Expression Pattern Analysis of Four Mlo Genes from Rose

Rose (Rosa hybrida) is one of the most economically important ornamentals worldwide. Powdery mildew (Podosphaera pannosa) is a major disease in cut and potted roses. In dicots such as arabidopsis (Arabidopsis thaliana), pea (Pisum sativum), and tomato (Solanum lycopersicum), loss-of-function mutations in mildew resistance locus o (Mlo) genes confer high levels of broad-spectrum resistance to powdery mildew. Here, we present spatiotemporal expression patterns of four Mlo genes from R. hybrida based on real-time fluorescence quantitative polymerase chain reaction (qPCR). Phylogenetically closely related R. hybrida mildew resistance locus o (RhMLO) genes showed similar or overlapping tissue specificity and analogous responsiveness to external stimuli. RhMLO1 and RhMLO2 transcriptional levels were upregulated more than 2-fold by external stimuli, especially by inoculation with powdery mildew fungus P. pannosa at early time points. This phenomenon was not found for RhMLO3 or RhMLO4. The results indicated that RhMLO1 and RhMLO2 might play important roles in rose–powdery mildew pathogen interactions. Our findings may provide useful information for the study of mechanisms of powdery mildew susceptibility in rose.

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Quantitative and Temporal Definition of the Mla Transcriptional Regulon During Barley–Powdery Mildew Interactions

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-09-10-0211 ◽

2011 ◽

Vol 24 (6) ◽

pp. 694-705 ◽

Cited By ~ 17

Author(s):

Matthew J. Moscou ◽

Nick Lauter ◽

Rico A. Caldo ◽

Dan Nettleton ◽

Roger P. Wise

Keyword(s):

Powdery Mildew ◽

Expression Profiles ◽

Coiled Coil ◽

Transcriptional Response ◽

Hypersensitive Reaction ◽

Resistance Locus ◽

Loss Of Function ◽

Transcriptional Targets ◽

Downstream Signaling ◽

Powdery Mildew Pathogen

Barley Mildew resistance locus a (Mla) is a major determinant of immunity to the powdery mildew pathogen, Blumeria graminis f. sp. hordei. Alleles of Mla encode cytoplasmic- and membrane-localized coiled-coil, nucleotide binding site, leucine-rich repeat proteins that mediate resistance when complementary avirulence effectors (AVRa) are present in the pathogen. Presence of an appropriate AVRa protein triggers nuclear relocalization of MLA, in which MLA binds repressing host transcription factors. Timecourse expression profiles of plants harboring Mla1, Mla6, and Mla12 wild-type alleles versus paired loss-of-function mutants were compared to discover conserved transcriptional targets of MLA and downstream signaling cascades. Pathogen-dependent gene expression was equivalent or stronger in susceptible plants at 20 h after inoculation (HAI) and was attenuated at later timepoints, whereas resistant plants exhibited a time-dependent strengthening of the transcriptional response, increasing in both fold change and the number of genes differentially expressed. Deregulation at 20 HAI implicated 16 HAI as a crucial point in determining the future trajectory of this interaction and was interrogated by quantitative analysis. In total, 28 potential transcriptional targets of the MLA regulon were identified. These candidate targets possess a diverse set of predicted functions, suggesting that multiple pathways are required to mediate the hypersensitive reaction.

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Chemical suppressors of mlo-mediated powdery mildew resistance

Bioscience Reports ◽

10.1042/bsr20171389 ◽

2017 ◽

Vol 37 (6) ◽

Cited By ~ 1

Author(s):

Hongpo Wu ◽

Mark Kwaaitaal ◽

Roxana Strugala ◽

Ulrich Schaffrath ◽

Paweł Bednarek ◽

...

Keyword(s):

Powdery Mildew ◽

Powdery Mildew Resistance ◽

Brefeldin A ◽

Loss Of Function ◽

Mildew Resistance ◽

Inhibitor Analysis ◽

Guanine Derivatives ◽

Powdery Mildew Pathogen ◽

Inhibitor Screen ◽

Molecular Components

Loss-of-function of barley mildew locus o (Mlo) confers durable broad-spectrum penetration resistance to the barley powdery mildew pathogen, Blumeria graminis f. sp. hordei (Bgh). Given the importance of mlo mutants in agriculture, surprisingly few molecular components have been identified to be required for this type of resistance in barley. With the aim to identify novel cellular factors contributing to mlo-based resistance, we devised a pharmacological inhibitor screen. Of the 41 rationally chosen compounds tested, five caused a partial suppression of mlo resistance in barley, indicated by increased levels of Bgh host cell entry. These chemicals comprise brefeldin A (BFA), 2′,3′-dideoxyadenosine (DDA), 2-deoxy-d-glucose, spermidine, and 1-aminobenzotriazole. Further inhibitor analysis corroborated a key role for both anterograde and retrograde endomembrane trafficking in mlo resistance. In addition, all four ribonucleosides, some ribonucleoside derivatives, two of the five nucleobases (guanine and uracil), some guanine derivatives as well as various polyamines partially suppress mlo resistance in barley via yet unknown mechanisms. Most of the chemicals identified to be effective in partially relieving mlo resistance in barley also to some extent compromised powdery mildew resistance in an Arabidopsis mlo2 mlo6 double mutant. In summary, our study identified novel suppressors of mlo resistance that may serve as valuable probes to unravel further the molecular processes underlying this unusual type of disease resistance.

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Allelic barley MLA immune receptors recognize sequence-unrelated avirulence effectors of the powdery mildew pathogen

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1612947113 ◽

2016 ◽

Vol 113 (42) ◽

pp. E6486-E6495 ◽

Cited By ~ 64

Author(s):

Xunli Lu ◽

Barbara Kracher ◽

Isabel M. L. Saur ◽

Saskia Bauer ◽

Simon R. Ellwood ◽

...

Keyword(s):

Powdery Mildew ◽

Gene Clusters ◽

Specific Cell ◽

Resistance Locus ◽

Powdery Mildew Fungus ◽

Evolutionarily Conserved ◽

Genes Encoding ◽

Barley Leaves ◽

Allele Specific ◽

Powdery Mildew Pathogen

Disease-resistance genes encoding intracellular nucleotide-binding domain and leucine-rich repeat proteins (NLRs) are key components of the plant innate immune system and typically detect the presence of isolate-specific avirulence (AVR) effectors from pathogens. NLR genes define the fastest-evolving gene family of flowering plants and are often arranged in gene clusters containing multiple paralogs, contributing to copy number and allele-specific NLR variation within a host species. Barley mildew resistance locus a (Mla) has been subject to extensive functional diversification, resulting in allelic resistance specificities each recognizing a cognate, but largely unidentified, AVRa gene of the powdery mildew fungus, Blumeria graminis f. sp. hordei (Bgh). We applied a transcriptome-wide association study among 17 Bgh isolates containing different AVRa genes and identified AVRa1 and AVRa13, encoding candidate-secreted effectors recognized by Mla1 and Mla13 alleles, respectively. Transient expression of the effector genes in barley leaves or protoplasts was sufficient to trigger Mla1 or Mla13 allele-specific cell death, a hallmark of NLR receptor-mediated immunity. AVRa1 and AVRa13 are phylogenetically unrelated, demonstrating that certain allelic MLA receptors evolved to recognize sequence-unrelated effectors. They are ancient effectors because corresponding loci are present in wheat powdery mildew. AVRA1 recognition by barley MLA1 is retained in transgenic Arabidopsis, indicating that AVRA1 directly binds MLA1 or that its recognition involves an evolutionarily conserved host target of AVRA1. Furthermore, analysis of transcriptome-wide sequence variation among the Bgh isolates provides evidence for Bgh population structure that is partially linked to geographic isolation.

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Disruption of barley immunity to powdery mildew by an in-frame Lys-Leu deletion in the essential protein SGT1

Genetics ◽

10.1093/genetics/iyaa026 ◽

2020 ◽

Vol 217 (2) ◽

Cited By ~ 1

Author(s):

Antony V E Chapman ◽

Matthew Hunt ◽

Priyanka Surana ◽

Valeria Velásquez-Zapata ◽

Weihui Xu ◽

...

Keyword(s):

Powdery Mildew ◽

Fungal Pathogens ◽

Novel Mutation ◽

Exome Capture ◽

Resistance Locus ◽

Hordeum Vulgare L ◽

Powdery Mildew Fungus ◽

Pathogen Effectors ◽

Cell Processes ◽

Disease Resistances

Abstract Barley (Hordeum vulgare L.) Mla (Mildew resistance locus a) and its nucleotide-binding, leucine-rich-repeat receptor (NLR) orthologs protect many cereal crops from diseases caused by fungal pathogens. However, large segments of the Mla pathway and its mechanisms remain unknown. To further characterize the molecular interactions required for NLR-based immunity, we used fast-neutron mutagenesis to screen for plants compromised in MLA-mediated response to the powdery mildew fungus, Blumeria graminis f. sp. hordei. One variant, m11526, contained a novel mutation, designated rar3 (required for Mla6 resistance3), that abolishes race-specific resistance conditioned by the Mla6, Mla7, and Mla12 alleles, but does not compromise immunity mediated by Mla1, Mla9, Mla10, and Mla13. This is analogous to, but unique from, the differential requirement of Mla alleles for the co-chaperone Rar1 (required for Mla12 resistance1). We used bulked-segregant-exome capture and fine mapping to delineate the causal mutation to an in-frame Lys-Leu deletion within the SGS domain of SGT1 (Suppressor of G-two allele of Skp1, Sgt1ΔKL308–309), the structural region that interacts with MLA proteins. In nature, mutations to Sgt1 usually cause lethal phenotypes, but here we pinpoint a unique modification that delineates its requirement for some disease resistances, while unaffecting others as well as normal cell processes. Moreover, the data indicate that the requirement of SGT1 for resistance signaling by NLRs can be delimited to single sites on the protein. Further study could distinguish the regions by which pathogen effectors and host proteins interact with SGT1, facilitating precise editing of effector incompatible variants.

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Diversity at the Mla Powdery Mildew Resistance Locus from Cultivated Barley Reveals Sites of Positive Selection

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-23-4-0497 ◽

2010 ◽

Vol 23 (4) ◽

pp. 497-509 ◽

Cited By ~ 102

Author(s):

Sabine Seeholzer ◽

Takashi Tsuchimatsu ◽

Tina Jordan ◽

Stéphane Bieri ◽

Simone Pajonk ◽

...

Keyword(s):

Powdery Mildew ◽

Positive Selection ◽

Transient Gene Expression ◽

Coiled Coil ◽

Resistance Locus ◽

Powdery Mildew Fungus ◽

Genetic Studies ◽

Mla Locus ◽

Or Gene ◽

Positively Selected Sites

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 LRR. Analysis of nucleotide diversity of the candidate and validated MLA cDNAs revealed 34 sites of positive selection. Recombination or 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 LRR, suggests direct binding of effectors to MLA receptors.

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Identification and mapping of PmSE5785, a new recessive powdery mildew resistance locus, in synthetic hexaploid wheat

Euphytica ◽

10.1007/s10681-015-1560-7 ◽

2015 ◽

Vol 207 (3) ◽

pp. 619-626 ◽

Cited By ~ 6

Author(s):

Yajuan Wang ◽

Changyou Wang ◽

Wei Quan ◽

Xiujuan Jia ◽

Ying Fu ◽

...

Keyword(s):

Powdery Mildew ◽

Hexaploid Wheat ◽

Powdery Mildew Resistance ◽

Synthetic Hexaploid Wheat ◽

Resistance Locus ◽

Mildew Resistance ◽

Synthetic Hexaploid

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Naturally Occurring Broad-Spectrum Powdery Mildew Resistance in a Central American Tomato Accession Is Caused by Loss of Mlo Function

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-21-1-0030 ◽

2008 ◽

Vol 21 (1) ◽

pp. 30-39 ◽

Cited By ~ 171

Author(s):

Yuling Bai ◽

Stefano Pavan ◽

Zheng Zheng ◽

Nana F. Zappel ◽

Anja Reinstädler ◽

...

Keyword(s):

Powdery Mildew ◽

Broad Spectrum ◽

Powdery Mildew Resistance ◽

Candidate Gene Approach ◽

Loss Of Function ◽

Virus Induced Gene Silencing ◽

Coding Region ◽

Oidium Neolycopersici ◽

Tomato Cultivar ◽

Mildew Resistance

The resistant cherry tomato (Solanum lycopersicum var. cerasiforme) line LC-95, derived from an accession collected in Ecuador, harbors a natural allele (ol-2) that confers broad-spectrum and recessively inherited resistance to powdery mildew (Oidium neolycopersici). As both the genetic and phytopathological characteristics of ol-2–mediated resistance are reminiscent of powdery mildew immunity conferred by loss-of-function mlo alleles in barley and Arabidopsis, we initiated a candidate-gene approach to clone Ol-2. A tomato Mlo gene (SlMlo1) with high sequence-relatedness to barley Mlo and Arabidopsis AtMLO2 mapped to the chromosomal region harboring the Ol-2 locus. Complementation experiments using transgenic tomato lines as well as virus-induced gene silencing assays suggested that loss of SlMlo1 function is responsible for powdery mildew resistance conferred by ol-2. In progeny of a cross between a resistant line bearing ol-2 and the susceptible tomato cultivar Moneymaker, a 19-bp deletion disrupting the SlMlo1 coding region cosegregated with resistance. This polymorphism results in a frameshift and, thus, a truncated nonfunctional SlMlo1 protein. Our findings reveal the second example of a natural mlo mutant that possibly arose post-domestication, suggesting that natural mlo alleles might be evolutionarily short-lived due to fitness costs related to loss of mlo function.

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Isolation of TIR and nonTIR NBS–LRR resistance gene analogues and identification of molecular markers linked to a powdery mildew resistance locus in chestnut rose (Rosa roxburghii Tratt)

Theoretical and Applied Genetics ◽

10.1007/s00122-005-0002-7 ◽

2005 ◽

Vol 111 (5) ◽

pp. 819-830 ◽

Cited By ~ 40

Author(s):

Qiang Xu ◽

Xiaopeng Wen ◽

Xiuxin Deng

Keyword(s):

Molecular Markers ◽

Powdery Mildew ◽

Resistance Gene ◽

Powdery Mildew Resistance ◽

Resistance Locus ◽

Mildew Resistance ◽

Chestnut Rose ◽

Rosa Roxburghii Tratt ◽

Rosa Roxburghii

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RMo1 Confers Blast Resistance in Barley and Is Located within the Complex of Resistance Genes Containing Mla, a Powdery Mildew Resistance Gene

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-19-1034 ◽

2006 ◽

Vol 19 (9) ◽

pp. 1034-1041 ◽

Cited By ~ 21

Author(s):

Tsuyoshi Inukai ◽

M. Isabel Vales ◽

Kiyosumi Hori ◽

Kazuhiro Sato ◽

Patrick M. Hayes

Keyword(s):

Powdery Mildew ◽

Linkage Map ◽

Resistance Gene ◽

Resistance Genes ◽

Rice Blast ◽

Powdery Mildew Resistance ◽

Blast Disease ◽

Grass Species ◽

Resistance Locus ◽

Mildew Resistance

Isolates of Magnaporthe oryzae (the causal agent of rice blast disease) can infect a range of grass species, including barley. We report that barley Hordeum vulgare cv. Baronesse and an experimental line, BCD47, show a range of resistance reactions to infection with two rice blast isolates. The complete resistance of Baronesse to the isolate Ken 54–20 is controlled by a single dominant gene, designated RMo1. RMo1 mapped to the same linkage map position on chromosome 1H as the powdery mildew resistance locus Mla and an expressed sequence tag (k04320) that corresponds to the barley gene 711N16.16. A resistance quantitative trait locus (QTL), at which Baronesse contributed the resistance allele, to the isolate Ken 53–33 also mapped at the same position as RMo1. Synteny analysis revealed that a corresponding region on rice chromosome 5 includes the bacterial blight resistance gene xa5. These results indicate that a defined region on the short arm of barley chromosome 1H, including RMo1 and Mla, harbors genes conferring qualitative and quantitative resistance to multiple pathogens. The partial resistance of BCD47 to Ken53–33 is determined by alleles at three QTL, two of which coincide with the linkage map positions of the mildew resistance genes mlo and Mlf.

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