The Cuticle Mutant eca2 Modifies Plant Defense Responses to Biotrophic and Necrotrophic Pathogens and Herbivory Insects.

We isolated previously several Arabidopsis thaliana mutants with constitutive expression of the early microbe-associated molecular pattern-induced gene ATL2, named eca (expresión constitutiva de ATL2). Here, we further explored the interaction of eca mutants with pest and pathogens. Of all eca mutants, eca2 was more resistant to a fungal pathogen (Botrytis cinerea) and a bacterial pathogen (Pseudomonas syringae) as well as to a generalist herbivorous insect (Spodoptera littoralis). Permeability of the cuticle is increased in eca2; chemical characterization shows that eca2 has a significant reduction of both cuticular wax and cutin. Additionally, we determined that eca2 did not display a similar compensatory transcriptional response, compared with a previously characterized cuticular mutant, and that resistance to B. cinerea is mediated by the priming of the early and late induced defense responses, including salicylic acid- and jasmonic acid-induced genes. These results suggest that ECA2-dependent responses are involved in the nonhost defense mechanism against biotrophic and necrotrophic pathogens and against a generalist insect by modulation and priming of innate immunity and late defense responses. Making eca2 an interesting model to characterize the molecular basis for plant defenses against different biotic interactions and to study the initial events that take place in the cuticle surface of the aerial organs.

The Innate Immune Signaling System as a Regulator of Disease Resistance and Induced Systemic Resistance Activity Against Verticillium dahliae.

In the last decades, the plant innate immune responses against pathogens have been extensively studied, while biocontrol interactions between soilborne fungal pathogens and their hosts have received much less attention. Treatment of Arabidopsis thaliana with the nonpathogenic bacterium Paenibacillus alvei K165 was shown previously to protect against Verticillium dahliae by triggering induced systemic resistance (ISR). In the present study, we evaluated the involvement of the innate immune response in the K165-mediated protection of Arabidopsis against V. dahliae. Tests with Arabidopsis mutants impaired in several regulators of the early steps of the innate immune responses, including fls2, efr-1, bak1-4, mpk3, mpk6, wrky22, and wrky29 showed that FLS2 and WRKY22 have a central role in the K165-triggered ISR, while EFR1, MPK3, and MPK6 are possible susceptibility factors for V. dahliae and bak1 shows a tolerance phenomenon. The resistance induced by strain K165 is dependent on both salicylate and jasmonate-dependent defense pathways, as evidenced by an increased transient accumulation of PR1 and PDF1.2 transcripts in the aerial parts of infected plants treated with strain K165.

The microbiome of the leaf surface of Arabidopsis protects against a fungal pathogen.

We have explored the importance of the phyllosphere microbiome in plant resistance in the cuticle mutants bdg (BODYGUARD) or lacs2.3 (LONG CHAIN FATTY ACID SYNTHASE 2) that are strongly resistant to the fungal pathogen Botrytis cinerea. The study includes infection of plants under sterile conditions, 16S ribosomal DNA sequencing of the phyllosphere microbiome, and isolation and high coverage sequencing of bacteria from the phyllosphere. When inoculated under sterile conditions bdg became as susceptible as wild-type (WT) plants whereas lacs2.3 mutants retained the resistance. Adding washes of its phyllosphere microbiome could restore the resistance of bdg mutants, whereas the resistance of lacs2.3 results from endogenous mechanisms. The phyllosphere microbiome showed distinct populations in WT plants compared to cuticle mutants. One species identified as Pseudomonas sp isolated from the microbiome of bdg provided resistance to B. cinerea on Arabidopsis thaliana as well as on apple fruits. No direct activity was observed against B. cinerea and the action of the bacterium required the plant. Thus, microbes present on the plant surface contribute to the resistance to B. cinerea. These results open new perspectives on the function of the leaf microbiome in the protection of plants.

Localization and expression of EDS5H a homologue of the SA transporter EDS5.

BACKGROUND: An important signal transduction pathway in plant defence depends on the accumulation of salicylic acid (SA). SA is produced in chloroplasts and the multidrug and toxin extrusion transporter ENHANCED DISEASE SUSCEPTIBILITY5 (EDS5; At4g39030) is necessary for the accumulation of SA after pathogen and abiotic stress. EDS5 is localized at the chloroplast and functions in transporting SA from the chloroplast to the cytoplasm. EDS5 has a homologue called EDS5H (EDS5 HOMOLOGUE; At2g21340) but its relationship to EDS5 has not been described and its function is not known. RESULTS: EDS5H exhibits about 72% similarity and 59% identity to EDS5. In contrast to EDS5 that is induced after pathogen inoculation, EDS5H was constitutively expressed in all green tissues, independently of pathogen infection. Both transporters are located at the envelope of the chloroplast, the compartment of SA biosynthesis. EDS5H is not involved with the accumulation of SA after inoculation with a pathogen or exposure to UV stress. A phylogenetic analysis supports the hypothesis that EDS5H may be an H(+)/organic acid antiporter like EDS5. CONCLUSIONS: The data based on genetic and molecular studies indicate that EDS5H despite its homology to EDS5 does not contribute to pathogen-induced SA accumulation like EDS5. EDS5H most likely transports related substances such as for example phenolic acids, but unlikely SA.

Export of salicylic acid from the chloroplast requires the multidrug and toxin extrusion-like transporter EDS5.

Salicylic acid (SA) is central for the defense of plants to pathogens and abiotic stress. SA is synthesized in chloroplasts from chorismic acid by an isochorismate synthase (ICS1); SA biosynthesis is negatively regulated by autoinhibitory feedback at ICS1. Genetic studies indicated that the multidrug and toxin extrusion transporter ENHANCED DISEASE SUSCEPTIBILITY5 (EDS5) of Arabidopsis (Arabidopsis thaliana) is necessary for SA accumulation after biotic and abiotic stress, but so far it is not understood how EDS5 controls the biosynthesis of SA. Here, we show that EDS5 colocalizes with a marker of the chloroplast envelope and that EDS5 functions as a multidrug and toxin extrusion-like transporter in the export of SA from the chloroplast to the cytoplasm in Arabidopsis, where it controls the innate immune response. The location at the chloroplast envelope supports a model of the effect of EDS5 on SA biosynthesis: in the eds5 mutant, stress-induced SA is trapped in the chloroplast and inhibits its own accumulation by autoinhibitory feedback.

A member of the PLEIOTROPIC DRUG RESISTANCE family of ATP binding cassette transporters is required for the formation of a functional cuticle in Arabidopsis.

Although the multilayered structure of the plant cuticle was discovered many years ago, the molecular basis of its formation and the functional relevance of the layers are not understood. Here, we present the permeable cuticle1 (pec1) mutant of Arabidopsis thaliana, which displays features associated with a highly permeable cuticle in several organs. In pec1 flowers, typical cutin monomers, such as ω-hydroxylated fatty acids and 10,16-dihydroxypalmitate, are reduced to 40% of wild-type levels and are accompanied by the appearance of lipidic inclusions within the epidermal cell. The cuticular layer of the cell wall, rather than the cuticle proper, is structurally altered in pec1 petals. Therefore, a significant role for the formation of the diffusion barrier in petals can be attributed to this layer. Thus, pec1 defines a new class of mutants. The phenotypes of the pec1 mutant are caused by the knockout of ATP BINDING CASSETTEG32 (ABCG32), an ABC transporter from the PLEIOTROPIC DRUG RESISTANCE family that is localized at the plasma membrane of epidermal cells in a polar manner toward the surface of the organs. Our results suggest that ABCG32 is involved in the formation of the cuticular layer of the cell wall, most likely by exporting particular cutin precursors from the epidermal cell.

Production of reactive oxygen species and wound-induced resistance in Arabidopsis thaliana against Botrytis cinerea are preceded and depend on a burst of calcium.

BACKGROUND: Wounded leaves of Arabidopsis thaliana produce reactive oxygen species (ROS) within minutes after wounding and become resistant to the pathogenic fungus Botrytis cinerea at a local level. This fast response of the plants to the wound is called wound-induced resistance (WIR). However the molecular mechanisms of this response and the signal cascade between the wound and ROS production are still largely unknown. Calcium is a conserved signal and it is involved in many abiotic stress responses in plants, furthermore, calcium pathways act very fast. RESULTS: The results of this study show that leaves treated with calcium channels inhibitors (verapamil) or calcium chelators (oxalate and EGTA) are impaired in ROS production. Moreover, leaves treated with verapamil, EGTA or oxalate were more susceptible to B. cinerea after wounding. The intracellular measurements of calcium changes indicated quick but transient calcium dynamics taking place few seconds after wounding in cells neighbouring the wound site. This change in the cytosolic calcium was followed in the same region by a more stable ROS burst. CONCLUSIONS: These data further extend our knowledge on the connection between wounding, calcium influx and ROS production. Moreover they provide for the first time the evidence that, following wounding, calcium changes precede a burst in ROS in the same location.

Perception of soft mechanical stress in Arabidopsis leaves activates disease resistance.

BACKGROUND: In a previous study we have shown that wounding of Arabidopsis thaliana leaves induces a strong and transient immunity to Botrytis cinerea, the causal agent of grey mould. Reactive oxygen species (ROS) are formed within minutes after wounding and are required for wound-induced resistance to B. cinerea. RESULTS: In this study, we have further explored ROS and resistance to B. cinerea in leaves of A. thaliana exposed to a soft form of mechanical stimulation without overt tissue damage. After gentle mechanical sweeping of leaf surfaces, a strong resistance to B. cinerea was observed. This was preceded by a rapid change in calcium concentration and a release of ROS, accompanied by changes in cuticle permeability, induction of the expression of genes typically associated with mechanical stress and release of biologically active diffusates from the surface. This reaction to soft mechanical stress (SMS) was fully independent of jasmonate (JA signaling). In addition, leaves exposed soft mechanical stress released a biologically active product capable of inducing resistance to B. cinerea in wild type control leaves. CONCLUSION: Arabidopsis can detect and convert gentle forms of mechanical stimulation into a strong activation of defense against the virulent fungus B. cinerea.

A permeable cuticle is associated with the release of reactive oxygen species and induction of innate immunity.

Wounded leaves of Arabidopsis thaliana show transient immunity to Botrytis cinerea, the causal agent of grey mould. Using a fluorescent probe, histological staining and a luminol assay, we now show that reactive oxygen species (ROS), including H(2)O(2) and O(2) (-), are produced within minutes after wounding. ROS are formed in the absence of the enzymes Atrboh D and F and can be prevented by diphenylene iodonium (DPI) or catalase. H(2)O(2) was shown to protect plants upon exogenous application. ROS accumulation and resistance to B. cinerea were abolished when wounded leaves were incubated under dry conditions, an effect that was found to depend on abscisic acid (ABA). Accordingly, ABA biosynthesis mutants (aba2 and aba3) were still fully resistant under dry conditions even without wounding. Under dry conditions, wounded plants contained higher ABA levels and displayed enhanced expression of ABA-dependent and ABA-reporter genes. Mutants impaired in cutin synthesis such as bdg and lacs2.3 are already known to display a high level of resistance to B. cinerea and were found to produce ROS even when leaves were not wounded. An increased permeability of the cuticle and enhanced ROS production were detected in aba2 and aba3 mutants as described for bdg and lacs2.3. Moreover, leaf surfaces treated with cutinase produced ROS and became more protected to B. cinerea. Thus, increased permeability of the cuticle is strongly linked with ROS formation and resistance to B. cinerea. The amount of oxalic acid, an inhibitor of ROS secreted by B. cinerea could be reduced using plants over expressing a fungal oxalate decarboxylase of Trametes versicolor. Infection of such plants resulted in a faster ROS accumulation and resistance to B. cinerea than that observed in untransformed controls, demonstrating the importance of fungal suppression of ROS formation by oxalic acid. Thus, changes in the diffusive properties of the cuticle are linked with the induction ROS and attending innate defenses.

Pathogen and Circadian Controlled 1 (PCC1) regulates polar lipid content, ABA-related responses, and pathogen defence in Arabidopsis thaliana.

Pathogen and Circadian Controlled 1 (PCC1) was previously characterized as a regulator of defence against pathogens and stress-activated transition to flowering. Plants expressing an RNA interference construct for the PCC1 gene (iPCC1 plants) showed a pleiotropic phenotype. They were hypersensitive to abscisic acid (ABA) as shown by reduced germination potential and seedling establishment, as well as reduced stomatal aperture and main root length in ABA-supplemented media. In addition, iPCC1 plants displayed alterations in polar lipid contents and their corresponding fatty acids. Importantly, a significant reduction in the content of phosphatidylinositol (PI) was observed in iPCC1 leaves when compared with wild-type plants. A trend in reduced levels of 18:0 and increased levels of 18:2 and particularly 18:3 was also detected in several classes of polar lipids. The enhanced ABA-mediated responses and the reduced content of PI might be responsible for iPCC1 plants displaying a complex pattern of defence against pathogens of different lifestyles. iPCC1 plants were more susceptible to the hemi-biotrophic oomycete pathogen Phytophthora brassicae and more resistant to the necrotrophic fungal pathogen Botrytis cinerea compared with wild-type plants.

Pathogen stress increases somatic recombination frequency in Arabidopsis.

Evolution is based on genetic variability and subsequent phenotypic selection. Mechanisms that modulate the rate of mutation according to environmental cues, and thus control the balance between genetic stability and flexibility, might provide a distinct evolutionary advantage. Stress-induced mutations stimulated by unfavorable environments, and possible mechanisms for their induction, have been described for several organisms, but research in this area has mainly focused on microorganisms. We have analyzed the influence of adverse environmental conditions on the genetic stability of the higher plant Arabidopsis thaliana. Here we show that a biotic stress factor-attack by the oomycete pathogen Peronospora parasitica-can stimulate somatic recombination in Arabidopsis. The same effect was observed when plant pathogen-defense mechanisms were activated by the chemicals 2,6-dichloroisonicotinic acid (INA) or benzothiadiazole (BTH), or by a mutation (cim3). Together with previous studies of recombination induced by abiotic factors, these findings suggest that increased somatic recombination is a general stress response in plants. The increased genetic flexibility might facilitate evolutionary adaptation of plant populations to stressful environments.

The glutaredoxin ATGRXS13 is required to facilitate Botrytis cinerea infection of Arabidopsis thaliana plants.

Botrytis cinerea is a major pre- and post-harvest necrotrophic pathogen with a broad host range that causes substantial crop losses. The plant hormone jasmonic acid (JA) is involved in the basal resistance against this fungus. Despite basal resistance, virulent strains of B. cinerea can cause disease on Arabidopsis thaliana and virulent pathogens can interfere with the metabolism of the host in a way to facilitate infection of the plant. However, plant genes that are required by the pathogen for infection remain poorly described. To find such genes, we have compared the changes in gene expression induced in A. thaliana by JA with those induced after B. cinerea using genome-wide microarrays. We have identified genes that are repressed by JA but that are induced by B. cinerea. In this study, we describe one candidate gene, ATGRXS13, that encodes for a putative glutaredoxin and that exhibits such a crossed expression. In plants that are infected by this necrotrophic fungus, ATGRXS13 expression was negatively controlled by JA and TGA transcription factors but also through a JA-salicylic acid (SA) cross-talk mechanism as B. cinerea induced SA production that positively controlled ATGRXS13 expression. Furthermore, plants impaired in ATGRXS13 exhibited resistance to B. cinerea. Finally, we present a model whereby B. cinerea takes advantage of defence signalling pathways of the plant to help the colonization of its host.

MAP kinase phosphatase1 and protein tyrosine phosphatase1 are repressors of salicylic acid synthesis and SNC1-mediated responses in Arabidopsis.

Mitogen-activated protein (MAP) kinase phosphatases are important negative regulators of the levels and kinetics of MAP kinase activation that modulate cellular responses. The dual-specificity phosphatase MAP KINASE PHOSPHATASE1 (MKP1) was previously shown to regulate MAP KINASE6 (MPK6) activation levels and abiotic stress responses in Arabidopsis thaliana. Here, we report that the mkp1 null mutation in the Columbia (Col) accession results in growth defects and constitutive biotic defense responses, including elevated levels of salicylic acid, camalexin, PR gene expression, and resistance to the bacterial pathogen Pseudomonas syringae. PROTEIN TYROSINE PHOSPHATASE1 (PTP1) also interacts with MPK6, but the ptp1 null mutant shows no aberrant growth phenotype. However, the pronounced constitutive defense response of the mkp1 ptp1 double mutant reveals that MKP1 and PTP1 repress defense responses in a coordinated fashion. Moreover, mutations in MPK3 and MPK6 distinctly suppress mkp1 and mkp1 ptp1 phenotypes, indicating that MKP1 and PTP1 act as repressors of inappropriate MPK3/MPK6-dependent stress signaling. Finally, we provide evidence that the natural modifier of mkp1 in Col is largely the disease resistance gene homolog SUPPRESSOR OF npr1-1, CONSTITUTIVE 1 (SNC1) that is absent in the Wassilewskija accession. Our data thus indicate a major role of MKP1 and PTP1 in repressing salicylic acid biosynthesis in the autoimmune-like response caused by SNC1.

Insect eggs suppress plant defence against chewing herbivores.

Plants activate direct and indirect defences in response to insect egg deposition. However, whether eggs can manipulate plant defence is unknown. In Arabidopsis thaliana, oviposition by the butterfly Pieris brassicae triggers cellular and molecular changes that are similar to the changes caused by biotrophic pathogens. In the present study, we found that the plant defence signal salicylic acid (SA) accumulates at the site of oviposition. This is unexpected, as the SA pathway controls defence against fungal and bacterial pathogens and negatively interacts with the jasmonic acid (JA) pathway, which is crucial for the defence against herbivores. Application of P. brassicae or Spodoptera littoralis egg extract onto leaves reduced the induction of insect-responsive genes after challenge with caterpillars, suggesting that egg-derived elicitors suppress plant defence. Consequently, larval growth of the generalist herbivore S. littoralis, but not of the specialist P. brassicae, was significantly higher on plants treated with egg extract than on control plants. In contrast, suppression of gene induction and enhanced S. littoralis performance were not seen in the SA-deficient mutant sid2-1, indicating that it is SA that mediates this phenomenon. These data reveal an intriguing facet of the cross-talk between SA and JA signalling pathways, and suggest that insects have evolved a way to suppress the induction of defence genes by laying eggs that release elicitors. We show here that egg-induced SA accumulation negatively interferes with the JA pathway, and provides an advantage for generalist herbivores.

Arabidopsis thaliana class-II TGA transcription factors are essential activators of jasmonic acid/ethylene-induced defense responses.

The three closely related Arabidopsis basic leucine zipper (bZIP) transcription factors TGA2, TGA5 and TGA6 are required for the establishment of the salicylic acid (SA)-dependent plant defense response systemic acquired resistance, which is effective against biotrophic pathogens. Here we show that the same transcription factors are essential for the activation of jasmonic acid (JA)- and ethylene (ET)-dependent defense mechanisms that counteract necrotrophic pathogens: the tga256 triple mutant is impaired in JA/ET-induced PDF1.2 and b-CHI expression, which correlates with a higher susceptibility against the necrotroph Botrytis cinerea. JA/ET induction of the trans-activators ERF1 and ORA59, which act upstream of PDF1.2, was slightly increased (ERF1) or unaffected (ORA59). PDF1.2 expression can be restored in the tga256 mutant by increased expression of ORA59, as observed in the tga256 jin1 quadruple mutant, which lacks the transcription factor JIN1/AtMYC2 that functions as a negative regulator of the JA/ET-dependent anti-fungal defense program. Whereas JA/ET-induced PDF1.2 expression is strongly suppressed by SA in wild-type plants, no negative effect of SA on PDF1.2 expression was observed in the tga256 jin1 quadruple mutant. These results imply that the antagonistic effects of TGA factors and JIN1/AtMYC2 on the JA/ET pathway are necessary to evoke the SA-mediated suppression of JA/ET-induced defense responses.

The ABC transporter BcatrB from Botrytis cinerea exports camalexin and is a virulence factor on Arabidopsis thaliana.

Arabidopsis thaliana is known to produce the phytoalexin camalexin in response to abiotic and biotic stress. Here we studied the mechanisms of tolerance to camalexin in the fungus Botrytis cinerea, a necrotrophic pathogen of A. thaliana. Exposure of B. cinerea to camalexin induces expression of BcatrB, an ABC transporter that functions in the efflux of fungitoxic compounds. B. cinerea inoculated on wild-type A. thaliana plants yields smaller lesions than on camalexin-deficient A. thaliana mutants. A B. cinerea strain lacking functional BcatrB is more sensitive to camalexin in vitro and less virulent on wild-type plants, but is still fully virulent on camalexin-deficient mutants. Pre-treatment of A. thaliana with UV-C leads to increased camalexin accumulation and substantial resistance to B. cinerea. UV-C-induced resistance was not seen in the camalexin-deficient mutants cyp79B2/B3, cyp71A13, pad3 or pad2, and was strongly reduced in ups1. Here we demonstrate that an ABC transporter is a virulence factor that increases tolerance of the pathogen towards a phytoalexin, and the complete restoration of virulence on host plants lacking this phytoalexin.

Transcriptome responses to aluminum stress in roots of aspen (Populus tremula).

BACKGROUND: Ionic aluminum (mainly Al3+) is rhizotoxic and can be present in acid soils at concentrations high enough to inhibit root growth. Many forest tree species grow naturally in acid soils and often tolerate high concentrations of Al. Previously, we have shown that aspen (Populus tremula) releases citrate and oxalate from roots in response to Al exposure. To obtain further insights into the root responses of aspen to Al, we investigated root gene expression at Al conditions that inhibit root growth. RESULTS: Treatment of the aspen roots with 500 µM Al induced a strong inhibition of root growth within 6 h of exposure time. The root growth subsequently recovered, reaching growth rates comparable to that of control plants. Changes in gene expression were determined after 6 h, 2 d, and 10 d of Al exposure. Replicated transcriptome analyses using the Affymetrix poplar genome array revealed a total of 175 significantly up-regulated and 69 down-regulated genes, of which 70% could be annotated based on Arabidopsis genome resources. Between 6 h and 2 d, the number of responsive genes strongly decreased from 202 to 26, and then the number of changes remained low. The responses after 6 h were characterized by genes involved in cell wall modification, ion transport, and oxidative stress. Two genes with prolonged induction were closely related to the Arabidopsis Al tolerance genes ALS3 (for Al sensitive 3) and MATE (for multidrug and toxin efflux protein, mediating citrate efflux). Patterns of expression in different plant organs and in response to Al indicated that the two aspen genes are homologs of the Arabidopsis ALS3 and MATE. CONCLUSION: Exposure of aspen roots to Al results in a rapid inhibition of root growth and a large change in root gene expression. The subsequent root growth recovery and the concomitant reduction in the number of responsive genes presumably reflect the success of the roots in activating Al tolerance mechanisms. The aspen genes ALS3 and MATE may be important components of these mechanisms.

Wounding of Arabidopsis leaves causes a powerful but transient protection against Botrytis infection.

SUMMARY: Physical injury inflicted on living tissue makes it vulnerable to invasion by pathogens. Wounding of Arabidopsis thaliana leaves, however, does not conform to this concept and leads to immunity to Botrytis cinerea, the causal agent of grey mould. In wounded leaves, hyphal growth was strongly inhibited compared to unwounded controls. Wound-induced resistance was not associated with salicylic acid-, jasmonic acid- or ethylene-dependent defence responses. The phytoalexin camalexin was found to be involved in this defence response as camalexin-deficient mutants were not protected after wounding and the B. cinerea strains used here were sensitive to this compound. Wounding alone did not lead to camalexin production but primed its accumulation after inoculation with B. cinerea, further supporting the role of camalexin in wound-induced resistance. In parallel with increased camalexin production, genes involved in the biosynthesis of camalexin were induced faster in wounded and infected plants in comparison with unwounded and infected plants. Glutathione was also found to be required for resistance, as mutants deficient in gamma-glutamylcysteine synthetase showed susceptibility to B. cinerea after wounding, indicating that wild-type basal levels of glutathione are required for the wound-induced resistance. Furthermore, expression of the gene encoding glutathione-S-transferase 1 was primed by wounding in leaves inoculated with B. cinerea. In addition, the priming of MAP kinase activity was observed after inoculation of wounded leaves with B. cinerea compared to unwounded inoculated controls. Our results demonstrate how abiotic stress can induce immunity to virulent strains of B. cinerea, a process that involves camalexin and glutathione.

Salicylic acid production in response to biotic and abiotic stress depends on isochorismate in Nicotiana benthamiana.

Salicylic acid (SA) is an important signal involved in the activation of defence responses against abiotic and biotic stress. In tobacco, benzoic acid or glucosyl benzoate were proposed to be precursors of SA. This is in sharp contrast with studies in Arabidopsis thaliana, where SA derives from isochorismate. We have determined the importance of isochorismate for SA biosynthesis in Nicotiana benthamiana using virus-induced gene silencing of the isochorismate synthase (ICS) gene. Plants with silenced ICS expression do not accumulate SA after exposure to UV or to pathogen stress. Plants with silenced ICS expression also exhibit strongly decreased levels of phylloquinone, a product of isochorismate. Our data provide evidence for an isochorismate-derived synthesis of SA in N. benthamiana.

FiRe and microarrays: a fast answer to burning questions.

FiRe is a user-friendly Excel macro designed to survey microarray data rapidly. This software interactively assembles data from different experiments and produces lists of candidate genes according to patterns of gene expression. Furthermore, macros bundled with FiRe can compare lists of genes, merge information from different spreadsheets, link candidates to information available from web-based databases, and produce heat-maps for easy visualization of microarray data. FiRe is freely available at http://www.unifr.ch/plantbio/FiRe/main.html .