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J L Dangl

Publications and source records attributed to J L Dangl.

At least 37 records · Page 2Linked to original sources
PubMed1997

The hypersensitive response and the induction of cell death in plants.

The hypersensitive response, or HR, is a form of cell death often associated with plant resistance to pathogen infection. Reactive oxygen intermediates and ion fluxes are proximal responses probably required for the HR. Apoptosis as defined in animal systems is, thus far, not a strict paradigm for the HR. The diversity observed in plant cell death morphologies suggests that there may be multiple pathways through which the HR can be triggered. Signals from pathogens appear to interfere with these pathways. HR may play in plants the same role as certain programmed cell deaths in animals with respect to restricting pathogen growth. In addition, the HR could regulate the defense responses of the plant in both local and distant tissues.

Journal Article↗
PubMed1997

Salicylate-independent lesion formation in Arabidopsis lsd mutants.

In many interactions of plants with pathogens, the primary host defense reaction is accompanied by plant cell death at the site of infection. The resulting lesions are correlated with the establishment of an inducible resistance in plants called systemic acquired resistance (SAR), for which salicylic acid (SA) accumulation is a critical signaling event in Arabidopsis and tobacco. In Arabidopsis, the lesions simulating disease (lsd) mutants spontaneously develop lesions in the absence of pathogen infection. Furthermore, lsd mutants express SAR marker genes when lesions are present and are resistant to the same spectrum of pathogens as plants activated for SAR by necrogenic pathogen infection. To assess the epistatic relationship between SA accumulation and cell death, transgenic Arabidopsis unable to accumulate SA due to the expression of the salicylate hydroxylase (nahG) gene were used in crosses with the dominant mutants lsd2 or lsd4. Progeny from the crosses were inhibited for SAR gene expression and disease resistance. However, these progeny retained the spontaneous cell death phenotype similar to siblings not expressing nahG. Because lesions form in the absence of SA accumulation for isd2 and lsd4, a model is suggested in which lesion formation in these two mutants is determined prior to SA accumulation in SAR signal transduction. By contrast, the loss of SAR gene expression and disease resistance in nahG-expressing lsd mutants indicates that these traits are dependent upon SA accumulation in the SAR signal transduction pathway.

Arabidopsis↗
PubMed1996

Initiation of runaway cell death in an Arabidopsis mutant by extracellular superoxide.

Reactive oxygen intermediates (ROIs) regulate apoptosis during normal development and disease in animals. ROIs are also implicated in hypersensitive resistance responses of plants against pathogens. Arabidopsis lsd1 mutants exhibited impaired control of cell death in the absence of pathogen and could not control the spread of cell death once it was initiated. Superoxide was necessary and sufficient to initiate lesion formation; it accumulated before the onset of cell death and subsequently in live cells adjacent to spreading lsd1 lesions. Thus, runaway cell death seen in lsd1 plants reflected abnormal accumulation of superoxide and lack of responsiveness to signals derived from it.

Apoptosis↗
PubMed1996

Plant pathology: many roads lead to resistance.

Recent studies suggest that plant disease-resistance responses use multiple signaling pathways acting subsequent to pathogen recognition, and that phosphorylation cascades play a prominent role in the recognition and execution of foreign invaders.

Arabidopsis Proteins↗
PubMed1995

Structure of the Arabidopsis RPM1 gene enabling dual specificity disease resistance.

Plants can recognize pathogens through the action of disease resistance (R) genes, which confer resistance to pathogens expressing unique corresponding avirulence (avr) genes. The molecular basis of this gene-for-gene specificity is unknown. The Arabidopsis thaliana RPM1 gene enables dual specificity to pathogens expressing either of two unrelated Pseudomonas syringae avr genes. Despite this function, RPM1 encodes a protein sharing molecular features with recently described single-specificity R genes. Surprisingly, RPM1 is lacking from naturally occurring, disease-susceptible Arabidopsis accessions.

Amino Acid Sequence↗
PubMed1994

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]). We designate this novel mutant class Isd (for lesions simulating disease resistance response). Strikingly, four Isd mutants express substantial resistance to virulent fungal pathogen isolates. Isd mutants vary in cell type preferences for lesion onset and spread. Lesion formation can be conditional and can be induced specifically by biotic and chemical activators of SAR in Isd1 mutants.

Arabidopsis↗
PubMed1994

Analysis of the parsley chalcone-synthase promoter in response to different light qualities.

We examined the chalcone synthase (chs) promoter from parsley [Petroselinum crispum Miller (A.W. Hill)] for the existence of separate promoter elements responsible for transcriptional activation of the chs gene by UV-B and by blue light. A combination of in-vivo foot-printing in parsley cells and light-induced transient expression assays with different chs promoter constructs in parsley protoplasts was used. Dark controls and blue-light-irradiated cells gave identical in-vivo footprints on the chs promoter. Pre-irradiation with blue light prior to a UV-B-light pulse is known to cause a shift in the timing of UV-B-light-induced increase in chs transcription rates. This shift was also manifested on the DNA template, since UV-B-light-induced in-vivo footprints in cells pretreated with blue light were detected earlier than in cells which had been irradiated with a UV-B-light pulse only. Although there was a clear shift in the timing of footprint appearance, the patterns of footprinting did not change. Light-induced transient-expression assays revealed that the shortest tested chs promoter which retained any light responsiveness, was sufficient for mediating both induction by UV light and the blue-light-mediated kinetic shift. These findings argue against a spatial separation of UV-B- and blue-light-responsive elements on the chs promoter. We interpret these data by postulating that the signal transduction pathways originating from the excitation of UV-B- and blue-light receptors merge at the chs promoter, or somewhere between light perception and protein-DNA interaction.

Acyltransferases↗
PubMed1994

Perception and response in plant disease resistance.

Plants express sophisticated mechanisms for recognizing pathogens. The functionally defined repertoire of non-self perception is large; the number and nature of subsequent molecular events required for resistance is unknown. Recent cloning of disease resistance genes, and genetic identification of loci required for their function, allows dissection of the structure, evolution, and deployment within populations of pathogen-perception mechanisms. Roles for reactive oxygen species and programmed cell death in resistance have also been suggested recently. New results document a role for salicylic acid as a lynchpin in the establishment and maintenance of the 'effector functions' of disease resistance, and strategies for engineered plant protection are moving closer to reality.

Apoptosis↗
PubMed1992

Rapid activation of a novel plant defense gene is strictly dependent on the Arabidopsis RPM1 disease resistance locus.

We cloned and sequenced cDNAs encoded by a novel plant defense gene, ELI3, from parsley and Arabidopsis thaliana. The predicted product shares no homology to known sequences. ELI3 mRNA accumulates in A. thaliana leaves in response to challenge with phytopathogenic Pseudomonas syringae strains. The timing and magnitude of this response are dictated by the genetics of the plant-pathogen interaction being analyzed. During incompatible interactions, where resistance in the plant genotype Col-0 is dictated by the dominant RPM1 locus, ELI3 mRNA accumulates to high levels 5-10 h post-inoculation. This kinetic behavior is also generated by the presence of a cloned bacterial avirulence gene, in otherwise virulent bacteria, which triggers resistance mediated via RPM1 action. The phenotypic outcome is a hypersensitive resistance reaction visible 8-15 h post-infiltration. Thus, the induction kinetics of ELI3 mRNA accumulation are consistent with a functional role for the ELI3 gene product in establishing the resistant phenotype. In contrast, during compatible interactions with the susceptible plant genotype Nd-0, which is homozygous recessive at the rpm1 locus, ELI3 mRNA accumulates significantly only after 15 h. We show genetically that ELI3 activation is strictly dependent on the presence of dominant alleles at RPM1 using an assay generalizable to any pathogen induced plant defense phenomena.

Amino Acid Sequence↗
PubMed1992

Functional homologs of the Arabidopsis RPM1 disease resistance gene in bean and pea.

We showed that a bacterial avirulence (avr) gene function, avrPpiA1, from the pea pathogen Pseudomonas syringae pv pisi, is recognized by some, but not all, genotypes of Arabidopsis. Thus, an avr gene functionally defined on a crop species is also an avr gene on Arabidopsis. The activity of avrPpiA1 on a series of Arabidopsis genotypes is identical to that of the avrRpm1 gene from P.s. pv maculicola previously defined using Arabidopsis. The two avr genes are homologous and encode nearly identical predicted products. Moreover, this conserved avr function is also recognized by some bean and pea cultivars in what has been shown to be a gene-for-gene manner. We further demonstrated that the Arabidopsis disease resistance locus, RPM1, conditioning resistance to avrRpm1, also conditions resistance to bacterial strains carrying avrPpiA1. Therefore, bean, pea, and conceivably other crop species contain functional and potentially molecular homologs of RPM1.

Amino Acid Sequence↗
PubMed1991

Exonic sequences are required for elicitor and light activation of a plant defense gene, but promoter sequences are sufficient for tissue specific expression.

The parsley 4CL-1 gene encodes 4-coumarate:CoA ligase, a key enzyme of general phenylpropanoid metabolism. As well as being transcriptionally activated by such stresses as pathogen infection, UV-irradiation, and wounding, expression of 4CL-1 is developmentally regulated. In this paper we present evidence that 4CL-1 cis-acting elements which control stress-induced and developmental expression are physically separated. The ability of a series of 4CL gene constructions to respond to elicitor and light in stably or transiently transformed parsley cells was tested. While inducible expression was observed from all templates in which the 4CL-1 structural gene was fused to the 4CL-1 promoter, fusions of the promoter to the GUS reporter gene were completely unresponsive. The element(s) required for responsiveness appear to be exonic, since 4CL-1 introns and 3' flanking DNA had no effect on inducibility. Furthermore, this unconventional regulatory mode operates in transgenic tobacco plants, where we show that a 4CL-1 promoter fragment specifies correct cell-specific expression when fused to GUS yet is unresponsive to elicitor and light.

Base Sequence↗
PubMed1991

A parsley 4CL-1 promoter fragment specifies complex expression patterns in transgenic tobacco.

The 4CL-1 gene is one of two highly homologous parsley genes encoding 4-coumarate:coenzyme A ligase, a key enzyme of general phenylpropanoid metabolism. Expression of these genes is essential for the biosynthesis of both defense-related and developmentally required phenylpropanoid derivatives. We examined the developmental regulation of the 4CL-1 promoter by analyzing the expression of 4CL-1-beta-glucuronidase fusions in transgenic tobacco plants. A 597-base pair 4CL-1 promoter fragment specified histochemically detectable expression in a complex array of vegetative and floral tissues and cell types. The activity of a series of 5' deleted promoter fragments was analyzed in parsley protoplasts and transgenic tobacco plants. Deletions past -210 base pairs led to a drastic decline in beta-glucuronidase activity in protoplasts and loss of tissue-specific expression in transgenic tobacco. These results were put into the context of potential protein-DNA interactions by in vivo footprint analysis of the 4CL-1 promoter in parsley cells. Loss of promoter activity in parsley protoplasts and transgenic tobacco was correlated with the deletion or disruption of the distal portion of a large (100-base pair) footprinted region within the first 200 base pairs of the 4CL-1 promoter.

Base Composition↗
PubMed1990

Functional borders, genetic fine structure, and distance requirements of cis elements mediating light responsiveness of the parsley chalcone synthase promoter.

The genetic fine structure of cis-acting sequences previously shown to be necessary for light-regulated expression in the promoter of the parsley (Petroselinum crispum) chalcone synthase gene was analyzed. Site-directed mutations and changes in spacing between cis elements were measured in transient expression assays in parsley protoplasts. Clustered point mutations allowed assignment of functional borders. Single-base substitutions within a highly conserved cis element (box II/G box) defined a critical core of seven bases, 5'-ACGTGGC-3'. It is functionally equivalent to a second sequence-related element (box III), which could replace box II in an orientation-dependent manner. The activity of box II required the presence of another juxtaposed element (box I) at a defined distance. No distance requirement was observed between the two large separable promoter regions known to independently confer light-regulated expression. These data support our hypothesis that a cis-acting sequence that is present in a limited number of diversely regulated plant genes gains its functional capacity and specificity by combinatorial diversity involving flanking partner elements.

Acyltransferases↗
PubMed1989

Inducible in vivo DNA footprints define sequences necessary for UV light activation of the parsley chalcone synthase gene.

We began characterization of the protein--DNA interactions necessary for UV light induced transcriptional activation of the gene encoding chalcone synthase (CHS), a key plant defense enzyme. Three light dependent in vivo footprints appear on a 90 bp stretch of the CHS promoter with a time course correlated with the onset of CHS transcription. We define a minimal light responsive promoter by functional analysis of truncated CHS promoter fusions with a reporter gene in transient expression experiments in parsley protoplasts. Two of the three footprinted sequence 'boxes' reside within the minimal promoter. Replacement of 10 bp within either of these 'boxes' leads to complete loss of light responsiveness. We conclude that these sequences define the necessary cis elements of the minimal CHS promoter's light responsive element. One of the functionally defined 'boxes' is homologous to an element implicated in regulation of genes involved in photosynthesis. These data represent the first example in a plant defense gene of an induced change in protein--DNA contacts necessary for transcriptional activation. Also, our data argue strongly that divergent light induced biosynthetic pathways share common regulatory units.

Acyltransferases↗
PubMed1989

Functional architecture of the light-responsive chalcone synthase promoter from parsley.

We have combined in vivo genomic footprinting and light-induced transient expression of chalcone synthase promoter derivatives in parsley protoplasts to identify cis sequences regulating light activation. The parsley chalcone synthase promoter contains two cis "units" that are light-responsive. Each unit is composed of short DNA stretches of approximately 50 base pairs, and each contains two in vivo footprints. One of the footprints in each unit covers a sequence that is highly conserved among other light- and stress-regulated plant genes. The other footprinted sequences in each unit are not related to each other. The TATA distal light-responsive unit is inherently weak but can compensate partially for the loss of the stronger TATA proximal unit. Levels of light-induced expression from either can be influenced by the presence of a region of approximately 100 base pairs located upstream of the TATA distal light-responsive unit. Combination of the light-responsive units and upstream region generates a synergistic response to light. We speculate that functional compensation generated by nonidentical, but sequence-related, cis units foreshadows combinatorial diversity of cognate trans factors.

Acyltransferases↗