• The Plant Pathology Journal
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• v.29 no.2
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• pp.174-181
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• 2013

The plant growth-promoting rhizobacterium Ochrobactrum lupini KUDC1013 elicited induced systemic resistance (ISR) in tobacco against soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum. We investigated of its factors involved in ISR elicitation. To characterize the ISR determinants, KUDC1013 cell suspension, heat-treated cells, supernatant from a culture medium, crude bacterial lipopolysaccharide (LPS) and flagella were tested for their ISR activities. Both LPS and flagella from KUDC1013 were effective in ISR elicitation. Crude cell free supernatant elicited ISR and factors with the highest ISR activity were retained in the n-butanol fraction. Analysis of the ISR-active fraction revealed the metabolites, phenylacetic acid (PAA), 1-hexadecene and linoleic acid (LA), as elicitors of ISR. Treatment of tobacco with these compounds significantly decreased the soft rot disease symptoms. This is the first report on the ISR determinants by plant growth-promoting rhizobacteria (PGPR) KUDC1013 and identifying PAA, 1-hexadecene and LA as ISR-related compounds. This study shows that KUDC1013 has a great potential as biological control agent because of its multiple factors involved in induction of systemic resistance against phytopathogens.

• Mycobiology
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• v.29 no.1
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• pp.19-26
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• 2001

Defense mechanisms against anthracnose disease caused by Colletotrichum orbiculare on the leaf surface of cucumber plants after pre-treatment with plant growth promoting rhizobacteria(PGPR), amino salicylic acid(ASA) or C. orbiculare were compared using a fluorescence microscope. Induced systemic resistance was mediated by the pre-inoculation in the root system with PGPR strain Bacillus amylolquefaciens EXTN-1 that showed direct antifungal activity to C. gloeosporioides and C. orbiculare. Also, systemic acquired resistance was triggered by the pre-treatments on the bottom leaves with amino salicylic acid or conidial suspension of C. orbiculare. The protection values on the leaves expressing SAR were higher compared to those expressing ISR. After pre-inoculation with PGPR strains no change of the plants was found in phenotype, while necrosis or hypersensitive reaction(HR) was observed on the leaves of plants pre-treated with ASA or the pathogen. After challenge inoculation, inhibition of fungal growth was observed on the leaves expressing both ISR and SAR. HR was frequently observed at the penetration sites of both resistance-expressing leaves. Appressorium formation was dramatically reduced on the leaves of plants pre-treated with ASA, whereas EXTN-1 did not suppress the appressorium formation. ASA also more strongly inhibited the conidial germination than EXTN-1. Conversely, EXTN-1 significantly increased the frequency of callose formation at the penetration sites, but ASA did not. The defense mechanisms induced by C. orbiculare were similar to those by ASA. Based on these results it is suggested that resistance mechanisms on the leaf surface was different between on the cucumber leaves expressing ISR and SAR, resulting in the different protection values.

• The Plant Pathology Journal
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• v.25 no.4
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• pp.389-399
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• 2009

A group of beneficial plant bacteria has been shown to increase crop growth referring to as plant growth-promoting rhizobacteria (PGPR). PGPR can decrease plant disease directly, through the production of antagonistic compounds, and indirectly, through the elicitation of a plant defense response termed induced systemic resistance (ISR). While the mechanism of PGPR-elicited ISR has been studied extensively in the model plant Arabidopsis, it is less well characterized in crop plants such as pepper. In an effort to better understand the mechanism of ISR in crop plants, we investigated the induction of ISR by Bacillus cereus strain BS107 against Xanthomonas axonopodis pv. vesicatoria in pepper leaves. We focused on the priming effect of B. cereus strain BS107 on plant defense genes as an ISR mechanism. Of ten known pepper defense genes that were previously reported to be involved in pathogen defense signaling, the expression of Capsicum annum pathogenesis-protein 4 and CaPR1 was systemically primed by the application of strain BS107 onto pepper roots confirming by quantitative-reverse transcriptase PCR. Our results provide novel genetic evidence of the priming effect of a rhizobacterium on the expression of pepper defense genes involved in ISR.

• The Plant Pathology Journal
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• v.36 no.3
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• pp.255-266
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• 2020

Plant immune responses can be triggered by chemicals, microbes, pathogens, insects, or abiotic stresses. In particular, induced systemic resistance (ISR) refers to the activation of the immune system due to a plant's interaction with beneficial microorganisms. The phenolic compound, 2,4-diacetylphloroglucinol (DAPG), which is produced by beneficial Pseudomonas spp., acts as an ISR elicitor, yet DAPG's mechanism in ISR remains unclear. In this study, transgenic Arabidopsis thaliana plants overexpressing the DAPG hydrolase gene (phlG) were generated to investigate the functioning of DAPG in ISR. DAPG was applied onto 3-week-old A. thaliana Col-0 and these primed plants showed resistance to the pathogens Botrytis cinerea and Pseudomonas syringae pv. tomato DC3000. However, in the phlG transgenic A. thaliana, the ISR was not triggered against these pathogens. The DAPG-mediated ISR phenotype was impaired in transgenic A. thaliana plants overexpressing phlG, thus showing similar disease severity when compared to untreated control plants. Furthermore, the DAPG-treated A. thaliana Col-0 showed an increase in their gene expression levels of PDF1.2 and WRKY70 but this failed to occur in the phlG transgenic lines. Collectively, these experimental results indicate that jasmonic acid/ethylene signal-based defense system is effectively disabled in phlG transgenic A. thaliana lines.

• Korean Journal of Plant Resources
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• v.23 no.3
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• pp.248-255
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• 2010

We previously demonstrated that root colonization of the rhizobacterium, Pseudomonas chlororaphis O6, induced expression of a galactinol synthase gene (CsGolS1), and resulting galactinol conferred induced systemic resistance (ISR) against fungal and bacterial pathogens in cucumber leaves. To examine the role of galactinol on ISR, drought or high salt stress, we obtained T-DNA insertion Arabidopsis mutants at the AtGolS1 gene, an ortholog of the CsGolS1 gene. The T-DNA insertion mutant compromised resistance induced by the O6 colonization against Erwinia carotovora. Pharmaceutical application of 0.5 - 5 mM galactinol on roots was sufficient to elicit ISR in wild-type Arabidopsis against infection with E. carotovora. The involvement of jasmonic acid (JA) signaling on the ISR was validated to detect increased expression of the indicator gene PDF1.2. The T-DNA insertion mutant also compromised tolerance by increasing galactinol content in the O6-colonized plant against drought or high salt stresses. Taken together, our results indicate that primed expression of the galactinol synthase gene AtGolS1in the O6-colonized plants can play a critical role in the ISR against infection with E. carotovora, and in the tolerance to drought or high salt stresses.

• Journal of Plant Biotechnology
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• v.43 no.1
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• pp.99-103
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• 2016

In perennial ginseng plantations, the effective control of various diseases is one of the most critical factors for increasing yields. Enhancing the resistance to disease through induced systemic resistance (ISR) and anti-microbial activity of beneficial soil bacteria, is currently considered to be a potential promising approach to integrate pathogen management for sustainable agriculture. However, the effective in vitro culture systems for testing ISR in ginseng plants have been rarely reported. In this study, I have successfully developed an in vitro germ-free culture system of Panax ginseng seedling for diverse purposes. With this useful system, we also tested BTH-induced priming effects against Botrytis cinerea and Colletotrichum panacicola. Compared to the drain method for enhancing ISR effects to ginseng seedlings, the direct method of spraying leaves somewhat increased the defense activity to these major fungal pathogens. Consistently, the expression of pathogen related PgPR10 and PgCAT were greatly and rapidly enhanced in the BTH-treated ginseng seedlings by treatment with C. panacicola. Our results revealed that the in vitro culture system can be used for developing eco-friendly and versatile bio-control agents for harmful diseases in ginseng cultivation.

• The Plant Pathology Journal
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• v.29 no.2
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• pp.136-143
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• 2013

Microbial communities that are associated with plant roots are highly diverse and harbor tens of thousands of species. This so-called microbiome controls plant health through several mechanisms including the suppression of infectious diseases, which is especially prominent in disease suppressive soils. The mechanisms implicated in disease suppression include competition for nutrients, antibiosis, and induced systemic resistance (ISR). For many biological control agents ISR has been recognized as the mechanism that at least partly explains disease suppression. Implications of ISR on recruitment and functioning of the rhizosphere microbiome are discussed.

• The Plant Pathology Journal
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• v.29 no.2
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• pp.182-192
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• 2013

Numerous root-associated bacteria (rhizobacteria) are known to elicit induced systemic resistance (ISR) in plants. Bacterial cell-density-dependent quorum sensing (QS) is thought to be important for ISR. Here, we investigated the role of QS in the ISR elicited by the rhizobacterium, Serratia marcescens strain 90-166, in tobacco. Since S. marcescens 90-166 produces at least three QS signals, QS-mediated ISR in strain 90-166 has been difficult to understand. Therefore, we investigated the ISR capacity of two transgenic tobacco (Nicotiana tabacum) plants that contained either bacterial acylhomoserine lactone-producing (AHL) or -degrading (AiiA) genes in conjunction with S. marcescens 90-166 to induce resistance against bacterial and viral pathogens. Root application of S. marcescens 90-166 increased ISR to the bacterial pathogens, Pectobacterium carotovorum subsp. carotovorum and Pseudomonas syringae pv. tabaci, in AHL plants and decreased ISR in AiiA plants. In contrast, ISR to Cucumber mosaic virus was reduced in AHL plants treated with S. marcescens 90-166 but enhanced in AiiA plants. Taken together, these data indicate that QS-dependent ISR is elicited by S. marcescens 90-166 in a pathogen-dependent manner. This study provides insight into QS-dependent ISR in tobacco elicited by S. marcescens 90-166.

• Korean Journal of Environmental Biology
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• v.38 no.4
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• pp.724-732
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• 2020

Phytophthora capsici is the organism that causes Phytophthora blight which infects red pepper plants prolifically, ultimately leading to crop loss. A previous study revealed that Enterobacter asburiae ObRS-5 suppresses Phytophthora blight in both red pepper and Ligularia fischeri plants. In order to determine whether the induced systemic resistance (ISR) was triggered by pre-infection with the ObRS-5 strain, we conducted quantitative PCR using primers for PR1, PR4, and PR10, which correlate with systemic resistance in red-pepper plants. In our results, red pepper plants treated with the ObRS-5 strain demonstrated increased expression of all three systemic resistance genes when compared to controls in the glasshouse seedling assay. In addition, treatment of red peppers with the ObRS-5 strain led to reduced Phytophthora blight symptoms caused by P. capsici, whereas all control seedlings were severely affected. Perhaps most importantly, E. asburiae ObRS-5 was shown to induce the ISR response in red peppers without inhibiting growth. These results support that the defense mechanisms are triggered by ObRS-5 strain prior to infection by P. capsici and ObRS-5 strain-mediated ISR action are linked events for protection to Phytophthora blight.

• The Plant Pathology Journal
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• v.22 no.4
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• pp.360-363
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• 2006

Efficacy of plant growth promoting rhizobacteria(PGPR) Bacillus vallismortis strain EXTN-1 has been proved in eliciting induced systemic resistance(ISR) in several crops. The present paper described the beneficial effects of EXTN-1 in potato as increase in yield and chlorophyll content, and plant protection against Potato Virus Y and X(PVY & PVX). EXTN-1 induced systemic resistance to the plants resulting in significant disease suppression in the field. Also the plants under treatment with EXTN-1 had higher chlorophyll content. The bacterized plants had significantly higher yields over the untreated control plants. The strain induced activation of defense genes, PR-1a and PDF 1.2 in transgenic tobacco model, which indicated the possible role of both SA, and JA pathways in EXTN-1 mediated plant protection against crop diseases.