hordei (Bh), secretes hundreds of candidate secreted effector proteins (CSEPs) to facilitate pathogen infection and colonization. One of these, CSEP0008, is directly recognized by the barley nucleotide-binding leucine-rich-repeat (NLR) receptor MLA1 and therefore is designated AVRA1. Here, we show that AVRA1 and the sequence-unrelated Bh effector BEC1016 (CSEP0491) suppress immunity in barley. We used yeast two-hybrid next-generation interaction screens (Y2H-NGIS), followed by binary Y2H and in planta protein-protein interactions studies, and identified a common barley target of AVRA1 and BEC1016, the endoplasmic reticulum (ER)-localized J-domain protein HvERdj3B. Silencing of this ER quality control (ERQC) protein increased Bh penetration. HvERdj3B is ER luminal, and we showed using split GFP that AVRA1 and BEC1016 translocate into the ER signal peptide-independently. Overexpression of the two effectors impeded trafficking of a vacuolar marker through the ER; silencing of HvERdj3B also exhibited this same cellular phenotype, coinciding with the effectors targeting this ERQC component. Together, these results suggest that the barley innate immunity, preventing Bh entry into epidermal cells, requires ERQC. Here, the J-domain protein HvERdj3B appears to be essential and can be regulated by AVRA1 and BEC1016. Plant disease resistance often occurs upon direct or indirect recognition of pathogen effectors by host NLR receptors. Previous work has shown that AVRA1 is directly recognized in the cytosol by the immune receptor MLA1. We speculate that the AVRA1 J-domain target being inside the ER, where it is inapproachable by NLRs, has forced the plant to evolve this challenging direct recognition.

Barley powdery mildew control in Western Australia and beyond

AbstractAustralia is one of the largest barley exporters in the world, with Western Australia accounting for some 40% of national production. The crop is predominantly grown in the south and south‐west of the state in winter and spring, where temperate conditions and higher rainfall levels are more suited to barley than northern and eastern regions. Between 2007 and 2013, prolonged outbreaks of barley powdery mildew (BPM) occurred. This was brought about by a combination of the extensive use of susceptible cultivars and an over‐reliance on a small number of single mode‐of‐action demethylation inhibitor fungicides, which select for mutations in the C14α‐demethylase (Cyp51A) gene. This review highlights the steps taken to reduce losses to BPM, breeding efforts to introduce resistance into cultivars and the success of pre‐breeding research to find new and durable resistance genes. We also draw comparisons with powdery mildew in Australian wheat, where similar factors are leading to substantial outbreaks.

Genome-wide association mapping for seedling and adult resistance to powdery mildew in barley

Key messageTwo new major QTL were identified for powdery mildew resistance. We confirmed that the QTL on 7HS contributed mainly to the adult-plant resistance, while another one on chromosome arm 1HS made a significant contribution to the seedling resistance.Powdery mildew (PM), caused by Blumeria hordei, can occur at all post emergent stages of barley and constantly threatens crop production. To identify more genes for effective resistance to powdery mildew for use in breeding programs, 696 barley accessions collected from different regions of the world were evaluated for PM resistance at seedling and adult growth stages in three different states of Australia. These barley accessions were genotyped using DArTSeq with over 18,000 markers for a genome-wide association study (GWAS). Using the FarmCPU model, 54 markers showed significant associations with PM resistance scored at the seedling and adult-plant stages in different states of Australia. Another 40 markers showed tentative associations (LOD > 4.0) with resistance. These markers are distributed across all seven barley chromosomes. Most of them were grouped into eleven QTL regions, coinciding with the locations of most of the reported resistance genes. Two major MTAs were identified on chromosome arms 3HS and 5HL, with one on 3HS contributing to adult plant resistance and the one on 5HL to both seedling and adult plant resistance. An MTA on 7HS contributed mainly to the adult-plant resistance, while another one on chromosome arm 1HS made a significant contribution to the seedling resistance.

Heat Pre-Treatment Modified Host and Non-Host Interactions of Powdery Mildew with Barley Brassinosteroid Mutants and Wild Types.

High temperatures associated with climate change may increase the severity of plant diseases. This study investigated the effect of heat shock treatment on host and non-host barley powdery mildew interactions using brassinosteroid (BR) mutants of barley. Brassinosteroids are plant steroid hormones, but so far little is known about their role in plant-fungal interactions. Wild type barley cultivar Bowman and its near-isogenic lines with disturbances in BR biosynthesis or signalling showed high compatibility to barley powdery mildew race A6, while cultivar Delisa and its BR-deficient mutants 522DK and 527DK were fully incompatible with this pathogen (host plant-pathogen interactions). On the other hand, Bowman and its mutants were highly resistant to wheat powdery mildew, representing non-host plant-pathogen interactions. Heat pre-treatment induced shifts in these plant-pathogen interactions towards higher susceptibility. In agreement with the more severe disease symptoms, light microscopy showed a decrease in papillae formation and hypersensitive response, characteristic of incompatible interactions, when heat pre-treatment was applied. Mutant 527DK, but not 522DK, maintained high resistance to barley powdery mildew race A6 despite heat pre-treatment. By 10 days after heat treatment and infection, a noticeable shift became apparent in the chlorophyll a fluorescence and in various leaf reflectance parameters at all genotypes.

Breeding for durable resistance against biotrophic fungal pathogens using transgenes from wheat

Breeding for resistant crops is a sustainable way to control disease and relies on the introduction of novel resistance genes. Here, we tested three strategies on how to use transgenes from wheat to achieve durable resistance against fungal pathogens in the field. First, we tested the highly effective, overexpressed single transgene Pm3e in the background of spring wheat cultivar Bobwhite in a long-term field trial over many years. Together with previous results, this revealed that transgenic wheat line Pm3e#2 conferred complete powdery mildew resistance during a total of nine field seasons without a negative impact on yield. Furthermore, overexpressed Pm3e provided resistance to powdery mildew isolates from our worldwide collection when crossed into the elite wheat cultivar Fiorina. Second, we pyramided the four overexpressed transgenes Pm3a, Pm3b, Pm3d, and Pm3f in the background of cultivar Bobwhite and showed that the pyramided line Pm3a,b,d,f was completely resistant to powdery mildew in five field seasons. Third, we performed field trials with three barley lines expressing adult plant resistance gene Lr34 from wheat during three field seasons. Line GLP8 expressed Lr34 under control of the pathogen-inducible Hv-Ger4c promoter and provided partial barley powdery mildew and leaf rust resistance in the field with small, negative effects on yield components which might need compensatory breeding. Overall, our study demonstrates and discusses three successful strategies for achieving fungal disease resistance of wheat and barley in the field using transgenes from wheat. These strategies might confer long-term resistance if applied in a sustainable way.

Identification and investigation of barley powdery mildew (Blumeria graminis f. sp. tritici) infection in winter wheat with conventional stress reactions and non-invasive biophoton emission parameters

Identification and investigation of barley powdery mildew (Blumeria graminis f. sp. tritici) infection in winter wheat with conventional stress reactions and non-invasive biophoton emission parameters

Long noncoding RNAs emerge from transposon-derived antisense sequences and may contribute to infection stage-specific transposon regulation in a fungal phytopathogen

BackgroundThe genome of the obligate biotrophic phytopathogenic barley powdery mildew fungus Blumeria hordei is inflated due to highly abundant and possibly active transposable elements (TEs). In the absence of the otherwise common repeat-induced point mutation transposon defense mechanism, noncoding RNAs could be key for regulating the activity of TEs and coding genes during the pathogenic life cycle.ResultsWe performed time-course whole-transcriptome shotgun sequencing (RNA-seq) of total RNA derived from infected barley leaf epidermis at various stages of fungal pathogenesis and observed significant transcript accumulation and time point-dependent regulation of TEs in B. hordei. Using a manually curated consensus database of 344 TEs, we discovered phased small RNAs mapping to 104 consensus transposons, suggesting that RNA interference contributes significantly to their regulation. Further, we identified 5,127 long noncoding RNAs (lncRNAs) genome-wide in B. hordei, of which 823 originated from the antisense strand of a TE. Co-expression network analysis of lncRNAs, TEs, and coding genes throughout the asexual life cycle of B. hordei points at extensive positive and negative co-regulation of lncRNAs, subsets of TEs and coding genes.ConclusionsOur work suggests that similar to mammals and plants, fungal lncRNAs support the dynamic modulation of transcript levels, including TEs, during pivotal stages of host infection. The lncRNAs may support transcriptional diversity and plasticity amid loss of coding genes in powdery mildew fungi and may give rise to novel regulatory elements and virulence peptides, thus representing key drivers of rapid evolutionary adaptation to promote pathogenicity and overcome host defense.

One stone, two birds: The barley NLR protein MLA3 recognizes the rice blast fungus effector Pwl2 in addition to its cognate effector AVRa3 from barley powdery mildew.

One stone, two birds: The barley NLR protein MLA3 recognizes the rice blast fungus effector Pwl2 in addition to its cognate effector AVRa3 from barley powdery mildew.

Barley MLA3 recognizes the host-specificity effector Pwl2 from Magnaporthe oryzae.

Plant nucleotide-binding leucine-rich repeat (NLRs) immune receptors directly or indirectly recognize pathogen-secreted effector molecules to initiate plant defense. Recognition of multiple pathogens by a single NLR is rare and usually occurs via monitoring for changes to host proteins; few characterized NLRs have been shown to recognize multiple effectors. The barley (Hordeum vulgare) NLR gene Mildew locus a (Mla) has undergone functional diversification, and the proteins encoded by different Mla alleles recognize host-adapted isolates of barley powdery mildew (Blumeria graminis f. sp. hordei [Bgh]). Here, we show that Mla3 also confers resistance to the rice blast fungus Magnaporthe oryzae in a dosage-dependent manner. Using a forward genetic screen, we discovered that the recognized effector from M. oryzae is Pathogenicity toward Weeping Lovegrass 2 (Pwl2), a host range determinant factor that prevents M. oryzae from infecting weeping lovegrass (Eragrostis curvula). Mla3 has therefore convergently evolved the capacity to recognize effectors from diverse pathogens.

Sources of Resistance to Powdery Mildew in Wild Barley (Hordeum vulgare subsp. spontaneum) Collected in Jordan, Lebanon, and Libya

Barley powdery mildew (BPM) is caused by the pathogen Blumeria hordei (Bh) and can lead to severe yield loss. Plant pathologists are looking for new sources of resistance to BPM. Barley accessions, including the wild subspecies Hordeum vulgare subsp. spontaneum (Hvs), are stored in many gene banks and are often a valuable source of economically important characteristics. The wild barley Hvs could be a valuable resistance source for BPM. The aim of the presented investigation was to detect new sources of BPM resistance in 81 accessions of Hvs collected in Jordan (46), Lebanon (24), and Libya (11). European differential isolates of BPM were used, and resistant single plant lines were selected for use from fifteen accessions from Jordan and Libya. These resistant single plant lines were tested for the presence of specific resistance genes using a differential set of Bh isolates. Hypotheses about the presence of specific resistance genes were made by comparing the reaction spectra of the tested lines with those of differential lines. After an analysis of the obtained results, it was concluded that all 31 tested single plant lines of Hvs had genes for resistance that are not represented in the barley differential set for resistance genes to Bh. Twenty-six lines of Hvs selected from accessions originated in Jordan and Libya showed resistance reactions to all isolates used. These lines will be further tested as new sources of effective resistance and used in barley prebreeding programs.

Structural polymorphisms within a common powdery mildew effector scaffold as a driver of coevolution with cereal immune receptors

In plants, host-pathogen coevolution often manifests in reciprocal, adaptive genetic changes through variations in host nucleotide-binding leucine-rich repeat immune receptors (NLRs) and virulence-promoting pathogen effectors. In grass powdery mildew (PM) fungi, an extreme expansion of a RNase-like effector family, termed RALPH, dominates the effector repertoire, with some members recognized as avirulence (AVR) effectors by cereal NLR receptors. We report the structures of the sequence-unrelated barley PM effectors AVRA6, AVRA7, and allelic AVRA10/AVRA22 variants, which are detected by highly sequence-related barley NLRs MLA6, MLA7, MLA10, and MLA22 and of wheat PM AVRPM2 detected by the unrelated wheat NLR PM2. The AVR effectors adopt a common scaffold, which is shared with the RNase T1/F1 family. We found striking variations in the number, position, and length of individual structural elements between RALPH AVRs, which is associated with a differentiation of RALPH effector subfamilies. We show that all RALPH AVRs tested have lost nuclease and synthetase activities of the RNase T1/F1 family and lack significant binding to RNA, implying that their virulence activities are associated with neo-functionalization events. Structure-guided mutagenesis identified six AVRA6 residues that are sufficient to turn a sequence-diverged member of the same RALPH subfamily into an effector specifically detected by MLA6. Similar structure-guided information for AVRA10 and AVRA22 indicates that MLA receptors detect largely distinct effector surface patches. Thus, coupling of sequence and structural polymorphisms within the RALPH scaffold of PMs facilitated escape from NLR recognition and potential acquisition of diverse virulence functions.

A dominant-negative avirulence effector of the barley powdery mildew fungus provides mechanistic insight into barley MLA immune receptor activation.

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.

A unique resistance mechanism is associated with RBgh2 barley powdery mildew adult plant resistance

Key messageGene expression at the RBgh2 locus indicates involvement in cAMP/G-protein-coupled signalling and innate immunity in barley powdery mildew adult plant resistance.Barley powdery mildew is a globally significant disease, responsible for reduced grain yield and quality. A major effect adult plant resistance gene, RBgh2, was previously found in a landrace from Azerbaijan. The atypical phenotype suggested different underlying genetic factors compared to conventional resistance genes and to investigate this, genome-wide gene expression was compared between sets of heterogeneous doubled haploids. RBgh2 resistance is recessive and induces both temporary genome-wide gene expression changes during powdery mildew infection together with constitutive changes, principally at the RBgh2 locus. Defence-related genes significantly induced included homologues of genes associated with innate immunity and pathogen recognition. Intriguingly, RBgh2 resistance does not appear to be dependent on salicylic acid signalling, a key pathway in plant resistance to biotrophs. Constitutive co-expression of resistance gene homologues was evident at the 7HS RBgh2 locus, while no expression was evident for a 6-transmembrane gene, predicted in silico to contain both G-protein- and calmodulin-binding domains. The gene was disrupted at the 5′ end, and G-protein-binding activity was suppressed. RBgh2 appears to operate through a unique mechanism that co-opts elements of innate immunity.

Estimation of Inheritance Leaf Rust, Powdery Mildew, Yield and Yield Components in Barley through Generation Means Analysis

The success of breeding program for improvement any crop depends mainly on the available background of the inheritance of the studied traits to be selected. This study was carried out during 2018/2019, 2019/2020 and 2020/2021 grown seasons at the experimental farm of Sakha Agricultural Research Station, Agricultural Research Center, Egypt to estimate the effect of genetic parameters controlling yield and yield component traits in addition severity of leaf rust and powdery mildew disease infection. Six generations (P1, P2, F1, F2, BC1 and BC2) model was used. Results indicated that, mean effect (m) was highly significant in all evaluated crosses for all studied traits. The relative importance of additive and dominance effects differed from trait to another in each cross. For epistatic components, dominance × dominance interaction effects were more effective than other components in most studied traits. Significant or/and highly significant values in desirable direction of heterosis compared to mid and better parent were obtained from most studied crosses in yield and its attribute traits, but it found over mid parents only for cross no.1 in leaf rust and crosses no. 1 and 2 in powdery mildew infection. The estimation of broad-sense heritability showed high values for studied traits and crosses, while narrow-sense heritability and genetic advance from selection ranged from low to medium in most crosses for the agronomic traits, while it ranged from low to high for leaf rust and powdery mildew infection. Finally, the results of this study recommended the barley crosses no. 4 for improve yield potential and resistant to leaf rust and cross no. 5 to improve resistance to powdery mildew, where it had high genetic advance associated with high heritability.

Site-specific analysis reveals candidate cross-kingdom small RNAs, tRNA and rRNA fragments, and signs of fungal RNA phasing in the barley-powdery mildew interaction.

The establishment of host-microbe interactions requires molecular communication between both partners, which may involve the mutual transfer of noncoding small RNAs. Previous evidence suggests that this is also true for powdery mildew disease in barley, which is caused by the fungal pathogen Blumeria hordei. However, previous studies lacked spatial resolution regarding the accumulation of small RNAs upon host infection by B. hordei. Here, we analysed site-specific small RNA repertoires in the context of the barley-B. hordei interaction. To this end, we dissected infected leaves into separate fractions representing different sites that are key to the pathogenic process: epiphytic fungal mycelium, infected plant epidermis, isolated haustoria, a vesicle-enriched fraction from infected epidermis, and extracellular vesicles. Unexpectedly, we discovered enrichment of specific 31-33-base 5'-terminal fragments of barley 5.8S ribosomal RNA in extracellular vesicles and infected epidermis, as well as particular B. hordei transfer RNA fragments in haustoria. We describe canonical small RNAs from both the plant host and the fungal pathogen that may confer cross-kingdom RNA interference activity. Interestingly, we found first evidence of phased small interfering RNAs in B. hordei, a feature usually attributed to plants, which may be associated with the posttranscriptional control of fungal coding genes, pseudogenes, and transposable elements. Our data suggest a key and possibly site-specific role for cross-kingdom RNA interference and noncoding RNA fragments in the host-pathogen communication between B. hordei and its host barley.

The Incidence of Barley (Hordeum vulgare L.) Leaf Diseases in Central Anatolia Region of Turkey in 2020

Barley (Hordeum vulgare L.) is one of the most important cereal crops that their grains are used in the malt and forage industry. Yield and quality losses occur in barley due to abiotic and biotic stress factors. Barley leaf diseases caused by fungal pathogens are common diseases leading to significant yield losses. Within the framework of environmentally-friendly integrated crop management, disease-resistant varieties should be developed together with a breeding program for sustainable agriculture. In disease resistance studies, the first and the most important step is to monitor the situation of the disease agent(s) in a region or country. For this purpose; In 2019-2020, barley leaf diseases survey in 54 barley fields was done in 5 provinces of Central Anatolia (Ankara, Eskişehir, Kırıkkale, Kırşehir, Yozgat). As a result of the surveys, the most common disease was determined as barley stripe disease (Drechslera graminea). Barley net spot disease (D. teres f. maculata, D. teres f. teres), Barley leaf spot (Rhynchosporium commune) and Barley powdery mildew (E. graminis f. sp. hordei) diseases followed in this order.

Pathogen Resistance Depending on Jacalin-Dirigent Chimeric Proteins Is Common among Poaceae but Absent in the Dicot Arabidopsis as Evidenced by Analysis of Homologous Single-Domain Proteins.

MonocotJRLs are Poaceae-specific two-domain proteins that consist of a jacalin-related lectin (JRL) and a dirigent (DIR) domain which participate in multiple developmental processes, including disease resistance. For OsJAC1, a monocotJRL from rice, it has been confirmed that constitutive expression in transgenic rice or barley plants facilitates broad-spectrum disease resistance. In this process, both domains of OsJAC1 act cooperatively, as evidenced from experiments with artificially separated JRL- or DIR-domain-containing proteins. Interestingly, these chimeric proteins did not evolve in dicotyledonous plants. Instead, proteins with a single JRL domain, multiple JRL domains or JRL domains fused to domains other than DIR domains are present. In this study, we wanted to test if the cooperative function of JRL and DIR proteins leading to pathogen resistance was conserved in the dicotyledonous plant Arabidopsis thaliana. In Arabidopsis, we identified 50 JRL and 24 DIR proteins, respectively, from which seven single-domain JRL and two single-domain DIR candidates were selected. A single-cell transient gene expression assay in barley revealed that specific combinations of the Arabidopsis JRL and DIR candidates reduced the penetration success of barley powdery mildew. Strikingly, one of these pairs, AtJAX1 and AtDIR19, is encoded by genes located next to each other on chromosome one. However, when using natural variation and analyzing Arabidopsis ecotypes that express full-length or truncated versions of AtJAX1, the presence/absence of the full-length AtJAX1 protein could not be correlated with resistance to the powdery mildew fungus Golovinomyces orontii. Furthermore, an analysis of the additional JRL and DIR candidates in a bi-fluorescence complementation assay in Nicotiana benthamiana revealed no direct interaction of these JRL/DIR pairs. Since transgenic Arabidopsis plants expressing OsJAC1-GFP also did not show increased resistance to G. orontii, it was concluded that the resistance mediated by the synergistic activities of DIR and JRL proteins is specific for members of the Poaceae, at least regarding the resistance against powdery mildew. Arabidopsis lacks the essential components of the DIR-JRL-dependent resistance pathway.