Methodical approaches to determine the rate of radial muscle displacement using tensiomyography: A scoping review and new reporting guideline

Tensiomyography is a non-invasive method to assess skeletal muscle contractile properties from the stimulated radial displacement. Many studies have used the rate of displacement (Vc) as an indirect measure of muscle contraction velocity. However, no standardised methodical approach exists to measure displacement and determine Vc. This review aimed to provide an overview of concepts to determine Vc and measurement protocols to foster the development of a standardised methodical approach. This review followed the Preferred Reporting Items for Systematic Reviews and meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guideline. Systematic searches were performed within five electronic databases and additional sources. The included 62 studies reported 10 different concepts to determine Vc, which we summarised in three groups. The determination concepts differed mainly regarding time intervals during the contraction phase considered and criteria used to define these intervals. Essential information on the equipment and raters, measurement setup, electrical stimulation procedure, and data analysis were frequently not reported. In conclusion, no consensus on how to determine Vc existed. Incomplete reporting of measurement protocols hindered study comparison, which obstructs developing a standardised approach. Therefore, we propose a new guideline for reporting measurement protocols, which covers the 1) equipment and rater, 2) measurement setup, including positioning of the subject, sensor and electrodes, 3) electrical stimulation, including initial stimulation amplitude, increment, and endpoint, and 4) data analysis, including selection criteria and number of analysed signals and a definition of derived parameters.

The fungal root endophyte Serendipita vermifera displays inter-kingdom synergistic beneficial effects with the microbiota in Arabidopsis thaliana and barley

Plant root-associated bacteria can confer protection against pathogen infection. By contrast, the beneficial effects of root endophytic fungi and their synergistic interactions with bacteria remain poorly defined. We demonstrate that the combined action of a fungal root endophyte from a widespread taxon with core bacterial microbiota members provides synergistic protection against an aggressive soil-borne pathogen in Arabidopsis thaliana and barley. We additionally reveal early inter-kingdom growth promotion benefits which are host and microbiota composition dependent. Using RNA-sequencing, we show that these beneficial activities are not associated with extensive host transcriptional reprogramming but rather with the modulation of expression of microbial effectors and carbohydrate-active enzymes.

The Transcription Factor EIL1 Participates in the Regulation of Sulfur-Deficiency Response

Sulfur, an indispensable constituent of many cellular components, is a growth-limiting macronutrient for plants. Thus, to successfully adapt to changing sulfur availability and environmental stress, a sulfur-deficiency response helps plants to cope with the limited supply. On the transcriptional level, this response is controlled by SULFUR LIMITATION1 (SLIM1), a member of the ETHYLENE-INSENSITIVE3-LIKE (EIL) transcription factor family. In this study, we identified EIL1 as a second transcriptional activator regulating the sulfur-deficiency response, subordinate to SLIM1/EIL3. Our comprehensive RNA sequencing analysis in Arabidopsis (Arabidopsis thaliana) allowed us to obtain a complete picture of the sulfur-deficiency response and quantify the contributions of these two transcription factors. We confirmed the key role of SLIM1/EIL3 in controlling the response, particularly in the roots, but showed that in leaves more than 50% of the response is independent of SLIM1/EIL3 and EIL1. RNA sequencing showed an additive contribution of EIL1 to the regulation of the sulfur-deficiency response but also identified genes specifically regulated through EIL1. SLIM1/EIL3 seems to have further functions (e.g. in the regulation of genes responsive to hypoxia or mediating defense at both low and normal sulfur supply). These results contribute to the dissection of mechanisms of the sulfur-deficiency response and provide additional possibilities to improve adaptation to sulfur-deficiency conditions.

A secreted fungal histidine- and alanine-rich protein regulates metal ion homeostasis and oxidative stress

Like pathogens, beneficial endophytic fungi secrete effector proteins to promote plant colonization, for example, through perturbation of host immunity. The genome of the root endophyte Serendipita indica encodes a novel family of highly similar, small alanine- and histidine-rich proteins, whose functions remain unknown. Members of this protein family carry an N-terminal signal peptide and a conserved C-terminal DELD motif. Here we report on the functional characterization of the plant-responsive DELD family protein Dld1 using a combination of structural, biochemical, biophysical and cytological analyses. The crystal structure of Dld1 shows an unusual, monomeric histidine zipper consisting of two antiparallel coiled-coil helices. Similar to other histidine-rich proteins, Dld1 displays varying affinity to different transition metal ions and undergoes metal ion- and pH-dependent unfolding. Transient expression of mCherry-tagged Dld1 in barley leaf and root tissue suggests that Dld1 localizes to the plant cell wall and accumulates at cell wall appositions during fungal penetration. Moreover, recombinant Dld1 enhances barley root colonization by S. indica, and inhibits H₂ O₂ -mediated radical polymerization of 3,3'-diaminobenzidine. Our data suggest that Dld1 has the potential to enhance micronutrient accessibility for the fungus and to interfere with oxidative stress and reactive oxygen species homeostasis to facilitate host colonization.

The inconspicuous gatekeeper: endophytic Serendipita vermifera acts as extended plant protection barrier in the rhizosphere

In nature, beneficial and pathogenic fungi often simultaneously colonise plants. Despite substantial efforts to understand the composition of natural plant-microbe communities, the mechanisms driving such multipartite interactions remain largely unknown. Here we address how the interaction between the beneficial root endophyte Serendipita vermifera and the pathogen Bipolaris sorokiniana affects fungal behaviour and determines barley host responses using a gnotobiotic soil-based split-root system. Fungal confrontation in soil resulted in induction of B. sorokiniana genes involved in secondary metabolism and a significant repression of genes encoding putative effectors. In S. vermifera, genes encoding hydrolytic enzymes were strongly induced. This antagonistic response was not activated during the tripartite interaction in barley roots. Instead, we observed a specific induction of S. vermifera genes involved in detoxification and redox homeostasis. Pathogen infection but not endophyte colonisation resulted in substantial host transcriptional reprogramming and activation of defence. In the presence of S. vermifera, pathogen infection and disease symptoms were significantly reduced despite no marked alterations of the plant transcriptional response. The activation of stress response genes and concomitant repression of putative effector gene expression in B. sorokiniana during confrontation with the endophyte suggest a reduction of the pathogen's virulence potential before host plant infection.

FGB1 and WSC3 are in planta-induced β-glucan-binding fungal lectins with different functions

In the root endophyte Serendipita indica, several lectin-like members of the expanded multigene family of WSC proteins are transcriptionally induced in planta and are potentially involved in β-glucan remodeling at the fungal cell wall. Using biochemical and cytological approaches we show that one of these lectins, SiWSC3 with three WSC domains, is an integral fungal cell wall component that binds to long-chain β1-3-glucan but has no affinity for shorter β1-3- or β1-6-linked glucose oligomers. Comparative analysis with the previously identified β-glucan-binding lectin SiFGB1 demonstrated that whereas SiWSC3 does not require β1-6-linked glucose for efficient binding to branched β1-3-glucan, SiFGB1 does. In contrast to SiFGB1, the multivalent SiWSC3 lectin can efficiently agglutinate fungal cells and is additionally induced during fungus-fungus confrontation, suggesting different functions for these two β-glucan-binding lectins. Our results highlight the importance of the β-glucan cell wall component in plant-fungus interactions and the potential of β-glucan-binding lectins as specific detection tools for fungi in vivo.

Serendipita indica E5'NT modulates extracellular nucleotide levels in the plant apoplast and affects fungal colonization

Extracellular adenosine 5′‐triphosphate (eATP) is an essential signaling molecule that mediates different cellular processes through its interaction with membrane‐associated receptor proteins in animals and plants. eATP regulates plant growth, development, and responses to biotic and abiotic stresses. Its accumulation in the apoplast induces ROS production and cytoplasmic calcium increase mediating a defense response to invading microbes. We show here that perception of extracellular nucleotides, such as eATP, is important in plant–fungus interactions and that during colonization by the beneficial root endophyte Serendipita indica eATP accumulates in the apoplast at early symbiotic stages. Using liquid chromatography–tandem mass spectrometry, and cytological and functional analysis, we show that S. indica secrets SiE5′NT, an enzymatically active ecto‐5′‐nucleotidase capable of hydrolyzing nucleotides in the apoplast. Arabidopsis thaliana lines producing extracellular SiE5′NT are significantly better colonized, have reduced eATP levels, and altered responses to biotic stresses, indicating that SiE5′NT functions as a compatibility factor. Our data suggest that extracellular bioactive nucleotides and their perception play an important role in fungus–root interactions and that fungal‐derived enzymes can modify apoplastic metabolites to promote fungal accommodation.

Root-associated fungal microbiota of nonmycorrhizal Arabis alpina and its contribution to plant phosphorus nutrition

Most land plants live in association with arbuscular mycorrhizal (AM) fungi and rely on this symbiosis to scavenge phosphorus (P) from soil. The ability to establish this partnership has been lost in some plant lineages like the Brassicaceae, which raises the question of what alternative nutrition strategies such plants have to grow in P-impoverished soils. To understand the contribution of plant-microbiota interactions, we studied the root-associated fungal microbiome of Arabis alpina (Brassicaceae) with the hypothesis that some of its components can promote plant P acquisition. Using amplicon sequencing of the fungal internal transcribed spacer 2, we studied the root and rhizosphere fungal communities of A. alpina growing under natural and controlled conditions including low-P soils and identified a set of 15 fungal taxa consistently detected in its roots. This cohort included a Helotiales taxon exhibiting high abundance in roots of wild A. alpina growing in an extremely P-limited soil. Consequently, we isolated and subsequently reintroduced a specimen from this taxon into its native P-poor soil in which it improved plant growth and P uptake. The fungus exhibited mycorrhiza-like traits including colonization of the root endosphere and P transfer to the plant. Genome analysis revealed a link between its endophytic lifestyle and the expansion of its repertoire of carbohydrate-active enzymes. We report the discovery of a plant-fungus interaction facilitating the growth of a nonmycorrhizal plant under native P-limited conditions, thus uncovering a previously underestimated role of root fungal microbiota in P cycling.

Matrix metalloproteinases operate redundantly in Arabidopsis immunity against necrotrophic and biotrophic fungal pathogens

Matrix metalloproteinases (MMPs) are evolutionarily conserved and multifunctional effector molecules playing pivotal roles in development and homeostasis. In this study we explored the involvement of the five Arabidopsis thaliana At-MMPs in plant defence against microbial pathogens. Expression of At2-MMP was most responsive to inoculation with fungi and a bacterial pathogen followed by At3-MMP and At5-MMP, while At1-MMP and At4-MMP were non-responsive to these biotic stresses. Loss-of-function mutants for all tested At-MMPs displayed increased susceptibility to the necrotrophic fungus Botrytis cinerea and double mutant at2,3-mmp and triple mutant at2,3,5-mmp plants developed even stronger symptoms. Consistent with this, transgenic Arabidopsis plants that expressed At2-MMP constitutively under the Cauliflower mosaic virus 35S promoter showed enhanced resistance to the necrotrophic pathogen. Similarly, resistance to the biotrophic Arabidopsis powdery mildew fungus Golovinomyces orontii was also compromised particularly in the at2,3-mmp / at2,3,5-mmp multiplex mutants, and increased in At2-MMP overexpressor plants. The degree of disease resistance of at-mmp mutants and At2-MMP overexpressor plants also correlated positively with the degree of MAMP-triggered callose deposition in response to the bacterial flagellin peptide flg22, suggesting that matrix metalloproteinases contribute to pattern-triggered immunity (PTI) in interactions of Arabidopsis with necrotrophic and biotrophic pathogens.

The fungal-specific β-glucan-binding lectin FGB1 alters cell-wall composition and suppresses glucan-triggered immunity in plants

β-glucans are well-known modulators of the immune system in mammals but little is known about β-glucan triggered immunity in planta. Here we show by isothermal titration calorimetry, circular dichroism spectroscopy and nuclear magnetic resonance spectroscopy that the FGB1 gene from the root endophyte Piriformospora indica encodes for a secreted fungal-specific β-glucan-binding lectin with dual function. This lectin has the potential to both alter fungal cell wall composition and properties, and to efficiently suppress β-glucan-triggered immunity in different plant hosts, such as Arabidopsis, barley and Nicotiana benthamiana. Our results hint at the existence of fungal effectors that deregulate innate sensing of β-glucan in plants.

Mutualistic root endophytism is not associated with the reduction of saprotrophic traits and requires a noncompromised plant innate immunity

During a compatible interaction, the sebacinoid root-associated fungi Piriformospora indica and Sebacina vermifera induce modification of root morphology and enhance shoot growth in Arabidopsis thaliana. The genomic traits common in these two fungi were investigated and compared with those of other root-associated fungi and saprotrophs. The transcriptional responses of the two sebacinoid fungi and of Arabidopsis roots to colonization at three different symbiotic stages were analyzed by custom-designed microarrays. We identified key genomic features characteristic of sebacinoid fungi, such as expansions for gene families involved in hydrolytic activities, carbohydrate-binding and protein-protein interaction. Additionally, we show that colonization of Arabidopsis correlates with the induction of salicylic acid catabolism and accumulation of jasmonate and glucosinolates (GSLs). Genes involved in root developmental processes were specifically induced by S. vermifera at later stages during interaction. Using different Arabidopsis indole-GSLs mutants and measurement of secondary metabolites, we demonstrate the importance of the indolic glucosinolate pathway in the growth restriction of P. indica and S. vermifera and we identify indole-phytoalexins and specifically indole-carboxylic acids derivatives as potential key players in the maintenance of a mutualistic interaction with root endophytes.

Bacteria-triggered systemic immunity in barley is associated with WRKY and ETHYLENE RESPONSIVE FACTORs but not with salicylic acid

Leaf-to-leaf systemic immune signaling known as systemic acquired resistance is poorly understood in monocotyledonous plants. Here, we characterize systemic immunity in barley (Hordeum vulgare) triggered after primary leaf infection with either Pseudomonas syringae pathovar japonica (Psj) or Xanthomonas translucens pathovar cerealis (Xtc). Both pathogens induced resistance in systemic, uninfected leaves against a subsequent challenge infection with Xtc. In contrast to systemic acquired resistance in Arabidopsis (Arabidopsis thaliana), systemic immunity in barley was not associated with NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 or the local or systemic accumulation of salicylic acid. Instead, we documented a moderate local but not systemic induction of abscisic acid after infection of leaves with Psj. In contrast to salicylic acid or its functional analog benzothiadiazole, local applications of the jasmonic acid methyl ester or abscisic acid triggered systemic immunity to Xtc. RNA sequencing analysis of local and systemic transcript accumulation revealed unique gene expression changes in response to both Psj and Xtc and a clear separation of local from systemic responses. The systemic response appeared relatively modest, and quantitative reverse transcription-polymerase chain reaction associated systemic immunity with the local and systemic induction of two WRKY and two ETHYLENE RESPONSIVE FACTOR (ERF)-like transcription factors. Systemic immunity against Xtc was further associated with transcriptional changes after a secondary/systemic Xtc challenge infection; these changes were dependent on the primary treatment. Taken together, bacteria-induced systemic immunity in barley may be mediated in part by WRKY and ERF-like transcription factors, possibly facilitating transcriptional reprogramming to potentiate immunity.

Phylogenetic analysis of barley WRKY proteins and characterization of HvWRKY1 and -2 as repressors of the pathogen-inducible gene HvGER4c

The WRKY transcription factors belong to an evolutionarily conserved superprotein family predominantly present in the plant kingdom. WRKY proteins of barley are not yet fully annotated and most of them are not functionally characterized. We performed a genome-wide identification of WRKY members based on the recently accessible barley draft genome sequence and full-length cDNA datasets. As a result, 34 novel putative proteins have been identified which extend the existing list for barley WRKYs to 94. Phylogenetic analysis of the WRKY domains allowed ranking into three groups (I, II, III), with an expansion in group III in monocots. Two members of subgroup IIa, the wound and pathogen-inducible HvWRKY1 and HvWRKY2, are known as negative defense regulators. Here, we demonstrate that both transcription factors repress the activity of the powdery mildew-induced promoter of HvGER4c, a germin-like defense-related protein. The repression did not require the negative defense regulator MLO nor was it affected by the presence of the R protein MLA12. Moreover, the expression of the Arabidopsis ortholog AtWRKY40 in barley compromised basal resistance to powdery mildew, providing evidence for functional conservation of sequence-related WRKY proteins across monocots and dicots.

Broad compatibility in fungal root symbioses

Plants associate with a wide range of beneficial fungi in their roots which facilitate plant mineral nutrient uptake in exchange for carbohydrates and other organic metabolites. These associations play a key role in shaping terrestrial ecosystems and are widely believed to have promoted the evolution of land plants. To establish compatibility with their host, root-associated fungi have evolved diverse colonization strategies with distinct morphological, functional and genomic specializations as well as different degrees of interdependence. They include obligate biotrophic arbuscular mycorrhizal (AM), and facultative biotrophic ectomycorrhizal (ECM) interactions but are not restricted to these well-characterized symbioses. There is growing evidence that root endophytic associations, which due to their inconspicuous nature have been often overlooked, can be of mutualistic nature and represent important players in natural and managed environments. Recent research into the biology and genomics of root associations revealed fascinating insight into the phenotypic and trophic plasticity of these fungi and underlined genomic traits associated with biotrophy and saprotrophy. In this review we will consider the commonalities and differences of AM and ECM associations and contrast them with root endophytes.

The compromised recognition of turnip crinkle virus1 subfamily of microrchidia ATPases regulates disease resistance in barley to biotrophic and necrotrophic pathogens

MORC1 and MORC2, two of the seven members of the Arabidopsis (Arabidopsis thaliana) Compromised Recognition of Turnip Crinkle Virus1 subfamily of microrchidia Gyrase, Heat Shock Protein90, Histidine Kinase, MutL (GHKL) ATPases, were previously shown to be required in multiple layers of plant immunity. Here, we show that the barley (Hordeum vulgare) MORCs also are involved in disease resistance. Genome-wide analyses identified five MORCs that are 37% to 48% identical on the protein level to AtMORC1. Unexpectedly, and in clear contrast to Arabidopsis, RNA interference-mediated knockdown of MORC in barley resulted in enhanced basal resistance and effector-triggered, powdery mildew resistance locus A12-mediated resistance against the biotrophic powdery mildew fungus (Blumeria graminis f. sp. hordei), while MORC overexpression decreased resistance. Moreover, barley knockdown mutants also showed higher resistance to Fusarium graminearum. Barley MORCs, like their Arabidopsis homologs, contain the highly conserved GHKL ATPase and S5 domains, which identify them as members of the MORC superfamily. Like AtMORC1, barley MORC1 (HvMORC1) binds DNA and has Mn2+-dependent endonuclease activities, suggesting that the contrasting function of MORC1 homologs in barley versus Arabidopsis is not due to differences in their enzyme activities. In contrast to AtMORCs, which are involved in silencing of transposons that are largely restricted to pericentromeric regions, barley MORC mutants did not show a loss-of-transposon silencing regardless of their genomic location. Reciprocal overexpression of MORC1 homologs in barley and Arabidopsis showed that AtMORC1 and HvMORC1 could not restore each other's function. Together, these results suggest that MORC proteins function as modulators of immunity, which can act negatively (barley) or positively (Arabidopsis) dependent on the species.

Identification of suitable reference genes for real-time RT-PCR normalization in the grapevine-downy mildew pathosystem

Due to its reproducibility and sensitivity, real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) has become the method of choice for quantifying gene expression. However, the accuracy of RT-qPCR is prone to bias if proper precautions are not taken, e.g. starting with intact, non-degraded RNA, considering the PCR efficiency and using the right reference gene(s) for normalization. It has been reported that some of the well-known reference genes are differentially regulated under certain experimental conditions suggesting that there is no gene that could be used as a universal reference. This paper aims at selecting the most suitable reference gene(s) out of six putative genes to be used as normalizer(s) for quantification of gene expression in the grapevine-downy mildew interaction as well as upon induced resistance with chemical elicitors. Moreover, the paper aims at determining the optimal number of reference genes to be used in normalization, since it has been emphasized in the literature that using multiple reference genes increases accuracy. Two different software tools, geNorm and Normfinder, were used to identify the most stable reference genes in grapevine under the aforementioned conditions. The importance of the choice of adequate reference genes is highlighted by studying chitinase expression.

Endophytic life strategies decoded by genome and transcriptome analyses of the mutualistic root symbiont Piriformospora indica

Recent sequencing projects have provided deep insight into fungal lifestyle-associated genomic adaptations. Here we report on the 25 Mb genome of the mutualistic root symbiont Piriformospora indica (Sebacinales, Basidiomycota) and provide a global characterization of fungal transcriptional responses associated with the colonization of living and dead barley roots. Extensive comparative analysis of the P. indica genome with other Basidiomycota and Ascomycota fungi that have diverse lifestyle strategies identified features typically associated with both, biotrophism and saprotrophism. The tightly controlled expression of the lifestyle-associated gene sets during the onset of the symbiosis, revealed by microarray analysis, argues for a biphasic root colonization strategy of P. indica. This is supported by a cytological study that shows an early biotrophic growth followed by a cell death-associated phase. About 10% of the fungal genes induced during the biotrophic colonization encoded putative small secreted proteins (SSP), including several lectin-like proteins and members of a P. indica-specific gene family (DELD) with a conserved novel seven-amino acids motif at the C-terminus. Similar to effectors found in other filamentous organisms, the occurrence of the DELDs correlated with the presence of transposable elements in gene-poor repeat-rich regions of the genome. This is the first in depth genomic study describing a mutualistic symbiont with a biphasic lifestyle. Our findings provide a significant advance in understanding development of biotrophic plant symbionts and suggest a series of incremental shifts along the continuum from saprotrophy towards biotrophy in the evolution of mycorrhizal association from decomposer fungi.

Insect peptide metchnikowin confers on barley a selective capacity for resistance to fungal ascomycetes pathogens

The potential of metchnikowin, a 26-amino acid residue proline-rich antimicrobial peptide synthesized in the fat body of Drosophila melanogaster was explored to engineer disease resistance in barley against devastating fungal plant pathogens. The synthetic peptide caused strong in vitro growth inhibition (IC(50) value approximately 1 muM) of the pathogenic fungus Fusarium graminearum. Transgenic barley expressing the metchnikowin gene in its 52-amino acid pre-pro-peptide form under the control of the inducible mannopine synthase (mas) gene promoter from the T(i) plasmid of Agrobacterium tumefaciens displayed enhanced resistance to powdery mildew as well as Fusarium head blight and root rot. In response to these pathogens, metchnikowin accumulated in plant apoplastic space, specifying that the insect signal peptide is functional in monocotyledons. In vitro and in vivo tests revealed that the peptide is markedly effective against fungal pathogens of the phylum Ascomycota but, clearly, less active against Basidiomycota fungi. Importantly, germination of the mutualistic basidiomycete mycorrhizal fungus Piriformospora indica was affected only at concentrations beyond 50 muM. These results suggest that antifungal peptides from insects are a valuable source for crop plant improvements and their differential activities toward different phyla of fungi denote a capacity for insect peptides to be used as selective measures on specific plant diseases.

Transgenic expression of gallerimycin, a novel antifungal insect defensin from the greater wax moth Galleria mellonella, confers resistance to pathogenic fungi in tobacco

A cDNA encoding gallerimycin, a novel antifungal peptide from the greater wax moth Galleria mellonella, was isolated from a cDNA library of genes expressed during innate immune response in the caterpillars. Upon ectopic expression of gallerimycin in tobacco, using Agrobacterium tumefaciens as a vector, gallerimycin conferred resistance to the fungal pathogens Erysiphe cichoracearum and Sclerotinia minor. Quantification of gallerimycin mRNA in transgenic tobacco by real-time PCR confirmed transgenic expression under control of the inducible mannopine synthase promoter. Leaf sap and intercellular washing fluid from transgenic tobacco inhibited in vitro germination and growth of the fungal pathogens, demonstrating that gallerimycin is secreted into intercellular spaces. The feasibility of the use of gallerimycin to counteract fungal diseases in crop plants is discussed.

Macroarray expression analysis of barley susceptibility and nonhost resistance to Blumeria graminis

Different formae speciales of the grass powdery mildew fungus Blumeria graminis undergo basic-compatible or basic-incompatible (nonhost) interactions with barley. Background resistance in compatible interactions and nonhost resistance require common genetic and mechanistic elements of plant defense. To build resources for differential screening for genes that potentially distinguish a compatible from an incompatible interaction on the level of differential gene expression of the plant, we constructed eight dedicated cDNA libraries, established 13.000 expressed sequence tag (EST) sequences and designed DNA macroarrays. Using macroarrays based on cDNAs derived from epidermal peels of plants pretreated with the chemical resistance activating compound acibenzolar-S-methyl, we compared the expression of barley gene transcripts in the early host interaction with B. graminis f.sp. hordei or the nonhost pathogen B. graminis f.sp. tritici, respectively. We identified 102 spots corresponding to 94 genes on the macroarray that gave significant B. graminis-responsive signals at 12 and/or 24 h after inoculation. In independent expression analyses, we confirmed the macroarray results for 11 selected genes. Although the majority of genes showed a similar expression profile in compatible versus incompatible interactions, about 30 of the 94 genes were expressed on slightly different levels in compatible versus incompatible interactions.

Induced disease resistance and gene expression in cereals

Disease resistance strategies reduce chemical input into the environment and are therefore powerful approaches to sustainable agriculture. Induced resistance (IR) has emerged as a potential alternative, or a complementary strategy, for crop protection. IR signifies the control of pathogens and pests by prior activation of plant defence pathways. A molecular understanding of IR in cereals, including the most important global crops wheat and rice, has been largely missing. Evidence indicating that central elements of IR pathways are conserved among Di- and Monocotyledoneae has only recently been presented, although their regulation and interaction with other plant pathways may be quite divergent. We present here a synopsis of current molecular knowledge of cereal IR mechanisms.

Identification of powdery mildew-induced barley genes by cDNA-AFLP: functional assessment of an early expressed MAP kinase

Gene expression analysis by cDNA-AFLP in barley ( Hordeum vulgare L.) after powdery mildew ( Blumeria graminis f.sp. hordei , Bgh ) inoculation revealed 615 (3.7%) of 16 500 screened cDNA fragments being differentially regulated 4 and/or 12 h after inoculation. Of these transcript derived fragments (TDFs), 120 were sequenced, and for 28 out of 29 tested, induction was confirmed via RT-PCR. Most TDFs did not show any homology to sequences with known functions, others showed homology to genes involved in primary and secondary metabolism, pathogen response, redox regulation, and signal transduction. TDFs with homology to a MAP kinase ( PWMK1 ), a WRKY transcription factor, a heparanase, an immunophilin, a cytochrome P450, and a receptor-like protein kinase were isolated as full length cDNAs. Knockdown by RNA interference via biolistic delivery of sequence specific double stranded RNA to leaf segments tagged two of these genes as possible candidates being causally involved in the outcome of the barley- Bgh interaction. Knockdown of the receptor-like protein kinase and the WRKY transcription factor increased resistance to the fungus, while knockdown of PWMK1 only led to a slightly enhanced susceptibility of epidermal cells to Bgh . This suggests that the receptor-like protein kinase and the WRKY protein are candidates for negative regulators of powdery mildew resistance. Based on expression analyses, PWMK1 appears to be more generally involved in stress response.

The white barley mutant albostrians shows enhanced resistance to the biotroph Blumeria graminis f. sp. hordei

We performed cytological and molecular analyses of the interaction between the biotrophic barley powdery mildew fungus Blumeria graminis f. sp. hordei and white and green leaves of the barley albostrians mutant. The leaves have the same nuclear genotype but differ from each other in respect to plastid differentiation. White leaves showed enhanced penetration resistance to B. graminis f. sp. hordei, associated with higher epidermal H2O2 accumulation beneath the appressorial germ tubes and protein cross-linking in papillae. Very low basal salicylic acid content was found in white leaves, which further confirmed that H2O2 accumulation and penetration resistance in barley are independent of salicylic acid. Expression analysis of stress and defense-related genes, including such being involved in reactive oxygen species production and cell death regulation, revealed stronger constitutive or pathogen-induced transcript accumulation in white leaves. We discuss the data on the basis of the finding that white albostrians leaves exhibit a supersusceptible interaction phenotype with the hemibiotrophic fungus Bipolaris sorokiniana.

Bipolaris sorokiniana, a cereal pathogen of global concern: cytological and molecular approaches towards better controldouble dagger

Summary Bipolaris sorokiniana (teleomorph Cochliobolus sativus) is the causal agent of common root rot, leaf spot disease, seedling blight, head blight, and black point of wheat and barley. The fungus is one of the most serious foliar disease constraints for both crops in warmer growing areas and causes significant yield losses. High temperature and high relative humidity favour the outbreak of the disease, in particular in South Asia's intensive 'irrigated wheat-rice' production systems. In this article, we review the taxonomy and worldwide distribution, as well as strategies to counteract the disease as an emerging threat to cereal production systems. We also review the current understanding of the cytological and molecular aspects of the interaction of the fungus with its cereal hosts, which makes B. sorokiniana a model organism for studying plant defence responses to hemibiotrophic pathogens. The contrasting roles of cell death and H(2)O(2) generation in plant defence during biotrophic and necrotrophic fungal growth phases are discussed.

Expression analysis of genes induced in barley after chemical activation reveals distinct disease resistance pathways

Abstract Salicylic acid (SA) and its synthetic mimics 2,6-dichloroisonicotinic acid (DCINA) and benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH), protect barley systemically against powdery mildew (Blumeria graminis f.sp. hordei, Bgh) infection by strengthening plant defence mechanisms that result in effective papillae and host cell death. Here, we describe the differential expression of a number of newly identified barley chemically induced (BCI) genes encoding a lipoxygenase (BCI-1), a thionin (BCI-2), an acid phosphatase (BCI-3), a Ca(2+)-binding EF-hand protein (BCI-4), a serine proteinase inhibitor (BCI-7), a fatty acid desaturase (BCI-8) and several further proteins with as yet unknown function. Compared with SA, the chemicals DCINA and BTH were more potent inducers of both gene expression and resistance. Homologues of four BCI genes were detected in wheat and were also differentially regulated upon chemical activation of disease resistance. Except for BCI-4 and BCI-5 (unknown function), the genes were also induced by exogenous application of jasmonates, whereas treatments that raise endogenous jasmonates as well as wounding were less effective. The fact that BCI genes were not expressed during incompatible barley-Bgh interactions governed by gene-for-gene relationships suggests the presence of separate pathways leading to powdery mildew resistance.