Pathogenesis-related Gene 1 Expression Research Articles

Hydrogen peroxide regulated salicylic acid– and jasmonic acid–dependent systemic defenses in tomato seedlings

To investigate the regulation of hydrogen peroxide (H2O2) in SA- and JA-dependent systemic defense pathways in tomato seedlings damaged by cotton bollworm. The lower two leaves of four-leaf tomato plant seedlings were treated with cotton bollworms. The upper leaves were then removed at various time points and assessed for systemic changes in H2O2 levels, enzyme activity and defense-related genes expression. Wild-type seedlings, def-5 mutant seedlings (deficient in JA accumulation) and transgenic nahG seedlings(deficient in SA content) were constructed at four-leaf stage. Wild-type plants were further treated with dimethylthiourea (DMTU) and 2,5-dihydroxycinnamic acid methyl ester (DHC). Bollworm feeding in the lower leaves induced rapid systemic accumulation of H2O2 in the upper leaves. H2O2 accumulation further increased activities for SA- and JA-dependent enzymes including proteinase inhibitors (PIs), pathogenesis-related gene 1 (PR-1), cathepsin D inhibitor (CDI), β-1,3-glucanse (BGL) and polyphenol oxidase (PPO). Furthermore, H2O2 accumulation enhanced mRNA expression of BGL-2, PR-1, PI, CDI and PPO genes. Suppression of H2O2 accumulation using H2O2 scavengers substantially diminished these effects. mRNA expression of PR-1 was not induced in transgenic nahG plants. SA- and JA-dependent signaling pathways are involved in the tomato systemic defense responses to herbivores, and that H2O2 generation is required for both systemic pathways.

ELF18-INDUCED LONG NONCODING RNA1 evicts fibrillarin from mediator subunit to enhance PATHOGENESIS-RELATED GENE1 (PR1) expression.

Plant immune response is initiated upon the recognition of pathogen-associated molecular patterns such as elf18. Previously, we identified an Arabidopsis ELF18-INDUCED LONG NONCODING RNA1 (ELENA1), as a positive transcriptional regulator of immune responsive genes. ELENA1 associated with Mediator subunit 19a (MED19a) to enhance enrichment of the complex on PATHOGENESIS-RELATED GENE1 (PR1) promoter. In vitro and invivo RNA-protein interaction experiments showed that ELENA1 can also interact with FIBRILLARIN2 (FIB2). Co-immunoprecipitation and bimolecular fluorescence complementation assay showed that FIB2 directly interacts with MED19a in nucleoplasm and nucleolus. Analysis of fib2 mutant showed that FIB2 functions as a negative transcriptional regulator for immune responsive genes, including PR1. Genetic and biochemical analyses demonstrated that ELENA1 can dissociate the FIB2/MED19a complex and release FIB2 from PR1 promoter to enhance PR1 expression. ELENA1 increases PR1 expression by evicting the repressor (FIB2) from the activator (MED19a). Our findings uncover an additional layer of complexity in the transcriptional regulation of plant immune responsive genes by long noncoding RNA.

Transcript analysis of some defense genes of tomato in response to host and non-host bacterial pathogens.

The transcript levels of six defense genes including pathogenesis-related gene 1 (PR-1), pathogenesis-related gene 2 (PR-2), pathogenesis-related gene 5 (PR-5), lipoxygenase (LOX), phenylalanine ammonia-lyase (PAL) and catalase (CAT) were investigated in tomato plants inoculated with Xanthomonas axonopodis pv. phaseoli as a non-host pathogen and X. euvesicatoria as a host pathogen. Activation of all the genes was confirmed in both host and non-host treatments. Additionally, the results showed stronger expression of majority of the genes (PR-1, PR-2, LOX, PAL and CAT) in non-host treatment compared to host treatment at least at early hours after inoculation. These data suggest that faster and more expression of PR-1, PR-2, LOX, PAL and CAT might have a role in non-host resistance of tomato against X. axonopodis pv. phaseoli.

ELF18-INDUCED LONG-NONCODING RNA Associates with Mediator to Enhance Expression of Innate Immune Response Genes in Arabidopsis.

The plant immune response is a complex process involving transcriptional and posttranscriptional regulation of gene expression. Responses to plant immunity are initiated upon the perception of pathogen-associated molecular patterns, including peptide fragment of bacterial flagellin (flg22) or translation elongation factor Tu (elf18). Here, we identify an Arabidopsis thaliana long-noncoding RNA, designated ELF18-INDUCED LONG-NONCODING RNA1 (ELENA1), as a factor enhancing resistance against Pseudomonas syringe pv tomato DC3000. ELENA1 knockdown plants show decreased expression of PATHOGENESIS-RELATED GENE1 (PR1) and the plants are susceptible to pathogens. By contrast, plants overexpressing ELENA1 show elevated PR1 expression after elf18 treatment and display a pathogen resistance phenotype. RNA-sequencing analysis of ELENA1-overexpressing plants after elf18 treatment confirms increased expression of defense-related genes compared with the wild type. ELENA1 directly interacts with Mediator subunit 19a (MED19a) and affects enrichment of MED19a on the PR1 promoter. These results show that MED19a regulates PR1 expression through ELENA1. Our findings uncover an additional layer of complexity, implicating long-noncoding RNAs in the transcriptional regulation of plant innate immunity.

A wheat COP9 subunit 5-like gene is negatively involved in host response to leaf rust.

SummaryThe COP9 (constitutive photomorphogenesis 9) signalosome (CSN) is a protein complex involved in the ubiquitin proteasome system and a common host target of diverse pathogens in Arabidopsis. The known derubylation function of the COP9 complex is carried out by subunit 5 encoded by AtCSN5A or AtCSN5B in Arabidopsis. A single CSN5‐like gene (designated as TaCSN5) with three homeologues was identified on the long arms of wheat (Triticum aestivum L.) group 2 chromosomes. In this study, we identified and characterized the function of TaCSN5 in response to infection by the leaf rust pathogen. Down‐regulation of all three TaCSN5 homeologues or mutations in the homeologues on chromosomes 2A or 2D resulted in significantly enhanced resistance to leaf rust. Enhanced leaf rust resistance corresponded to a seven‐fold increase in PR1 (pathogenesis‐related gene 1) expression. Collectively, the data indicate that the wheat COP9 subunit 5‐like gene acts as a negative regulator of wheat leaf rust resistance.

Induction of pathogenesis-related gene 1 (PR-1) by acibenzolar-s-methyl application in pineapple and its effect on reniform nematodes (Rotylenchulus reniformis)

The induction of systemic acquired resistance (SAR) in pineapples (Ananas comosus) was studied as shown by the up-regulation of the PR-1 gene (the SAR marker) and examination of the SAR effect on the reniform nematode, Rotylenchulus reniformis. Real-time polymerase chain reaction assay was performed using degenerate primers designed from the PR-1 genes of several monocotyledonous (monocots) and dicotyledonous (dicots) plants. A 266 bp cDNA band was evident only in plants treated with the SAR inducer, acibenzolar-s-methyl. This 266 bp cDNA was sequenced and found to be highly homologous to a number of PR-1 genes from monocots. In addition, the amino acid sequence deduced from the 266 bp cDNA showed a high identity to PR-1 proteins from both monocots and dicots. Therefore, it was highly likely that this cloned fragment was part of the A. comosus PR-1 gene, indicating that A. comosus has an SAR pathway. The time course of PR-1 expression was studied. The results showed that PR-1 induction was initiated as early as 1 d after acibenzolar application and continued through 3 wk thereafter. The effect of SAR on the nematodes, R. reniformis, in pineapples was also elucidated. The results showed that the reproduction of nematodes on the pineapples treated with 100 mg/L or 200 mg/L was 55% lower than that on pineapples treated with 0 mg/L or 50 mg/L. Nematode reproduction on pineapples treated with the same concentration but inoculated at different times was not significantly different (p > 0.05).

Effect of β-aminobutyric acid on resistance of tomato against Pectobacterium carotovorum subsp. carotovorum

Stem rot of tomato caused by Pectobacterium carotovorum subsp. carotovorum (Pcc) results in economic yield loss worldwide. Previous studies have demonstrated the role of β-aminobutyric acid (BABA) in control of numerous plant diseases. To extend our understanding for the efficacy of BABA as an inducer agent against plant diseases, we evaluated the effect of BABA on disease severity of stem rot during infection of tomato by Pcc. BABA at concentration of 200 µM reduced the disease severity and offered protection against Pcc. On the other hand, BABA did not have direct antibacterial effect in vitro. Furthermore, we examined the effects of BABA on expression of pathogenesis-related gene 1 (PR-1), pathogenesis-related gene 2 (PR-2), phenylalanine ammonia-lyase (PAL) and catalase (CAT). Pretreatment with BABA led to more expression of PR-1 and PR-2 after Pcc infection when compared with their counterparts pretreated with water (control). PR-1 expression in BABA/Pcc treatment increased 2.83-, 4.31-, 2.46- and 1.88-fold at 24, 48, 72 and 96 h postpathogen inoculation (hpi), respectively, compared to water/Pcc treatment. Moreover, PR-2 expression in BABA/Pcc treatment increased 2.66-, 3.43-, 2.19- and 1.91-fold at 24, 48, 72 and 96 hpi, respectively, compared to water/Pcc treatment. On the other hand, PAL expression was transient during enhanced resistance by BABA. In comparison with water/Pcc treatment, PAL expression enhanced 2.42-fold at 24 hpi in BABA/Pcc treatment, whereas PAL expression was remained unchanged at 48, 72 and 96 hpi. CAT expression increased in early stages of the resistance induced by BABA. In BABA/Pcc treatment, CAT expression enhanced 4.6- and 3.1-fold at 24 and 48 hpi, respectively, compared to water/Pcc treatment. Our data confirmed the role of BABA as an effective resistance inducer against Pcc that might be considered in integrated diseases management programs.

Nitrate reductase is required for the transcriptional modulation and bactericidal activity of nitric oxide during the defense response of Arabidopsis thaliana against Pseudomonas syringae

Nitrate reductase (NR) has emerged as a potential NO source in plants. Indeed, the Arabidopsis thaliana NR double-deficient mutant (nia1 nia2) produces low NO and develops abnormal susceptibility to bacterial infection. We have employed quantitative real-time polymerase chain reactions to analyze the effects of NO gas on the expression of defense-related genes in wild-type and nia1 nia2 A. thaliana plants that were inoculated with an avirulent strain of Pseudomonas syringae pv. tomato. The pathogenesis-related gene 1 (PR1) was up-regulated by bacterial infection, and its expression was higher in the wild type than in nia1 nia2. Fumigation with NO attenuated the expression of PR1 and other salicylic acid-related genes in plants that had been inoculated with P. syringae. Nevertheless, NO inhibited the most intense bacterial growth and disease symptoms in nia1 nia2 leaves. The NO fumigation also directly modulated lignin biosynthesis-related gene expression (CAD1) and parts of the auxin (TIR1, ILL1, GH3) and ethylene (ACCS7) pathways, among other defense-related genes, and their modulation was more intense in the NR-deficient mutant. Pathogen inoculation induced delayed but intense H2O2 production in mutant leaves in comparison with the wild type. Hydrogen peroxide potentiated the microbicidal effects of NO against bacterial cultures. These results suggest that NO has a direct microbicidal effect in combination with H2O2 to allow for the attenuation of the SA-mediated defense response, thereby reducing the energy expenditure associated with defense-related gene transcription. Overall, these results highlight the importance of NR-dependent NO production in the establishment of disease resistance.

Biotic stress in plants: life lessons from your parents and grandparents

Biotic stress in plants: life lessons from your parents and grandparents

3‐Acetonyl‐3‐hydroxyoxindole: a new inducer of systemic acquired resistance in plants

Systemic acquired resistance (SAR) is an inducible defence mechanism which plays a central role in protecting plants from microbial pathogen attack. Guided by bioassays, a new chemical inducer of SAR was isolated from the extracts of Strobilanthes cusia and identified to be 3-acetonyl-3-hydroxyoxindole (AHO), a derivative of isatin. Tobacco plants treated with AHO exhibited enhanced resistance to tobacco mosaic virus (TMV) and to the fungal pathogen Erysiphe cichoracearum (powdery mildew), accompanied by increased levels of pathogenesis-related gene 1 (PR-1) expression, salicylic acid (SA) accumulation and phenylalanine ammonia-lyase activity. To study the mode of action of AHO, its ability to induce PR-1 expression and TMV resistance in nahG transgenic plants expressing salicylate hydroxylase, which prevents the accumulation of SA, was analysed. AHO treatment did not induce TMV resistance or PR-1 expression in nahG transgenic plants, suggesting that AHO acts upstream of SA in the SAR signalling pathway. In addition, using two-dimensional gel electrophoresis combined with mass spectrometry, five AHO-induced plant proteins were identified which were homologous to the effector proteins with which SA interacts. Our data suggest that AHO may represent a novel class of inducer that stimulates SA-mediated defence responses.

The BOS loci of Arabidopsis are required for resistance to Botrytis cinerea infection

Three Botrytis-susceptible mutants bos2, bos3, and bos4 which define independent and novel genetic loci required for Arabidopsis resistance to Botrytis cinerea were isolated. The bos2 mutant is susceptible to B. cinerea but retains wild-type levels of resistance to other pathogens tested, indicative of a defect in a response pathway more specific to B. cinerea. The bos3 and bos4 mutants also show increased susceptibility to Alternaria brassicicola, another necrotrophic pathogen, suggesting a broader role for these loci in resistance. bos4 shows the broadest range of effects on resistance, being more susceptible to avirulent strain of Pseudomonas syringae pv. tomato. Interestingly, bos3 is more resistant than wild-type plants to virulent strains of the biotrophic pathogen Peronospora parasitica and the bacterial pathogen P. syringae pv. tomato. The Pathogenesis Related gene 1 (PR-1), a molecular marker of the salicylic acid (SA)-dependent resistance pathway, shows a wild-type pattern of expression in bos2, while in bos3 this gene was expressed at elevated levels, both constitutively and in response to pathogen challenge. In bos4 plants, PR-1 expression was reduced compared with wild type in response to B. cinerea and SA. In bos3, the mutant most susceptible to B. cinerea and with the highest expression of PR-1, removal of SA resulted in reduced PR-1 expression but no change to the B. cinerea response. Expression of the plant defensin gene PDF1-2 was generally lower in bos mutants compared with wild-type plants, with a particularly strong reduction in bos3. Production of the phytoalexin camalexin is another well-characterized plant defense response. The bos2 and bos4 mutants accumulate reduced levels of camalexin whereas bos3 accumulates significantly higher levels of camalexin than wild-type plants in response to B. cinerea. The BOS2, BOS3, and BOS4 loci may affect camalexin levels and responsiveness to ethylene and jasmonate. The three new mutants appear to mediate disease responses through mechanisms independent of the previously described BOS1 gene. Based on the differences in the phenotypes of the bos mutants, it appears that they affect different points in defense response pathways.