Showing papers on "Systemic acquired resistance published in 1998"
TL;DR: Rhizobacteria-mediated induced systemic resistance (ISR) is effective under field conditions and offers a natural mechanism for biological control of plant disease.
Abstract: Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species, and plants show variation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, siderophores, and salicylic acid (SA). Whereas some of the rhizobacteria induce resistance through the SA-dependent SAR pathway, others do not and require jasmonic acid and ethylene perception by the plant for ISR to develop. No consistent host plant alterations are associated with the induced state, but upon challenge inoculation, resistance responses are accelerated and enhanced. ISR is effective under field conditions and offers a natural mechanism for biological control of plant disease.
2,146 citations
TL;DR: Evidence is provided that the processes downstream of NPR1 in the ISR pathway are divergent from those in the SAR pathway, indicating that NPR1 differentially regulates defense responses, depending on the signals that are elicited during induction of resistance.
Abstract: Plants have the ability to acquire an enhanced level of resistance to pathogen attack after being exposed to specific biotic stimuli. In Arabidopsis, nonpathogenic, root-colonizing Pseudomonas fluorescens bacteria trigger an induced systemic resistance (ISR) response against infection by the bacterial leaf pathogen P. syringae pv tomato. In contrast to classic, pathogen-induced systemic acquired resistance (SAR), this rhizobacteria-mediated ISR response is independent of salicylic acid accumulation and pathogenesis-related gene activation. Using the jasmonate response mutant jar1 , the ethylene response mutant etr1 , and the SAR regulatory mutant npr1 , we demonstrate that signal transduction leading to P. fluorescens WCS417r‐mediated ISR requires responsiveness to jasmonate and ethylene and is dependent on NPR1. Similar to P. fluorescens WCS417r, methyl jasmonate and the ethylene precursor 1-aminocyclopropane-1-carboxylate were effective in inducing resistance against P. s. tomato in salicylic acid‐nonaccumulating NahG plants. Moreover, methyl jasmonate‐induced protection was blocked in jar1 , etr1 , and npr1 plants, whereas 1-aminocyclopropane-1-carboxylate‐induced protection was affected in etr1 and npr1 plants but not in jar1 plants. Hence, we postulate that rhizobacteria-mediated ISR follows a novel signaling pathway in which components from the jasmonate and ethylene response are engaged successively to trigger a defense reaction that, like SAR, is regulated by NPR1. We provide evidence that the processes downstream of NPR1 in the ISR pathway are divergent from those in the SAR pathway, indicating that NPR1 differentially regulates defense responses, depending on the signals that are elicited during induction of resistance.
1,154 citations
TL;DR: It is shown that inoculation of Arabidopsis leaves with avirulent Pseudomonas syringae induces secondary oxidative bursts in discrete cells in distant tissues, leading to low-frequency systemic micro-HRs.
1,129 citations
TL;DR: It is demonstrated that jasmonic acid and ethylene are important for the induction of nonspecific disease resistance through signaling pathways that are distinct from the classical systemic acquired resistance response pathway regulated by salicylic acid.
701 citations
TL;DR: It is found that NPR1 confers resistance to the pathogens Pseudomonas syringae and Peronospora parasitica in a dosage-dependent fashion and is shown to be a workable target for genetic engineering of nonspecific resistance in plants.
Abstract: The recently cloned NPR1 gene of Arabidopsis thaliana is a key regulator of acquired resistance responses. Upon induction, NPR1 expression is elevated and the NPR1 protein is activated, in turn inducing expression of a battery of downstream pathogenesis-related genes. In this study, we found that NPR1 confers resistance to the pathogens Pseudomonas syringae and Peronospora parasitica in a dosage-dependent fashion. Overexpression of NPR1 leads to enhanced resistance with no obvious detrimental effect on the plants. Thus, for the first time, a single gene is shown to be a workable target for genetic engineering of nonspecific resistance in plants.
538 citations
TL;DR: The dnd1 mutant demonstrates that strong restriction of pathogen growth can occur in the absence of extensive HR cell death in the gene-for-gene resistance response of Arabidopsis against P. syringae.
Abstract: The cell death response known as the hypersensitive response (HR) is a central feature of gene-for-gene plant disease resistance. A mutant line of Arabidopsis thaliana was identified in which effective gene-for-gene resistance occurs despite the virtual absence of HR cell death. Plants mutated at the DND1 locus are defective in HR cell death but retain characteristic responses to avirulent Pseudomonas syringae such as induction of pathogenesis-related gene expression and strong restriction of pathogen growth. Mutant dnd1 plants also exhibit enhanced resistance against a broad spectrum of virulent fungal, bacterial, and viral pathogens. The resistance against virulent pathogens in dnd1 plants is quantitatively less strong and is differentiable from the gene-for-gene resistance mediated by resistance genes RPS2 and RPM1. Levels of salicylic acid compounds and mRNAs for pathogenesis-related genes are elevated constitutively in dnd1 plants. This constitutive induction of systemic acquired resistance may substitute for HR cell death in potentiating the stronger gene-for-gene defense response. Although cell death may contribute to defense signal transduction in wild-type plants, the dnd1 mutant demonstrates that strong restriction of pathogen growth can occur in the absence of extensive HR cell death in the gene-for-gene resistance response of Arabidopsis against P. syringae.
468 citations
TL;DR: Several inducible in vivo footprints located at or nearby these motifs demonstrate significant and highly reproducible changes in DNA accessibility following SAR induction, tightly correlated with the functionally important regions of the promoter identified by mutation analysis.
Abstract: 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. Additionally, two 10-bp linker-scanning mutations centered at 640 bp and 610 bp upstream from the transcription initiation site are each sufficient to abolish chemical inducibility of a GUS reporter fusion. The -640 linker-scanning mutation encompasses a region highly homologous to recognition sites for transcription factors of the basic leucine zipper class, while the -610 linker-scanning mutation contains a sequence similar to a consensus recognition site for the transcription factor NF-kappa B. Furthermore, several inducible in vivo footprints located at or nearby these motifs demonstrate significant and highly reproducible changes in DNA accessibility following SAR induction. This in vivo signature of protein-DNA interactions after INA induction is tightly correlated with the functionally important regions of the promoter identified by mutation analysis.
389 citations
TL;DR: Introduction of pchBA into CHA0 increased the production of salicylic acid in vitro and in the rhizosphere of tobacco, but did not improve the ability ofCHA0 to induce systemic resistance in tobacco.
Abstract: Application of salicylic acid induces systemic acquired resistance in tobacco. pchA and pchB, which encode for the biosynthesis of salicylic acid in Pseudomonas aeruginosa, were cloned into two expression vectors, and these constructs were introduced into two root-colonizing strains of P. fluorescens. Introduction of pchBA into strain P3, which does not produce salicylic acid, rendered this strain capable of salicylic acid production in vitro and significantly improved its ability to induce systemic resistance in tobacco against tobacco necrosis virus. Strain CHA0 is a well-described biocontrol agent that naturally produces salicylic acid under conditions of iron limitation. Introduction of pchBA into CHA0 increased the production of salicylic acid in vitro and in the rhizosphere of tobacco, but did not improve the ability of CHA0 to induce systemic resistance in tobacco. In addition, these genes did not improve significantly the capacity of strains P3 and CHA0 to suppress black root rot of tobac...
345 citations
TL;DR: Results from a biocontrol agent-fortified compost mix induced systemic acquired resistance (SAR) in cucumber against anthracnose caused by Colletotrichum orbiculare and in Arabidopsis against bacterial speck caused by Pseudomonas syringae pv.
Abstract: A biocontrol agent-fortified compost mix, suppressive to several diseases caused by soilborne plant pathogens, induced systemic acquired resistance (SAR) in cucumber against anthracnose caused by Colletotrichum orbiculare and in Arabidopsis against bacterial speck caused by Pseudomonas syringae pv maculicola KD4326 A peat mix conducive to soilborne diseases did not induce SAR The population size of P syringae pv maculicola KD4326 was significantly lower in leaves of Arabidopsis plants grown in the compost mix compared to those grown in the peat mix Autoclaving destroyed the SAR-inducing effect of the compost mix, and inoculation of the autoclaved mix with nonautoclaved compost mix or Pantoea agglomerans 278A restored the effect, suggesting the SAR-inducing activity of the compost mix was biological in nature Topical sprays with water extract prepared from the compost mix reduced symptoms of bacterial speck and the population size of pathogenic KD4326 in Arabidopsis grown in the peat mix bu
289 citations
TL;DR: Results show that CPR6 is an important regulator of multiple signal transduction pathways involved in plant defense, as well as the identification of another component, CPR6, that may function with NPR1 in regulating PR gene expression.
Abstract: In Arabidopsis, NPR1 mediates the salicylic acid (SA)-induced expression of pathogenesis-related (PR) genes and systemic acquired resistance (SAR). Here, we report the identification of another component, CPR 6, that may function with NPR1 in regulating PR gene expression. The dominant CPR 6-1 mutant expresses the SA/NPR1-regulated PR genes (PR-1, BGL 2, and PR-5) and displays enhanced resistance to Pseudomonas syringae pv maculicola ES4326 and Peronospora parasitica Noco2 in the absence of SAR induction. cpr 6-1-induced PR gene expression is not suppressed in the cpr 6-1 npr1-1 double mutant but is suppressed when SA is removed by salicylate hydroxylase. Thus, constitutive PR gene expression in cpr 6-1 requires SA but not NPR1. In addition, resistance to P. s. maculicola ES4326 is suppressed in the cpr 6-1 npr1-1 double mutant, despite expression of PR-1, BGL 2, and PR-5. Resistance to P. s. maculicola ES4326 must therefore be accomplished through unidentified antibacterial gene products that are regulated through NPR1. These results show that CPR 6 is an important regulator of multiple signal transduction pathways involved in plant defense.
286 citations
TL;DR: The existence of chemically inducible disease resistance and PR-1 andPR-5 gene expression in maize indicates that maize is similar to dicots in many aspects of induced resistance, which reinforces the notion of an ancient plant-inducible defense pathway against pathogen attack that is shared between monocots and dicot.
Abstract: 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...
TL;DR: It is reported that the overexpression of Prf leads to enhanced resistance to a number of normally virulent bacterial and viral pathogens and leads to increased sensitivity to fenthion.
Abstract: Resistance in tomato to the bacterial pathogen Pseudomonas syringae pathovar tomato requires Pto and Prf. Mutations that eliminate Prf show a loss of both Pto resistance and sensitivity to the organophosphate insecticide fenthion, suggesting that Prf controls both phenotypes. Herein, we report that the overexpression of Prf leads to enhanced resistance to a number of normally virulent bacterial and viral pathogens and leads to increased sensitivity to fenthion. These plants express levels of salicylic acid comparable to plants induced for systemic acquired resistance (SAR) and constitutively express pathogenesis related genes. These results suggest that the overexpression of Prf activates the Pto and Fen pathways in a pathogen-independent manner and leads to the activation of SAR. Transgene-induced SAR has implications for the generation of broad spectrum disease resistance in agricultural crop plants.
TL;DR: In this review the latest developments implicating salicylic acid as a signal molecule in systemic resistance are discussed and contrasted with new signalling pathways which, seemingly, are based on alternative mechanisms.
TL;DR: The ability of various chemicals to enhance plant disease resistance correlated with their capability to potentiate parsley PAL gene elicitation, emphasizing an important role for defense response potentiation in acquired plant disease resistant.
Abstract: Systemic acquired resistance is an important component of the disease-resistance arsenal of plants, and is associated with an enhanced potency for activating local defense responses upon pathogen attack Here we demonstrate that pretreatment with benzothiadiazole (BTH), a synthetic activator of acquired resistance in plants, augmented the sensitivity for low-dose elicitation of coumarin phytoalexin secretion by cultured parsley (Petroselinum crispum L) cells Enhanced coumarin secretion was associated with potentiated activation of genes encoding Phe ammonia-lyase (PAL) The augmentation of PAL gene induction was proportional to the length of pretreatment with BTH, indicating time-dependent priming of the cells In contrast to the PAL genes, those for anionic peroxidase were directly induced by BTH in the absence of elicitor, thus confirming a dual role for BTH in the activation of plant defenses Strikingly, the ability of various chemicals to enhance plant disease resistance correlated with their capability to potentiate parsley PAL gene elicitation, emphasizing an important role for defense response potentiation in acquired plant disease resistance
TL;DR: It is reported that while anionic peroxidase and mannitol dehydrogenase encoding genes are directly responsive to SA, pretreating parsley cells with SA not only enhances elicitation of the phenylpropanoid genes phenylalanine ammonia-lyase and 4-coumarate:CoA ligase but also of genes for PR-10 and a hydroxyproline-rich glycoprotein.
Abstract: Summary
Systemic acquired resistance is an inducible plant defence state, the activation of which depends mostly on the accumulation of salicylic acid (SA). During the past several years, it has been demonstrated that pretreatment of cultured parsley cells with SA potentiates the elicitation of several defence responses that are local in whole plants, including the accumulation of phenylpropanoid products. Here it is reported that while anionic peroxidase and mannitol dehydrogenase encoding genes are directly responsive to SA, pretreating parsley cells with SA not only enhances elicitation of the phenylpropanoid genes phenylalanine ammonia-lyase and 4-coumarate:CoA ligase but also of genes for PR-10 and a hydroxyproline-rich glycoprotein. Enhanced induction of these genes was seen at low levels of endogenous free SA. Enhancement of phenylalanine ammonia-lyase gene activation was proportional to the length of SA pretreatment. Furthermore, the ability of SA analogues to both potentiate elicited and directly induce defence gene activation correlated with their biological activity to promote plant disease resistance. In summary, these results emphasize that SA has at least a dual role in plant defence gene activation.
TL;DR: Results suggest an involvement of Rhizobium-synthesized Nod factors in the inhibition of salicylic acid-mediated defense in legumes.
Abstract: Inoculation of alfalfa plants with either incompatible Rhizobium or a Rhizobium mutant blocked in Nod factor synthesis led to an accumulation of salicylic acid in roots, in contrast to plants inoculated with a wild-type (compatible) R. meliloti strain. When salicylic acid was exogenously applied prior to inoculation of alfalfa plants with either purified Nod factor or compatible Rhizobium strains, a significant inhibition of nodule primordia formation and a reduction of the number of emerging nodules, respectively, as well as a delay in nodule visualization, were observed. These results suggest an involvement of Rhizobium-synthesized Nod factors in the inhibition of salicylic acid-mediated defense in legumes.
TL;DR: To determine if replication of viruses other than TMV could be inhibited by SA and, if so, whether the resistance to other viruses could also be prevented by SHAM, 14CO2-feeding experiments indicated that SA-induced interference with long-distance movement of the virus was detected.
Abstract: Salicylic acid (SA) treatment has recently been reported to inhibit replication of tobacco mosaic virus (TMV) in inoculated tissue. Furthermore, resistance is induced via a novel defensive signal transduction pathway sensitive to inhibition by salicylhydroxamic acid (SHAM; S. Chivasa, A. M. Murphy, M. Naylor, and J. P. Carr, Plant Cell 9: 547–557, 1997). The goals of this study were to determine if replication of viruses other than TMV could be inhibited by SA and, if so, whether the resistance to other viruses could also be prevented by SHAM. Potato virus X (PVX) RNA accumulation in inoculated tobacco leaf tissue was reduced by SA treatment and resistance was dependent on the SHAM-sensitive signaling pathway. However, although symptoms of cucumber mosaic virus (CMV) infection were delayed in SA-treated tobacco plants, this was not due to inhibition of replication but rather to inhibition of systemic movement of the virus. 14CO2-feeding experiments indicated that SA-induced interference with long-distance...
TL;DR: The data presented here indicate that eds genes define a variety of components involved in limiting pathogen growth, that many additional EDS genes remain to be discovered, and that direct screens for mutants with altered susceptibility to pathogens are helpful in the dissection of complex pathogen response pathways in plants.
Abstract: To identify plant defense components that are important in restricting the growth of virulent pathogens, we screened for Arabidopsis mutants in the accession Columbia (carrying the transgene BGL2-GUS) that display enhanced disease susceptibility to the virulent bacterial pathogen Pseudomonas syringae pv. maculicola (Psm) ES4326. Among six (out of a total of 11 isolated) enhanced disease susceptibility (eds) mutants that were studied in detail, we identified one allele of the previously described npr1/nim1/sai1 mutation, which is affected in mounting a systemic acquired resistance response, one allele of the previously identified EDS5 gene, and four EDS genes that have not been previously described. The six eds mutants studied in detail (npr1-4, eds5-2, eds10-1, eds11-1, eds12-1, and eds13-1) displayed different patterns of enhanced susceptibility to a variety of phytopathogenic bacteria and to the obligate biotrophic fungal pathogen Erysiphe orontii, suggesting that particular EDS genes have pathogen-specific roles in conferring resistance. All six eds mutants retained the ability to mount a hypersensitive response and to restrict the growth of the avirulent strain Psm ES4326/avrRpt2. With the exception of npr1-4, the mutants were able to initiate a systemic acquired resistance (SAR) response, although enhanced growth of Psm ES4326 was still detectable in leaves of SAR-induced plants. The data presented here indicate that eds genes define a variety of components involved in limiting pathogen growth, that many additional EDS genes remain to be discovered, and that direct screens for mutants with altered susceptibility to pathogens are helpful in the dissection of complex pathogen response pathways in plants.
TL;DR: It is demonstrated that in Arabidopsis, the innate plant defense mechanism contributes to the effectiveness of fungicides, and the idea that pathogen defense mechanisms are under positive feedback control is supported.
Abstract: Fungicide action is generally assumed to be dependent on an antibiotic effect on a target pathogen, although a role for plant defense mechanisms as mediators of fungicide action has not been excluded. Here, we demonstrate that in Arabidopsis, the innate plant defense mechanism contributes to the effectiveness of fungicides. In NahG and nim1 (for noninducible immunity) Arabidopsis plants, which normally exhibit increased susceptibility to pathogens, the fungicides metalaxyl, fosetyl, and Cu(OH)2 are much less active and fail to control Peronospora parasitica. In contrast, the effectiveness of these fungicides is not altered in Arabidopsis mutants defective in the ethylene or jasmonic acid signal transduction pathways. Application of the systemic acquired resistance activator benzothiadiazole (BTH) in combination with these fungicides results in a synergistic effect on pathogen resistance in wild-type plants and an additive effect in NahG and BTH-unresponsive nim1 plants. Interestingly, BTH treatment normally induces long-lasting pathogen protection; however, in NahG plants, the protection is transient. These observations suggest that BTH treatment can compensate only partially for an impaired signal transduction pathway and support the idea that pathogen defense mechanisms are under positive feedback control. These observations are strikingly reminiscent of the reduced efficacy of antifungal agents in immunocompromised animals.
TL;DR: Pokeweed antiviral protein II expressed in transgenic tobacco was correctly processed to the mature form as in pokeweed and accumulated to at least 10-fold higher levels than wild-type PAP, indicating that PAPII is less toxic than PAP.
Abstract: Pokeweed antiviral protein II (PAPII), a 30 kDa protein isolated from leaves of Phytolacca americana, inhibits translation by catalytically removing a specific adenine residue from the large rRNA of the 60S subunit of eukaryotic ribosomes. The protein sequence of PAPII shows only 41% identity to PAP and PAP-S, two other antiviral proteins isolated from pokeweed. We isolated a cDNA corresponding to PAPII and introduced it into tobacco plants. PAPII expressed in transgenic tobacco was correctly processed to the mature form as in pokeweed and accumulated to at least 10-fold higher levels than wild-type PAP. We had previously observed a significant decrease in transformation frequency with PAP and recovered only two transgenic lines expressing 1–2 ng per mg protein. In contrast, eight different transgenic lines expressing up to 250 ng/mg PAPII were recovered, indicating that PAPII is less toxic than PAP. Two symptomless transgenic lines expressing PAPII were resistant to tobacco mosaic virus, potato virus X and the fungal pathogen Rhizoctonia solani. The level of viral and fungal resistance observed correlated well with the amount of PAPII protein accumulated. Pathogenesis-related protein PR1 was constitutively expressed in transgenic lines expressing PAPII. Although PR1 was constitutively expressed, no increase in salicylic acid levels was detected, indicating that PAPII may elicit a salicylic acid-independent signal transduction pathway.
TL;DR: The absence of both induced PR-1 proteins and a hypersensitive response indicated that resistance to WClMV was independent of systemic acquired resistance, and the expression of PR-proteins may be the result of viral-induced hormone imbalance.
TL;DR: The results suggest that treating leaves with P. janczewskii or its culture filtrate triggers the signal transduction cascade, activating different defence genes in melon and cotton, thus protecting the lower parts of the stem.
TL;DR: C cultured parsley cells provide a suitable system for the identification of SAR-inducing agents and the artificial sweetener saccharin, a substance not previously reported to induce SAR in plants, was found to be very effective in conditioning cells for an enhanced accumulation of coumarin derivatives.
TL;DR: Transgenic tobacco plants expressing an inhibitor of ubiquitin-dependent protein degradation, ubR48, spontaneously formed necrotic lesions and displayed altered responsiveness to tobacco mosaic virus attack and accumulation of defense-related compounds and the expression of pathogenesis-related proteins.
Abstract: Transgenic tobacco plants expressing an inhibitor of ubiquitin-dependent protein degradation, ubiquitin variant ubR48, spontaneously formed necrotic lesions and displayed altered responsiveness to tobacco mosaic virus attack. These plants were analyzed for the accumulation of defense-related compounds and the expression of pathogenesis-related proteins, which serve as convenient markers for systemic acquired resistance. Callose was detected in the cells of vascular bundles and in the leaf blade. In addition, ubR48 transgenic plants constitutively accumulated enhanced levels of salicylic acid (SA) and/or its glucoside. Accumulation of SA glucoside coincided with high levels of pathogenesis-related protein 1, underscoring the similarity of certain changes in ubR48-expressing plants to an authentic defense reaction.
TL;DR: Major recent advances in the cloning and sequencing of clustered plant disease-resistance genes are providing information on the basis of their recognitional specificities and offer the opportunity to engineer new genes that recognize refractory pathogens or exhibit increased efficacy and durability.
TL;DR: Genetic dissection of the various responses that plants activate upon recognition of pathogen attack have made clear that the plant is able to induce not only local defenses but also a carefully regulated mixture of different systemically induced defense mechanisms.
TL;DR: Results are consistent with the existence of a pathogen-induced, salicylate- independent systemic signaling pathway, possibly involving ethylene and jasmonate signaling components, in both tobacco and Arabidopsis.
TL;DR: The relationship between free SA levels in the inoculated leaf and SAR induction in tobacco supports the previous conclusion that SA is not likely to be the systemic signal.
Abstract: Salicylic acid (SA) has been proposed as the systemic signal for the induction of systemic acquired resistance (SAR). It has been suggested that SA is synthesized at the site of pathogen-induced necrosis and is translocated to induce SAR in uninfected leaves. Grafting studies between wild-type tobacco plants and plants that are unable to accumulate significant amounts of SA have shown that the large increase in SA accumulation seen in inoculated leaves is not necessary for SAR induction, suggesting that SA is not the primary systemic signal. However, these studies have not addressed whether decreased levels of SA accumulation in inoculated leaves are sufficient to fully induce SAR. In this study, we have determined the relationship between free SA levels in the inoculated leaf and SAR induction in tobacco. These results support our previous conclusion that SA is not likely to be the systemic signal.
01 Jan 1998
TL;DR: These results demonstrate that compared to pathogens inducing SAR, non-pathogenic rhizobacteria inducing ISR trigger a different signal-transduction pathway not dependent on the accumulation of SA and activation of PR-genes, but dependent on perception of ethylene and jasmonic acid.
Abstract: Treatment of plants with selected strains of plant growth-promoting rhizobacteria (PGPR) can induce systemic resistance in carnation, cucumber, radish, tobacco, and Arabidopsis as evidenced by an enhanced defensive capacity upon challenge inoculation with a pathogen. In the induction of resistance by Pseudomonas spp. in carnation, radish, and Arabidopsis, the O-antigenic side chain of the bacterial outer membrane lipopolysaccharide acts as an inducing determinant, but other bacterial traits are also involved. Siderophores have been implicated in the induction of resistance in tobacco and Arabidopsis, and a novel type of sideophore, fluorebactin, may explain induction of resistance associated with salicylic acid (SA) in radish. Although some bacterial strains are equally effective in inducing resistance in different plant species, others show specificity which suggests specific recognition between bacteria and plants at the root surface. Moreover, genetic variation for inducibility by specific PGPR strains is present in carnation and Arabidopsis. In contrast to the phenotypically similar systemic acquired resistance (SAR) induced by pathogens, PGPR-mediated induced systemic resistance (ISR) does not always require SA. SAR-associated SA production induces pathogenesis-related proteins (PRs), but no accumulation of PRs was detectable in radish and Arabidopsis expressing ISR. In addition, ISR is fully expressed in Arabidopsis plants transformed with the NahG gene and unable to accumulate SA. In contrast, Arabidopsis mutated in the Etrl gene and insensitive to ethylene, or in the jarl gene and insensitive to jasmonic acid, were no longer inducible. These results demonstrate that compared to pathogens inducing SAR, non-pathogenic rhizobacteria inducing ISR trigger a different signal-transduction pathway not dependent on the accumulation of SA and activation of PR-genes, but dependent on perception of ethylene and jasmonic acid.
TL;DR: Molecular biology is making it possible to identify both the genes and the gene products involved in infection and disease and then to direct control strategies at these genes and gene products, and some of the most remarkable advances and biggest surprises have come from studies of plant diseases.
Abstract: Molecular biology is making it possible to identify both the genes and the gene products involved in infection and disease and then to direct control strategies at these genes and gene products. Understandably, the vast majority of this kind of research and development continues to be directed at human diseases, but some of the most remarkable advances and biggest surprises have come from studies of plant diseases. Of course, plants, not having a circulatory system and ability to make antibodies, depend on very different defense strategies than those used by animals. Plants with ability to resist infection by a particular pathogen are referred to as “resistant” to that pathogen, and pathogens lacking the ability to attack a particular plant are referred to as “avirulent” on that plant. Research begun shortly after the rediscovery of Mendel’s laws showed that resistance is heritable and plant breeders have been breeding varieties of crop plants with disease resistance ever since. Unfortunately for agriculture, the pathogen is adaptive by its ability to continually evolve strains that defeat the resistance genes deployed in crop plants by plant breeders. This has led to the treadmill of continually updating and replacing varieties with different genes or combinations of genes for resistance in response to the ever-changing …