Functional analysis of regulatory sequences controlling PR-1 gene expression in Arabidopsis.

The Arabidopsis PR-1 gene is one of a suite of genes induced co-ordinately during the onset of systemic acquired resistance (SAR), a plant defense pathway triggered by pathogen infection or exogenous application of chemicals such as salicylic acid (SA) and 2,6-dichloroisonicotinic acid (INA). We have characterized cis-acting regulatory elements in the PR-1 promoter involved in INA induction using deletion analysis, linker-scanning mutagenesis, and in vivo footprinting. Compared to promoter fragments of 815 bp or longer (which show greater than 10-fold inducibility after INA treatment), induction of a 698 bp long promoter fragment is reduced by half and promoter fragments of 621 bp or shorter have lost all inducibility.

Induced resistance responses in maize.

Systemic acquired resistance (SAR) is a widely distributed plant defense system that confers broad-spectrum disease resistance and is accompanied by coordinate expression of the so-called SAR genes. This type of resistance and SAR gene expression can be mimicked with chemical inducers of resistance. Here, we report that chemical inducers of resistance are active in maize.

Characterization of Post-Transcriptionally Suppressed Transgene Expression That Confers Resistance to Tobacco Etch Virus Infection in Tobacco.

Tobacco lines expressing transgenes that encode tobacco etch virus (TEV) coat protein (CP) mRNA with or without nonsense codons give rise to TEV-resistant tissues that have reduced levels of TEV CP mRNA while maintaining high levels of transgene transcriptional activity. Two phenotypes for virus resistance in the lines containing the transgene have been described: immune (no virus infection) and recovery (initial systemic symptoms followed by gradual recovery over several weeks). Here, we show that at early times in development, immune lines are susceptible to TEV infection and accumulate full-length CP mRNA.

The Arabidopsis NIM1 protein shows homology to the mammalian transcription factor inhibitor I kappa B.

The NIM1 (for noninducible immunity) gene product is involved in the signal transduction cascade leading to both systemic acquired resistance (SAR) and gene-for-gene disease resistance in Arabidopsis. We have isolated and characterized five new alleles of nim1 that show a range of phenotypes from weakly impaired in chemically induced pathogenesis-related protein-1 gene expression and fungal resistance to very strongly blocked. We have isolated the NIM1 gene by using a map-based cloning procedure.

Suppression and Restoration of Lesion Formation in Arabidopsis lsd Mutants.

Systemic acquired resistance (SAR) is a broad-spectrum, systemic defense response that is activated in many plant species after pathogen infection. We have previously described Arabidopsis mutants that constitutively express SAR and concomitantly develop lesions simulating disease (lsd). Here, we describe two new mutants, lsd6 and lsd7, that develop spontaneous necrotic lesions and possess elevated levels of salicylic acid (SA) as well as heightened disease resistance, similar to the previously characterized lsd and accelerated cell death (acd2) mutants.

Systemic acquired resistance in Arabidopsis requires salicylic acid but not ethylene.

Systemic acquired resistance (SAR) is an inducible plant response to infection by a necrotizing pathogen. In the induced plant, SAR provides broad-spectrum protection against not only the inducing pathogen, but also against other, unrelated pathogens. Both salicylic acid (SA) and SAR-gene expression have been implicated as playing important roles in the initiation and maintenance of SAR.

Isolation and expression of three gibberellin 20-oxidase cDNA clones from Arabidopsis.

Using degenerate oligonucleotide primers based on a pumpkin (Cucurbita maxima) gibberellin (GA) 20-oxidase sequence, six different fragments of dioxygenase genes were amplified by polymerase chain reaction from arabidopsis thaliana genomic DNA. One of these was used to isolate two different full-length cDNA clones, At2301 and At2353, from shoots of the GA-deficient Arabidopsis mutant ga1-2. A third, related clone, YAP169, was identified in the Database of Expressed Sequence Tags.

Signal transduction in systemic acquired resistance.

Systemic acquired resistance (SAR) is an important component of plant defense against pathogen infection. Accumulation of salicylic acid (SA) is required for the induction of SAR. However, SA is apparently not the translocated signal but is involved in transducing the signal in target tissues.

A central role of salicylic Acid in plant disease resistance.

Transgenic tobacco and Arabidopsis thaliana expressing the bacterial enzyme salicylate hydroxylase cannot accumulate salicylic acid (SA). This defect not only makes the plants unable to induce systemic acquired resistance, but also leads to increased susceptibility to viral, fungal, and bacterial pathogens. The enhanced susceptibility extends even to host-pathogen combinations that would normally result in genetic resistance.

Salicylic Acid Is Not the Translocated Signal Responsible for Inducing Systemic Acquired Resistance but Is Required in Signal Transduction.

Infection of plants by necrotizing pathogens can induce broad-spectrum resistance to subsequent pathogen infection. This systemic acquired resistance (SAR) is thought to be triggered by a vascular-mobile signal that moves throughout the plant from the infected leaves. A considerable amount of evidence suggests that salicylic acid (SA) is involved in the induction of SAR.

Arabidopsis mutants simulating disease resistance response.

We describe six Arabidopsis mutants, defining at least four loci, that spontaneously form necrotic lesions on leaves. Lesions resemble those resulting from disease, but occur in the absence of pathogen. In five mutants, lesion formation correlates with expression of histochemical and molecular markers of plant disease resistance responses and with expression of genes activated during development of broad disease resistance in plants (systemic acquired resistance [SAR]).

Acquired Resistance Signal Transduction in Arabidopsis Is Ethylene Independent.

To clarify the role of ethylene in systemic acquired resistance (SAR), we conducted experiments using Arabidopsis ethylene response mutants. Plants that are nonresponsive to ethylene (i.e.

Salicylic acid as a signal molecule in plant-pathogen interactions.

Significant insight has been gained in the past year into the roles of salicylic acid (SA) in plant-pathogen interactions. The ability to accumulate SA has been shown to be essential for systemic acquired resistance in tobacco plants. Further experiments have shown that SA is apparently not a systemic, vascular-mobile signal, but rather is required for signal transduction at the local level.

Hormone response complex in a novel abscisic acid and cycloheximide-inducible barley gene.

The phytohormone, abscisic acid (ABA), plays a variety of roles during seed development and in the plant's response to environmental stresses. To study the molecular action of ABA, we have isolated a single copy ABA-induced gene, HVA22, which is mapped to barley chromosome 1. The HVA22 gene can be induced by either ABA or the protein synthesis inhibitor, cycloheximide, and addition of both inducers to barley aleurone layers has a synergistic effect on the expression of this gene.

Regulation of a hevein-like gene in Arabidopsis.

An Arabidopisis cDNA clone was isolated that encodes a protein similar to the antifungal chitin-binding protein hevein from rubber tree latex. This hevein-like (HEL) mRNA was inducible by either turnip crinkle virus infection or ethylene treatment. In addition, expression was moderately inducible by treatment with the resistance-inducing compounds salicylic acid and 2,6-dichlorisonicotinic acid.

Requirement of salicylic Acid for the induction of systemic acquired resistance.

It has been proposed that salicylic acid acts as an endogenous signal responsible for inducing systemic acquired resistance in plants. The contribution of salicylic acid to systemic acquired resistance was investigated in transgenic tobacco plants harboring a bacterial gene encoding salicylate hydroxylase, which converts salicylic acid to catechol. Transgenic plants that express salicylate hydroxylase accumulated little or no salicylic acid and were defective in their ability to induce acquired resistance against tobacco mosaic virus.

Regulation of pathogenesis-related protein-1a gene expression in tobacco.

Pathogenesis-related protein-1a (PR-1a) is a protein of unknown function that is strongly induced during the onset of systemic acquired resistance (SAR) in tobacco. The expression of PR-1a is under complex regulation that is controlled at least partially by the rate of transcription. In this study, we demonstrated that 661 bp of 5' flanking DNA was sufficient to impart tobacco mosaic virus and salicylic acid inducibility to a reporter gene.

Acquired resistance in Arabidopsis.

Acquired resistance is an important component of the complex disease resistance mechanism in plants, which can result from either pathogen infection or treatment with synthetic, resistance-inducing compounds. In this study, Arabidopsis, a tractable genetic system, is shown to develop resistance to a bacterial and a fungal pathogen following 2,6-dichloroisonicotinic acid (INA) treatment. Three proteins that accumulated to high levels in the apoplast in response to INA treatment were purified and characterized.

Coordinate Gene Activity in Response to Agents That Induce Systemic Acquired Resistance.

In a variety of plant species, the development of necrotic lesions in response to pathogen infection leads to induction of generalized disease resistance in uninfected tissues. A well-studied example of this "immunity" reaction is systemic acquired resistance (SAR) in tobacco. SAR is characterized by the development of a disease-resistant state in plants that have reacted hypersensitively to previous infection by tobacco mosaic virus.

Cloning and characterization of a cDNA encoding a mRNA rapidly-induced by ABA in barley aleurone layers.

Abscisic acid (ABA) inhibits the gibberellic acid induced synthesis of α-amylase in barley aleurone layers, yet ABA itself induces more than a dozen polypeptides (Lin & Ho, Plant Physiol 82: 289-297, 1986). As part of our effort to elucidate the molecular action of ABA in barley aleurone layers, we have isolated and characterized an ABA-induced cDNA clone, pHV A1. This cDNA clone hybridizes to an RNA species of approximately 1.

Metabolism of Abscisic Acid in Guard Cells of Vicia faba L. and Commelina communis L.

Metabolism of abscisic acid (ABA) was investigated in isolated guard cells and in mesophyll tissue of Vicia faba L. and Commelina communis L. After incubation in buffer containing [G-(3)H]+/-ABA, the tissue was extracted by grinding and the metabolites separated by thin layer chromatography.

Mode of action of abscisic Acid in barley aleurone layers : abscisic Acid induces its own conversion to phaseic Acid.

As a part of our effort to study the mode of action of abscisic acid (ABA) and its metabolites during seed germination, we have investigated the regulation of ABA metabolism in barley (Hordeum vulgare) aleurone layers and a few other plant tissues. The rate of conversion of [(3)H]ABA to [(3)H]phaseic acid (PA), the first stable metabolite of ABA, is enhanced by 2- to 5-fold in barley aleurone layers when the tissue is pretreated with ABA. However, the conversion of [(3)H]PA to [(3)H] dihydrophaseic acid (DPA), the next metabolite after PA, is not enhanced by pretreatment with either ABA or PA.

Regulation of abscisic acid metabolism in the aleurone layers of barley seeds.

The regulation of metabolism of abscisic acid has been investigated in the isolated aleurone layers of barley (Hordeum vulgare L.) seeds. The rate of conversion of abscisic acid to phaseic acid is enhanced by two to five-fold when the tissue is pretreated with 10(-5) M of this hormone.