Accumulation Of PR Proteins Research Articles

Biocontrol Effect of Clonostachys rosea on Fusarium graminearum Infection and Mycotoxin Detoxification in Oat (Avena sativa).

Oat (Avena sativa) is susceptible to Fusarium head blight (FHB). The quality of oat grain is threatened by the accumulation of mycotoxins, particularly the trichothecene deoxynivalenol (DON), which also acts as a virulence factor for the main pathogen Fusarium graminearum. The plant can defend itself, e.g., by DON detoxification by UGT-glycosyltransferases (UTGs) and accumulation of PR-proteins, even though these mechanisms do not deliver effective levels of resistance. We studied the ability of the fungal biocontrol agent (BCA) Clonostachys rosea to reduce FHB and mycotoxin accumulation. Greenhouse trials showed that C. rosea-inoculation of oat spikelets at anthesis 3 days prior to F. graminearum inoculation reduced both the amount of Fusarium DNA (79%) and DON level (80%) in mature oat kernels substantially. DON applied to C. rosea-treated spikelets resulted in higher conversion of DON to DON-3-Glc than in mock treated plants. Moreover, there was a significant enhancement of expression of two oat UGT-glycosyltransferase genes in C. rosea-treated oat. In addition, C. rosea treatment activated expression of genes encoding four PR-proteins and a WRKY23-like transcription factor, suggesting that C. rosea may induce resistance in oat. Thus, C. rosea IK726 has strong potential to be used as a BCA against FHB in oat as it inhibits F. graminearum infection effectively, whilst detoxifying DON mycotoxin rapidly.

Differential regulation of the durum wheat Pathogenesis-related protein (PR1) by Calmodulin TdCaM1.3 protein.

In plants, pathogenesis-related 1 protein (PR1) is considered as important defense protein. The production and accumulation of PR proteins in plants are one of the important responses to several biotic and abiotic stresses. In this regard, PR1 gene was isolated from Triticum turgidum ssp durum and was named as TdPR1.2. The amino acid sequence of TdPR1.2 protein showed 100%, 97.13%, and 44.41% with known PR1 proteins isolated from Triticum aestivum TdPR1-18, PRB1.2 of Aegilops tauschii subsp. tauschii and Arabidopsis thaliana respectively. qRT-PCR showed that TdPR1.2 was induced specially in leaves of durum wheat treated with Salicylic acid for 48h. Besides, bioinformatic analysis showed that the durum wheat TdPR1.2 harbors a calmodulin binding domain located in it's C-terminal part and that this domain is conserved among different PR1 proteins isolated so far. However, no information is available about the regulation of PR genes by calmodulin and Ca2+ complex (CaM/Ca2+). Here, we showed that TdPR1.2 gene exhibits an antibacterial effect as revealed by the in vitro tests against 8 different bacteria and against the fungi Septoria tritici. In addition, we demonstrate for the first time that PR1 proteins are able to bind to CaM in a Ca2+-dependent manner via a GST-Pull down assay. Finally, in presence of Mn2+ cations, CaM/Ca2+ complex stimulated the antimicrobial effect of TdPR1.2. Such effects were not reported so far, and raise a possible role for CaM/Ca2+ complex in the regulation of plant PRs during cellular response to external signals.

Defense Gene Expression of Vigna radiata (L.) Wilczek., against Cercospora Leaf Spots (CLS)

Most cultivars of Vigna radiata (L) Wilczek grown in Indian subcontinent are susceptible to various biotic and abiotic stresses. Cercospora leaf spot (CLS) is a major biotic stress resulting in poor yield of this crop. Therefore, it is essential to investigate resistance status of different cultivars to CLS and develop effective strategy. Present investigation was focused on the role of biochemical compounds in resistance response of this crop to CLS in naturally grown population and after artificial induction with pathogen derived elicitor. The defense responses in vivo and in vitro were analyzed in the form of phytoalexin genestein, PAL and PR- proteins in their leaves. PR-proteins, PAL and genestein were assayed employing established protocols. In naturally grown population, four cultivars- Kopergaon, TARM-1, TARM-2 and TARM-18 showed lesser accumulation of genestein and lower level of PAL and PR- proteins. However, Pant M-3, ML-1037 and ML-936 showed resistant interaction with very high accumulation of genestein, PAL and PR proteins. Similar trends of accumulation of these biochemicals were observed in in vitro condition after elicitation with pathogen derived elicitor. The correlation study showed that the cultivars with lower defense related expression showed high disease incidence (51-61%) and with higher defense related expression were with less than 5% CLS incidence. It could be stated that PR-proteins, PAL and genestein has prominent role in defense mechanism of mungbean against CLS as biochemical markers and further their utility in early screening for disease resistance of crop plants could be explored.

Linking Jasmonic Acid to Grapevine Resistance against the Biotrophic Oomycete Plasmopara viticola.

Plant resistance to biotrophic pathogens is classically believed to be mediated through salicylic acid (SA) signaling leading to hypersensitive response followed by the establishment of Systemic Acquired Resistance. Jasmonic acid (JA) signaling has extensively been associated to the defense against necrotrophic pathogens and insects inducing the accumulation of secondary metabolites and PR proteins. Moreover, it is believed that plants infected with biotrophic fungi suppress JA-mediated responses. However, recent evidences have shown that certain biotrophic fungal species also trigger the activation of JA-mediated responses, suggesting a new role for JA in the defense against fungal biotrophs. Plasmopara viticola is a biotrophic oomycete responsible for the grapevine downy mildew, one of the most important diseases in viticulture. In this perspective, we show recent evidences of JA participation in grapevine resistance against P. viticola, outlining the hypothesis of JA involvement in the establishment of an incompatible interaction with this biotroph. We also show that in the first hours after P. viticola inoculation the levels of OPDA, JA, JA-Ile, and SA increase together with an increase of expression of genes associated to JA and SA signaling pathways. Our data suggests that, on the first hours after P. viticola inoculation, JA signaling pathway is activated and the outcomes of JA–SA interactions may be tailored in the defense response against this biotrophic pathogen.

Proteome and transcript analysis of Vitis vinifera cell cultures subjected to Botrytis cinerea infection.

Although gray mold caused by Botrytis cinerea is one of the most important diseases of grapevine, little information is available about proteomic changes in this pathosystem. These results suggest that cell wall strengthening, accumulation of PR proteins and excretion of lytic enzymes are important molecular mechanisms in the defence of grapevine against B. cinerea. Surprisingly, the proteins related to cell wall modification that were modulated by B. cinerea have not been shown to be affected by any other pathogen studied to date.

Proteomics and transcriptomics of the BABA-induced resistance response in potato using a novel functional annotation approach.

BackgroundInduced resistance (IR) can be part of a sustainable plant protection strategy against important plant diseases. β-aminobutyric acid (BABA) can induce resistance in a wide range of plants against several types of pathogens, including potato infected with Phytophthora infestans. However, the molecular mechanisms behind this are unclear and seem to be dependent on the system studied. To elucidate the defence responses activated by BABA in potato, a genome-wide transcript microarray analysis in combination with label-free quantitative proteomics analysis of the apoplast secretome were performed two days after treatment of the leaf canopy with BABA at two concentrations, 1 and 10 mM.ResultsOver 5000 transcripts were differentially expressed and over 90 secretome proteins changed in abundance indicating a massive activation of defence mechanisms with 10 mM BABA, the concentration effective against late blight disease. To aid analysis, we present a more comprehensive functional annotation of the microarray probes and gene models by retrieving information from orthologous gene families across 26 sequenced plant genomes. The new annotation provided GO terms to 8616 previously un-annotated probes.ConclusionsBABA at 10 mM affected several processes related to plant hormones and amino acid metabolism. A major accumulation of PR proteins was also evident, and in the mevalonate pathway, genes involved in sterol biosynthesis were down-regulated, whereas several enzymes involved in the sesquiterpene phytoalexin biosynthesis were up-regulated. Interestingly, abscisic acid (ABA) responsive genes were not as clearly regulated by BABA in potato as previously reported in Arabidopsis. Together these findings provide candidates and markers for improved resistance in potato, one of the most important crops in the world.

PR-Proteins Accumulation in Tomato Plant Due to Application of Resistance Inducing Chemicals During Period of Induced Resistance Against Alternaria Leaf Blight

Background: Resistance Inducing Chemicals (RIC) viz., Salicylic Acid (SA), $-aminobutyric acid (BABA), chitosan (CHT) and 2, 6-dichloroisonicotinic acid (INA) are known to play an important role in induction of resistance by increasing the activity of PR-proteins. Therefore the study was done to test these RIC’s for accumulation of PR-proteins in tomato plant to confer resistance against Alternaria blight disease. Methods: The activity of PR-proteins viz., chitinase and $ 1,3-glucanase in tomato leaves were measured in response to treatment of these RIC’s at different concentrations as seed dip treatment for 8 h, seedling dip treatment for 2 h and seed+seedling treatment. The RIC treated plants were challenged inoculated with Alternaria alternata, a tomato leaf blight pathogen at 10 days interval from germination and observed for disease development. Chitinases and $ 1,3-glucanase activity was determined spectronically by quantifying the release of mg of N-acetylglucosamine and of glucose, respectively at 30 days of RIC treatment as the persistence of resistance induced by RIC was up to 50 days. Results: Maximum activity of chitinase and $ 1,3-glucanase was observed in seed+seedling treatment with BABA at 15 mM concentration and the increase in chitinase and $ 1,3-glucanase activity was 32.00 and 56.59% more, respectively over control and was followed by treatment with salicylic acid at 1.5 mM concentration. Conclusion: The application of RIC SA and BABA elicits the increased activity of PR-proteins viz., chitinase and $ 1,3-glucanase which inhibit the process of pathogenesis in susceptible tomato cultivars to exhibit the resistance.

Immunohisto- and cytochemical localization of PR-10 proteins induced by heavy metals in lupine roots

Most of the data concerning PR-10 proteins accumulation in plants under various environmental stress conditions are derived from biochemical analysis of transcript expression or polypeptide accumulation. In the current study, we examined the localization of PR (L1–L6) proteins, belonging to the PR-10 class family, in the root tips of yellow lupine seedlings using histo- and cytochemical methods. Immunohistochemical localization revealed the presence of PR-proteins in all examined yellow lupine root tip tissue, and lead treatment did not change the distribution of proteins in the roots. However, the metal induced a significant increase in the accumulation of PR-proteins in the meristematic cells and procambium tissue. An immunocytochemical approach with immunogold method demonstrated the cytoplasmic nature of the PR-proteins and their increased accumulation after copper treatment. The results confirmed the affiliation of PR (L1–L6) to PR-10 class family proteins, as well as their intracellular localization.

Differential expression of pathogenesis-related proteins and defense enzymes in banana: interaction between endophytic bacteria, Banana bunchy top virus and Pentalonia nigronervosa

Banana bunchy top disease caused by Banana bunchy top virus is the most serious viral disease of banana and plantain worldwide. The virus is transmitted by the aphid vector Pentalonia nigronervosa in a persistent manner. This paper deals with the effect of the interaction between plant growth promoting endophytic bacteria, Banana bunchy top virus, and the banana aphid Pentalonia nigronervosa in the expression of Pathogenesis-related proteins (PR-proteins) and defense enzymes in banana. The existence of virus in the aphids was confirmed by ELISA, DIBA and PCR. PCR could amplify 1100-bp replicase gene of BBTV from viruliferous aphids. A significant increase in the enzymatic activity of all measured PR proteins and defense enzymes, as compared to control plants, was seen in the plants inoculated with endophytic bacteria and challenged with viruliferous aphids. Native gel electrophoresis revealed expression of more isoforms of PR proteins viz., peroxidase and chitinase in the banana plants challenged with mixtures of plant growth promoting endophytic bacteria and viruliferous aphids. Enhanced activity of a PR-2 protein viz., β-1,3-glucanase was also noticed in the viruliferous aphids infested plants. Some of the defense-related enzymes viz., Polyphenol oxidase and Phenylalanine ammonia lyase and phenolic compounds were also upregulated, up to 5 days after aphid infestation and thereafter there was a reduction in the enzymatic activity. Thus, there exist a differential accumulation of PR proteins and defense-related enzymes, when there is tri-tropic interaction between endophytic bacteria, virus, and insect and the role of the endophytic bacteria in the defense mechanisms against insect pests needs to be elucidated.

Plant growth promoting rhizobacterial (PGPR) bioconsortia mediates induction of defense-related proteins against infection of root rot pathogen in mulberry plants

The mixture of Pseudomonas fluorescens isolate Pf1 and Py15 and Bacillus subtilis isolate 16 (Bs16) was found to protect mulberry plants from root rot disease caused by Macrophomina phaseolina. Induction of defense-related proteins and chemicals by the mixture of Pf1, Py15 and Bs16 against challenge inoculation with M. phaseolina in mulberry were studied. The activity of defense enzymes peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), β-1, 3-glucanase, chitinase and defense chemical total phenols were found to be significantly higher in combined application of biocontrol agents Pf1+Py15+Bs16 followed by Pf1+Bs16, Pf1+Py15 and Py15+Bs16 treated plants when compared to individual treatments and control. The SDS-PAGE analysis of protein in biocontrol agents treated plant showed eight proteins with molecular weight of 14, 23, 30, 35, 45, 50, 60 and 98 kDa. In healthy plants only six proteins (excepting 14 and 98 kDa) appeared in biocontrol agents treated plant two additional new proteins appeared. These results suggest that induction of defense enzymes involved in phenyl propanoid pathway and accumulation of total phenols and PR-proteins might have contributed to restriction of invasion of M. phaseolina in mulberry roots.

Comparative analysis of PR gene expression in tomato inoculated with virulent Fusarium oxysporum f. sp. lycopersici and the biocontrol strain F. oxysporum Fo47

Non-pathogenic strains of Fusarium oxysporum have the capacity to protect plants against wilt induced by pathogenic strains of F. oxysporum. Among the mechanisms involved in this protection, induced systemic resistance has been demonstrated by using a split-root method. The aim of this study was to follow the accumulation kinetics of transcripts encoding 5 PR proteins in roots and leaves of tomato inoculated with a pathogenic or a protective strain in comparison to non-inoculated control. Moreover quantification of transcripts was assessed by real-time RT-PCR in cell cultures inoculated with the pathogenic or the protective strain. Results showed a lower expression of PR encoding genes in the plants or cells inoculated with the protective strain. These results showing that there is no increased accumulation of PR proteins after inoculation of the protective strain, suggest that accumulation could follow inoculation of the pathogen. Priming the plant defense reaction could be the mode of action of Fo47.

Endophytic Pseudomonas fluorescens Endo2 and Endo35 induce resistance in black gram (Vigna mungo L. Hepper) to the pathogen Macrophomina phaseolina

The effect of endophytic Pseudomonas fluorescens isolates Endo2 and Endo35 on induced systemic disease protection against dry root rot of black gram (Vigna mungo L. Hepper) caused by Macrophomina phaseolina was investigated under glasshouse conditions. When the bacterized black gram plants were inoculated with dry root rot pathogen, the activities of peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL) were stimulated in addition to accumulation of phenolics and lignin. Activity of phenylalanine ammonia-lyase (PAL) reached the maximum 24 h after pathogen challenge inoculation, whereas the activities of PO and PPO reached the maximum at 72 h and 48 h, respectively. Isoform analysis revealed that a unique PPO3 isozyme was induced in bacterized black gram tissues inoculated with the pathogen. Phenolics were found to accumulate in bacterized black gram tissues challenged with M. phaseolina one day after pathogen challenge. The accumulation of phenolics reached maximum at the third day after pathogen inoculation. Similar observation was found in the lignin content of black gram plants. In untreated control plants, the accumulation of defence enzymes and chemicals started at the first day and drastically decreased 3 days after pathogen inoculation. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restricting invasion of Macrophomina phaseolina in black gram roots.

Molecular defense responses of apple genotypes in compatible and incompatible interactions with Erwinia amylovora

Erwinia amylovora is the causal agent of fire blight, a bacterial disease of apple and pear. Pathogenicity determinants of the bacteria are identified (hrp-dsp cluster, capsule, siderophore) but molecular mechanisms leading to susceptibility or resistance of the plant are not yet understood. To address this question, we challenged two genotypes of apple, known for their contrasting susceptibility to fire blight, with a wild-type strain of E. amylovora (Ea wt), an avirulent hrp mutant of this bacteria (Ea hrp) or a wild-type strain of the incompatible pathogen Pseudomonas syringae pv. tabaci (Pst wt). Mechanisms usually related to resistance responses were investigated i.e. oxidative stress, accumulation of PR-proteins and induction of genes encoding various enzymes of the phenylpropanoid pathway. Results showed two kinds of responses (i) some mechanisms were elicited in both susceptible and resistant genotypes by Ea wt and Pst wt with similar kinetics and not induced by Ea hrp, (ii) others were specifically repressed by Ea wt in its susceptible host, when induced by Pst wt and Ea hrp. These results suggest several hypothesis about the cross-talk between E. amylovora and its host plants.

Induction of defense-related proteins in tomato roots treated with Pseudomonas fluorescens Pf1 and Fusarium oxysporum f. sp. lycopersici

Pseudomonas fluorescens isolate Pf1 was found to protect tomato plants from wilt disease caused by Fusarium oxysporum f. sp. lycopersici. Induction of defense proteins and chemicals by P. fluorescens isolate Pf1 against challenge inoculation with F. oxysporum f. sp. lycopersici in tomato was studied. Phenolics were found to accumulate in bacterized tomato root tissues challenged with F. oxysporum f. sp. lycopersici at one day after pathogen challenge. The accumulation of phenolics reached maximum at the 5th day after pathogen challenge. In pathogen-inoculated plants, the accumulation started at the 2nd day and drastically decreased 4 days after the pathogen inoculation. Activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) increased in bacterized tomato root tissues challenged with the pathogen at one day after pathogen challenge and activities of PAL and PO reached maximum at the 4th day while activity of PPO reached maximum at the 5th day after challenge inoculation. Isoform analysis revealed that a unique PPO1 isoform was induced and PO1 and PPO2 isoforms were expressed at higher levels in bacterized tomato root tissues challenge inoculated with the pathogen. Similarly, β-1,3 glucanase, chitinase and thaumatin-like proteins (TLP) were induced to accumulate at higher levels at 3-5 days of challenge inoculation in bacterized plants. Western blot analysis showed that chitinase isoform Chi2 with a molecular weight of 46 kDa was newly induced due to P. fluorescens isolate Pf1 treatment challenged with the pathogen. TLP isoform with molecular weight of 33 kDa was induced not only in P. fluorescens isolate Pf1-treated root tissues challenged with the pathogen but also in roots treated with P. fluorescens isolate Pf1 alone and roots inoculated with the pathogen. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restriction of invasion of F. oxysporum f. sp. lycopersici in tomato roots.

PR Protein Accumulation in Seminal Roots of Barley and Wheat in Response to Fungal Infection ‐ the Importance of Cortex Senescence

AbstractThe accumulation of PR proteins in the roots of barley and wheat was investigated in response to root infection with the necrotrophic pathogen Bipolaris sorokiniana. Analyses of protein extracts using both biochemical methods and immunohistological localization on tissue sections were performed. Several PR proteins, particularly PR‐1 and PR‐5, accumulated in response to infection. The pattern was similar to that observed in earlier reports after infection with, for example, Blumeria graminis and Drechslera teres. Leaf tissue from root‐inoculated plants were also analysed and it was found that isoforms of PR‐3 and PR‐5 proteins were differently expressed in leaves and roots, indicating tissue‐specific expression. Tissue differences were observed within the roots as PR‐3 proteins was constitutively expressed in the root cortex but not in the stele. PR protein accumulation in the leaves after root inoculation indicate systemic induction. Evidence was also found for systemic induction within the roots as PR proteins accumulated in root tissues that were distant from the infection point. Infection of roots close to the root tip caused a stronger accumulation of PR proteins compared with infection of older segments of seminal roots. This was particularly evident in wheat where almost no effect of inoculation of older root segments could be detected. The patterns of PR protein accumulation in seminal roots are discussed in relation to root cortical cell death, a phenomenon that has earlier been found to occur at a progressively increasing rate from the root tip and upwards.

PR Protein Accumulation in Seminal Roots of Barley and Wheat in Response to Fungal Infection - the Importance of Cortex Senescence

PR Protein Accumulation in Seminal Roots of Barley and Wheat in Response to Fungal Infection - the Importance of Cortex Senescence

Elicitation of peroxidase activity and lignin biosynthesis in pepper suspension cells by Phytophthora capsici

Summary Cell suspension cultures of three varieties of Capsicum annuum L., each with a different degree of sensitivity to the fungus Phytophthora capsici, responded to elicitation by both lyophilized mycelium and fungus filtrate with a hypersensitive reaction. They showed the synthesis or accumulation of PR-proteins with peroxidase (EC 1.11.1.7) activity and the accumulation of lignin-like polymer (as measured by derivatization with thioglycolic acid). The cultivation medium was optimised for both plant and fungus growth in order to avoid any stress during their combination. The resistant pepper variety, Smith-5, showed a more intense response to the elicitor preparations than the sensitive varieties, Americano and Yolo Wonder. This was particularly evident when the cell suspensions were elicited with the filtrate. After elicitation, the cell walls thickened through the accumulation of lignin, as can be observed by staining microscope preparations with methylene blue. Elicitation also reduced the level of total peroxidase activity in the susceptible varieties, while such activity increased in resistant varieties, and was accompanied by de novo expression of acidic peroxidase isoenzymes in the extracellular and cell wall fractions. Of note was the PR protein of pI 5.7 showing peroxidase activity, which was induced by both elicitor types in the elicited cell suspensions of the resistant variety alone, making it a marker of resistance. The increases in the activity of these peroxidases in the resistant variety are in concordance with the accumulation of lignin observed 24 h after inoculation by both elicitors from the fungus. The possible role of these isoenzymes in lignin biosynthesis, used to reinforce the cell walls against fungal penetration of the cells, is discussed. These results are in accordance with those previously observed in plant stem sections.

Constitutive hydrolytic enzymes are associated with polygenic resistance of tomato to Alternaria solani and may function as an elicitor release mechanism

Foliar resistance to early blight disease of tomato, caused by the necrotrophic fungus Alternaria solani, is inherited in a complex quantitative manner. Our previous studies revealed that three moderately-resistant tomato breeding lines with different sources of early blight resistance, all possessed higher constitutive and more rapid accumulation of PR proteins, including specific antifungal isozymes of chitinase and β-1,3-glucanase than susceptible genotypes. In the present study, additional early blight resistant tomato breeding lines and susceptible genotypes were investigated for their constitutive levels of PR proteins. All resistant lines possessed higher constitutive levels of chitinase and β-1,3-glucanase than susceptible genotypes supporting earlier reported findings. Constitutive and pathogen-induced expression of PR genes during early stages of the interaction was found to be much higher in the highly resistant breeding line NC 24-E than a susceptible line.In vitro elicitor release experiments were performed with purified A. solani cell walls treated with constitutive total enzyme preparations isolated from resistant and susceptible plants. Enzyme preparations from resistant and susceptible genotypes differed in their ability to produce hypersensitive response (HR) elicitors from fungal cell walls: the enzyme preparations from resistant breeding lines released HR elicitors, while enzyme preparations from susceptible lines did not. Additionally, experiments with a partially purified preparation of basic tomato chitinases demonstrated that these enzymes were able to release HR elicitors from germinating spores of A. solani, but not mature, intact cell walls. The possibility that constitutively produced hydrolytic enzymes may act as an elicitor-releasing mechanism in resistance to early blight of tomato is discussed.

Induction of Pathogenesis-Related Proteins of Group 1 by Systemic Virus Infections of Nicotiana tabacum L.

Abstract The induction of acid pathogenesis-related proteins (PR-proteins) of group 1 (PR-1) by systemic virus infections of tobacco plants was investigated during a time period between 3 and 19 days after inoculation. Each leaf position was investigated separately. The PR proteins were detected electrophoretically and, in addition, virus protein was detected by Enzyme Linked Immunosorbent Assay (ELISA). Potato virus X (PVX) and potato virus Y (PVY) were found to highly induce PR proteins in N. tabacum L. “Samsun NN”. The same results were obtained when PVX was investigated in N. tabacum L. “Samsun”. The accumulation started later and took place more slowly than during hypersensitive host reaction (HR) of “Samsun NN” to tobacco mosaic virus (TMV). A correlation was found between the accumulation of PR proteins and the accumulation of the virus in the same leaf. Cucumber mosaic virus (CMV) was less effective in PR protein induction than PVX and PVY. Consequently it could be demonstrated that PR proteins do not only appear due to hypersensitive host reactions but also during systemic virus infections.

Induction of pathogen resistance and pathogenesis‐related genes in tobacco by a heat‐stable Trichoderma mycelial extract and plant signal messengers

Heat‐stable mycelial extracts of the nonpathogenic fungus Trichoderma longibrachiatum induced resistance in tobacco seedlings (Nicotiana tabacum L. cv. Wisconsin 38) to the pathogen Phytophthora parasitica var. nicotianae (race 0), which did not involve a hypersensitive response. Resistance could not be induced with mycelial extract prepared in the same manner from P. parasitica. The nonpathogenic mycelial extract induced expression of PR‐1b and osmotin (PR‐5) genes to a higher level than did mycelial extract from the pathogenic fungus. The tissue‐specific pattern of PR gene induction by the nonpathogenic mycelial extract was different from that of the pathogenic mycelial extract and was consistent with the ability of the former to cause disease resistance. The expression patterns of these two PR genes and the accumulations of their encoded proteins also were affected by salicylic acid (SA), methyl jasmonate (MeJA), ethylene (E) and combinations of these plant signal messengers. However, only combined SA and MeJA treatment mimicked the pattern of PR gene mRNA and protein accumulation induced by the nonpathogenic mycelial extract. E inhibitors blocked both mycelial extract‐induced and SA/MeJA‐induced PR gene expression, and the cis pattern of responsiveness on the osmotin promoter was the same for the mycelial extract, SA, E, or E/MeJA. Seedlings treated with P. parasitica spores in the presence of SA/MeJA were protected from pathogen colonization. However, these seedlings exhibited symptoms of cell death (disease symptoms) both in the absence and presence of P. parasitica spores, in contrast to seedlings treated with nonpathogenic mycelial extract, which remained healthy. These results suggest that the signal transduction pathways for elicitation of defense responses by exogenously applied heat‐stable nonpathogenic mycelial extract and SA/MeJA overlap at the point of PR protein induction but are not identical.