A Brachypodium UDP-Glycosyltransferase Confers Root Tolerance to Deoxynivalenol and Resistance to Fusarium Infection.

Fusarium head blight (FHB) is a cereal disease caused by Fusarium graminearum, a fungus able to produce type B trichothecenes on cereals, including deoxynivalenol (DON), which is harmful for humans and animals. Resistance to FHB is quantitative, and the mechanisms underlying resistance are poorly understood. Resistance has been related to the ability to conjugate DON into a glucosylated form, deoxynivalenol-3-O-glucose (D3G), by secondary metabolism UDP-glucosyltransferases (UGTs).

Differential gene expression and metabolomic analyses of Brachypodium distachyon infected by deoxynivalenol producing and non-producing strains of Fusarium graminearum.

Background: Fusarium Head Blight (FHB) caused primarily by Fusarium graminearum (Fg) is one of the major diseases of small-grain cereals including bread wheat. This disease both reduces yields and causes quality losses due to the production of deoxynivalenol (DON), the major type B trichothecene mycotoxin. DON has been described as a virulence factor enabling efficient colonization of spikes by the fungus in wheat, but its precise role during the infection process is still elusive.

The secondary metabolism glycosyltransferases UGT73B3 and UGT73B5 are components of redox status in resistance of Arabidopsis to Pseudomonas syringae pv. tomato.

Secondary metabolism plant glycosyltransferases (UGTs) ensure conjugation of sugar moieties to secondary metabolites (SMs) and glycosylation contributes to the great diversity, reactivity and regulation of SMs. UGT73B3 and UGT73B5, two UGTs of Arabidopsis thaliana (Arabidopsis), are involved in the hypersensitive response (HR) to the avirulent bacteria Pseudomonas syringae pv. tomato (Pst-AvrRpm1), but their function in planta is unknown.

Functional characterization of two clusters of Brachypodium distachyon UDP-glycosyltransferases encoding putative deoxynivalenol detoxification genes.

Plant small-molecule UDP-glycosyltransferases (UGT) glycosylate a vast number of endogenous substances but also act in detoxification of metabolites produced by plant-pathogenic microorganisms. The ability to inactivate the Fusarium graminearum mycotoxin deoxynivalenol (DON) into DON-3-O-glucoside is crucial for resistance of cereals. We analyzed the UGT gene family of the monocot model species Brachypodium distachyon and functionally characterized two gene clusters containing putative orthologs of previously identified DON-detoxification genes from Arabidopsis thaliana and barley.

Dissecting phosphite-induced priming in Arabidopsis infected with Hyaloperonospora arabidopsidis.

Phosphite (Phi), a phloem-mobile oxyanion of phosphorous acid (H(3)PO(3)), protects plants against diseases caused by oomycetes. Its mode of action is unclear, as evidence indicates both direct antibiotic effects on pathogens as well as inhibition through enhanced plant defense responses, and its target(s) in the plants is unknown. Here, we demonstrate that the biotrophic oomycete Hyaloperonospora arabidopsidis (Hpa) exhibits an unusual biphasic dose-dependent response to Phi after inoculation of Arabidopsis (Arabidopsis thaliana), with characteristics of indirect activity at low doses (10 mm or less) and direct inhibition at high doses (50 mm or greater).

Calcium- and ROS-mediated defence responses in BY2 tobacco cells by nonpathogenic Streptomyces sp.

Aims: The early molecular events underlying the elicitation of plant defence reactions by Gram-positive bacteria are relatively unknown. In plants, calcium and reactive oxygen species are commonly involved as cellular messengers of a wide range of biotic stimuli from pathogenic to symbiotic bacteria. In the present work, we checked whether nonpathogenic Streptomyces sp.

Preformed expression of defense is a hallmark of partial resistance to rice blast fungal pathogen Magnaporthe oryzae.

Background: Partial resistance to plant pathogens is extensively used in breeding programs since it could contribute to resistance durability. Partial resistance often builds up during plant development and confers quantitative and usually broad-spectrum resistance. However, very little is known on the mechanisms underlying partial resistance.

Peroxisomal hydrogen peroxide is coupled to biotic defense responses by ISOCHORISMATE SYNTHASE1 in a daylength-related manner.

While it is well established that reactive oxygen species can induce cell death, intracellularly generated oxidative stress does not induce lesions in the Arabidopsis (Arabidopsis thaliana) photorespiratory mutant cat2 when plants are grown in short days (SD). One interpretation of this observation is that a function necessary to couple peroxisomal hydrogen peroxide (H(2)O(2))-triggered oxidative stress to cell death is only operative in long days (LD). Like lesion formation, pathogenesis-related genes and camalexin were only induced in cat2 in LD, despite less severe intracellular redox perturbation compared with SD.

The differential spatial distribution of secondary metabolites in Arabidopsis leaves reacting hypersensitively to Pseudomonas syringae pv. tomato is dependent on the oxidative burst.

Secondary metabolites (SMs) play key roles in pathogen responses, although knowledge of their precise functions is limited by insufficient characterization of their spatial response. The present study addressed this issue in Arabidopsis leaves by non-targeted and targeted metabolite profiling of Pseudomonas syringae pv. tomato (Pst-AvrRpm1) infected and adjacent uninfected leaf tissues.

Arabidopsis GLUTATHIONE REDUCTASE1 plays a crucial role in leaf responses to intracellular hydrogen peroxide and in ensuring appropriate gene expression through both salicylic acid and jasmonic acid signaling pathways.

Glutathione is a major cellular thiol that is maintained in the reduced state by glutathione reductase (GR), which is encoded by two genes in Arabidopsis (Arabidopsis thaliana; GR1 and GR2). This study addressed the role of GR1 in hydrogen peroxide (H(2)O(2)) responses through a combined genetic, transcriptomic, and redox profiling approach. To identify the potential role of changes in glutathione status in H(2)O(2) signaling, gr1 mutants, which show a constitutive increase in oxidized glutathione (GSSG), were compared with a catalase-deficient background (cat2), in which GSSG accumulation is conditionally driven by H(2)O(2).

Cytosolic NADP-dependent isocitrate dehydrogenase contributes to redox homeostasis and the regulation of pathogen responses in Arabidopsis leaves.

Cytosolic NADP-dependent isocitrate dehydrogenase (cICDH) produces 2-oxoglutarate (2-OG) and NADPH, and is encoded by a single gene in Arabidopsis thaliana. Three allelic lines carrying T-DNA insertions in this gene showed less than 10% extractable leaf ICDH activity, but only relatively small decreases in growth compared to wild-type Col0. Metabolite profiling by gas chromatography-time of flight-mass spectrometry (GC-TOF-MS) and high-performance liquid chromatography (HPLC) revealed that loss of cICDH function produced only small effects on leaf compounds involved in carbon and nitrogen assimilation.

Crosstalks between myo-inositol metabolism, programmed cell death and basal immunity in Arabidopsis.

Background: Although it is a crucial cellular process required for both normal development and to face stress conditions, the control of programmed cell death in plants is not fully understood. We previously reported the isolation of ATXR5 and ATXR6, two PCNA-binding proteins that could be involved in the regulation of cell cycle or cell death. A yeast two-hybrid screen using ATXR5 as bait captured AtIPS1, an enzyme which catalyses the committed step of myo-inositol (MI) biosynthesis.

Microbial siderophores exert a subtle role in Arabidopsis during infection by manipulating the immune response and the iron status.

Siderophores (ferric ion chelators) are secreted by organisms in response to iron deficiency. The pathogenic enterobacterium Erwinia chrysanthemi produces two siderophores, achromobactin and chrysobactin (CB), which are required for systemic dissemination in host plants. Previous studies have shown that CB is produced in planta and can trigger the up-regulation of the plant ferritin gene AtFER1.

Pathogen-responsive expression of glycosyltransferase genes UGT73B3 and UGT73B5 is necessary for resistance to Pseudomonas syringae pv tomato in Arabidopsis.

The genome sequencing of Arabidopsis (Arabidopsis thaliana) has revealed that secondary metabolism plant glycosyltransferases (UGTs) are encoded by an unexpectedly large multigenic family of 120 members. Very little is known about their actual function in planta, in particular during plant pathogen interactions. Among them, members of the group D are of particular interest since they are related to UGTs involved in stress-inducible responses in other plant species.

Plant secondary metabolism glycosyltransferases: the emerging functional analysis.

Glycosylation is a widespread modification of plant secondary metabolites. It is involved in various functions, including the regulation of hormone homeostasis, the detoxification of xenobiotics and the biosynthesis and storage of secondary compounds. In plants, these reactions are controlled by a specific subclass of the ubiquitous glycosyltransferase family.

Transcriptional co-regulation of secondary metabolism enzymes in Arabidopsis: functional and evolutionary implications.

The combined knowledge of the Arabidopsis genome and transcriptome now allows to get an integrated view of the dynamics and evolution of metabolic pathways in plants. We used publicly available sets of microarray data obtained in a wide range of different stress and developmental conditions to investigate the co-expression of genes encoding enzymes of secondary metabolism pathways, in particular indoles, phenylpropanoids, and flavonoids. We performed hierarchical clustering of gene expression profiles and found that major enzymes of each pathway display a clear and robust co-expression throughout all the conditions studied.

Vascular associated death1, a novel GRAM domain-containing protein, is a regulator of cell death and defense responses in vascular tissues.

The hypersensitive response (HR) is a programmed cell death that is commonly associated with plant disease resistance. A novel lesion mimic mutant, vad1 (for vascular associated death1), that exhibits light conditional appearance of propagative HR-like lesions along the vascular system was identified. Lesion formation is associated with expression of defense genes, production of high levels of salicylic acid (SA), and increased resistance to virulent and avirulent strains of Pseudomonas syringae pv tomato.

Real-time PCR monitoring of fungal development in Arabidopsis thaliana infected by Alternaria brassicicola and Botrytis cinerea.

Reliable methods for disease severity assessment are of crucial importance in the study of plant pathogen interactions, either for disease diagnostic on the field or to assess phenotypical differences in plants or pathogen strains. Currently, most of the assays used in fungal disease diagnostic rely on visual assessment of the symptoms, lesion diameter measurement or spore counting. However, these tests are tedious and often cannot discriminate between slightly different levels of resistance.

Over-expression of a scopoletin glucosyltransferase in Nicotiana tabacum leads to precocious lesion formation during the hypersensitive response to tobacco mosaic virus but does not affect virus resistance.

Nicotiana tabacum Togt encodes a scopoletin glucosyltransferase (UDPglucose:scopoletin O -beta-D-glucosyltrans- ferase, EC 2.4.1.

Downregulation of a pathogen-responsive tobacco UDP-Glc:phenylpropanoid glucosyltransferase reduces scopoletin glucoside accumulation, enhances oxidative stress, and weakens virus resistance.

Plant UDP-Glc:phenylpropanoid glucosyltransferases (UGTs) catalyze the transfer of Glc from UDP-Glc to numerous substrates and regulate the activity of compounds that play important roles in plant defense against pathogens. We previously characterized two tobacco salicylic acid- and pathogen-inducible UGTs (TOGTs) that act very efficiently on the hydroxycoumarin scopoletin and on hydroxycinnamic acids. To identify the physiological roles of these UGTs in plant defense, we generated TOGT-depleted tobacco plants by antisense expression.

Comparison of the expression patterns of two small gene families of S gene family receptor kinase genes during the defence response in Brassica oleracea and Arabidopsis thaliana.

SFR2, a member of the S gene family of receptor kinases, has been shown to be rapidly induced by wounding and bacterial infection suggesting that this gene may play a role in the defence response in Brassica. In this study we have compared the response of SFR2 to that of two other members of the SFR gene family in Brassica (SFR1 and SFR3) and to the closely-related ARK genes of Arabidopsis. Different patterns of mRNA accumulation were observed for different members of these families.

Free and conjugated benzoic acid in tobacco plants and cell cultures. Induced accumulation upon elicitation of defense responses and role as salicylic acid precursors.

Salicylic acid (SA) is a key endogenous component of local and systemic disease resistance in plants. In this study, we investigated the role of benzoic acid (BA) as precursor of SA biosynthesis in tobacco (Nicotiana tabacum cv Samsun NN) plants undergoing a hypersensitive response following infection with tobacco mosaic virus or in tobacco cell suspensions elicited with beta-megaspermin, an elicitor from Phytophthora megasperma. We found a small pool of conjugated BA in healthy leaves and untreated cell suspensions of tobacco, whereas free BA levels were barely detectable.

hxc2, an Arabidopsis mutant with an altered hypersensitive response to Xanthomonas campestris pv. campestris.

A chemical mutagenized population of Arabidopsis Col-0-gl plants was screened for an altered hypersensitive response (HR) after spray inoculation with an HR-inducing isolate of Xanthomonas campestris pv. campestris (strain 147). Three classes of mutant were identified: those exhibiting an HR- phenotype or partial loss of HR; hyper-responsive mutants showing necrotic lesions rapidly leading to the collapse of leaves; and susceptible mutants.

An early salicylic acid-, pathogen- and elicitor-inducible tobacco glucosyltransferase: role in compartmentalization of phenolics and H2O2 metabolism.

Treatment of tobacco cell suspension cultures with a fungal elicitor of defense responses resulted in an early accumulation of the phenylpropanoid glucosyltransferase TOGT, along with the rapid synthesis and secretion of scopolin, the glucoside of scopoletin. Elicitor-triggered extracellular accumulation of the aglycone scopoletin and of free caffeic and ferulic acids could only be revealed in the presence of diphenylene iodonium, an inhibitor of extracellular H2O2 production. Our results strongly support a role for TOGT in the elicitor-stimulated production of transportable phenylpropanoid glucosides, followed by the release of free antioxidant phenolics into the extracellular medium and subsequent H2O2 scavenging.

Two tobacco genes induced by infection, elicitor and salicylic acid encode glucosyltransferases acting on phenylpropanoids and benzoic acid derivatives, including salicylic acid.

Two tobacco genes (TOGT) with homology to glucosyltransferase genes known to be induced by salicylic acid (SA) also responded rapidly to a fungal elicitor or to an avirulent pathogen. SA, although an efficient inducer, was shown not to be essential in the signal transduction pathway regulating TOGT gene expression during the resistance response. Recombinant TOGT proteins produced in Escherichia coli exhibited low, but significant, glucosyltransferase activity towards SA, but very high activity towards hydroxycoumarins and hydroxycinnamic acids, with glucose esters being the predominant products.