Jasmonate signaling in plant interactions with resistance-inducing beneficial microbes. BMC Plant Biol. Although we did not detect a large amount of SA induced in roots, it is clearly that LJ02 could significant induce its production in a temporal manner. 61, 11041109. Evaluation of the biocontrol potential of Streptomyces goshikiensis YCXU against Fusarium oxysporum f. sp niveum. Microbiol. (Figure 6C). Perception of pathogenic or beneficial bacteria and their evasion of host immunity: pattern recognition receptors in the frontline. Figure 4. During initial screening of LJ02, greenhouse trials indicated that LJ02 is effective in controlling cucurbits powdery mildew over 20 days. doi: 10.1631/jzus.B0820341, Mauch-Mani, B., and Slusarenko, A. J. We extracted the free SA and the sugar-conjugated SA from LJ02FB-treated plant leaves and monitored the trend of SA accumulation in the cucumber leaves in time-course experiments. Abscisic acid enhances resistance to Alternaria solani in tomato seedlings. Although it is similar to that described for disk diffusion method (On et al., 2015), our new method takes the advantage of the coordinate activation of anti-fungal substances by plant-BCA-pathogen interactions rather than traditional BCA-pathogen interactions. Selection of appropriate reference genes for gene expression studies by quantitative real-time polymerase chain reaction in cucumber. Figure 1. doi: 10.1016/j.biocontrol.2014.11.012, Farace, G., Fernandez, O., Jacquens, L., Coutte, F., Krier, F., Jacques, P., et al. doi: 10.1016/j.biocontrol.2014.09.017, Palva, T. K., Hurtig, M., Saindrenan, P., and Palva, E. T. (1994). Harnessing useful rhizosphere microorganisms for pathogen and pest biocontrol, View all
Actually, it was reported that PAL and PPO are the main SAR-related enzymes in plants (Jung et al., 2011). doi: 10.1094/Mpmi-7-0356, Park, S. W., Kaimoyo, E., Kumar, D., Mosher, S., and Klessig, D. F. (2007). PAL was also enhanced during LJ02 treatment. It was reported that foliar attack by the whitefly not only elicited AG resistance against a leaf pathogen, Xanthomonas axonopodis pv. A., and Chen, J. F. (2010). Acetyl salicylic acid alleviates chilling-induced damage in muskmelon seedlings. A rapid assay for catechol oxidase and lactase using 2-nitro-5-thiobenzoic acid. 6:883. doi: 10.3389/fmicb.2015.00883. Comparison of gyrB gene sequences, 16S rRNA gene sequences and DNA-DNA hybridization in the Bacillus subtilis group. doi: 10.1016/j.phytochem.2009.06.009, Verberne, M. C., Verpoorte, R., Bol, J. F., Mercado-Blanco, J., and Linthorst, H. J. 108, 16731678. Annu. Strain LJ02 produces H2S and can use citrate as sole carbon source. doi: 10.1146/annurev-phyto-073009-114447, Romero, D., De Vicente, A., Zeriouh, H., Cazorla, F. M., Fernandez-Ortuno, D., Tores, J. A one-way ANOVA was performed (*P < 0.05; **P < 0.01). (2009). Univ. Error bars indicate standard deviation among triplicates. Analysis of defence enzymes induced by antagonistic bacterium Bacillus subtilis strain AR12 towards Ralstonia solanacearum in tomato. Biotechnol. To further unravel the long-range effect of LJ02FB treatment, we tested the biocontrol activity of root exudates or secretions against common pathogenic fungi. The gyrB gene sequence of LJ02 was submitted to GenBank database and the accession number is KF501049. Moreover, the quantity of rhizosphere fungi was determined after treated with LJ02FB in cucumber leaves. Therefore, we detected the diameter of inhibition zone against other pathogen fungi (F. oxysporum, B. cinerea, and Alternaria spp.) Each pathogen fungus (F. oxysporum, B. cinerea, and Alternaria spp.) Microbiol. Although 16S rRNA sequence has been commonly used as a simple method for the identification of microorganisms, it has limitations for constructing bacterial phylogenetic relationships due to the high percentage of sequence similarity between closely related species. As is described previously, S. fuliginea is an obligate parasite which is hard to culture on nutrient medium (Perez-Garcia et al., 2009). 138, 520533. Figure 7. 42, 185209. Science 318, 113116. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Rev. (E) The comparison of the inhibition zone of cucumber rhizosphere MS solid medium against different pathogenic fungi (cm). doi: 10.1016/j.micres.2011.02.004, Korkmaz, A., Uzunlu, M., and Demirkiran, A. R. (2007). Received: 03 April 2015; Accepted: 11 August 2015; Published: 28 August 2015. Identification of a new spore wall protein from Encephalitozoon cuniculi. doi: 10.1099/ijs.0.64685-0, Wang, P., Zhang, S., Wang, C., and Lu, J. Besides, we found that the production of several resistance-related enzymes has been significantly stimulated upon LJ02 treatment, which was probably caused by the coordinate activation by enhanced SA levels in LJ02-treated plants. The results proved that strain LJ02 indeed inhibited the occurrence of cucurbits powdery mildew under greenhouse condition. (2012). doi: 10.1094/MPMI.1997.10.5.624, Trda, L., Boutrot, F., Claverie, J., Brule, D., Dorey, S., and Poinssot, B. 49, 317343. doi: 10.1093/molbev/msr121, Tornero, P., Gadea, J., Conejero, V., and Vera, P. (1997). Sci. The MS solid medium containing rhizosphere secretions was made into cake by a sterile puncher (0.5 cm in diameter). Considerable decrease in spore germination and fungal growth were detected after treated with LJ02FB. PRR-mediated microbe sensing gives rise to a wide array of defense responses known as MAMP- or PAMP-triggered immunity (MTI/PTI; Zipfel, 2014). All experiments had at least five replicates. doi: 10.1007/s00425-002-0750-4, Li, S. M., Hua, G. G., Liu, H. X., and Guo, J. H. (2008). Disease index and control efficacy of powdery mildew in cucumber. Plant Pathol. Plant Cell 8, 203212. Plant Signal. In our study, the activities of resistance-related enzymes including SOD, POD, PPO, and PAL considerably increased after treated by LJ02FB. The PAL activities of either group reached the top level at 3rd day, while treatment group induced significantly stronger PAL activity (P < 0.05) than the control at the maximum inducing time point (Figure 3D). doi: 10.1105/tpc.8.2.203, Murashige, T., and Skoog, F. (1962). (C) spores with different treatments. except 16S rRNA gene sequence (Yamamoto and Harayama, 1995). Cell Fact. After treated for 48 h, cucumber seedlings were pulled from the MS solid medium. Biocontrol 50, 165178. In order to investigate the effect of LJ02FB on this process, the expression of PR-1 in cucumber leaves was studied after treated with LJ02FB. Can. Phylogenetic analysis of LJ02 was determined using gyrB gene as a reference (Yamamoto and Harayama, 1995). doi: 10.1099/00207713-37-1-69, Ramarathnam, R., Fernando, W. G. D., and De Kievit, T. (2011). Physiological and biochemical characteristics of strain LJ02. 57, 18461850. However, the different effects of LJ02BC and LJ02FS on the SA-mediated defense responses may attributed to certain unidentified MAMP factors that functions in association with bacterium itself. Intriguingly, in our study, we detected a significant increase in the content of free SA in cucumber leaves during LJ02 treatment. A. Physiol. We found that the accumulation of free SA on cucumber leaves increased rapidly after 5-day treatment as compared to control (Figure 4C). Biocontrol 56, 225235. Microbiol. 15, 4953. Finally, we further dissect the roles played by LJ02BC and L02FS and found that LJ02 could really elicit SAR response in leaves as well as in roots. Gram staining and microscopic observation showed that LJ02 is Gram-positive, endospore-forming and rod-shaped bacterium with a width of 0.70.9 m and a length of 1.83.0 m, indicative of a typical bacillus morphology (Figure 2). Hormone crosstalk in plant disease and defense: more than just jasmonate-salicylate antagonism. J. 167, 1419. Plant Microbe Interact. doi: 10.1016/J.Ab.2009.12.008, Wang, L. T., Lee, F. L., Tai, C. J., and Kasai, H. (2007). Plant J. (D) The quantity of pathogenic fungi in the rhizosphere of cucumber treated by different concentrations of LJ02FB in leaves. 399, 257261. J. Biotechnol. Anal. Induction of defense-related enzymes in soybean leaves by class IId bacteriocins (thuricin 17 and bacthuricin F4) purified from Bacillus strains. (2007). And it appeared that LJ02BC played a major role in this process, although the amount of free SA was lower as compared to that of leaves. Specifically, strain LJ02 is aerobic and cannot grow under anaerobic conditions. One strain was selected and named LJ02. Planta 215, 239247. These are conserved signatures of crucial microbial structures, such as cell wall components or motility organs (Boller and Felix, 2009) as well as cyclic lipopeptides found in B. subtilis (Farace et al., 2015). doi: 10.1007/s10526-010-9324-8, Reuveni, M., Agapov, V., and Reuveni, R. (1996). At the first beginning, the identification of LJ02 as B. amyloliquefaciens is different from previous studies since we could not distinguish it from B. subtilis based on 16S rRNA comparison (data not shown). Therefore, it is conceivably that similar substances will be produced in its close species, B. amyloliquefaciens and similar immune responses will be induced. Based on the long-range resistance responses, we have established a method that could easily detect the inhibitory effect induced by foliar BCAs. doi: 10.1094/MPMI-19-0711, Haas, D., and Defago, G. (2005). The physiological and biochemical properties were determined and shown in Table 2. J. Syst. Science doi: 10.1126/science.aaa8764 [Epub ahead of print]. (2009). Very recently, it was discovered that SA could modulate colonization of the root microbiome by specific bacterial taxa, indicating that SA is likely to be important for the colonization or recruitment of beneficial microbes in rhizosphere (Lebeis et al., 2015). Hydrogen peroxide stimulates salicylic acid biosynthesis in tobacco. Purification and characterization of a novel antifungal protein from Bacillus subtilis strain B29. Interplay between MAMP-triggered and SA-mediated defense responses. Error bars indicate standard deviation among triplicates. 17, 155167. 6:219. doi: 10.3389/fpls.2015.00219, Tsuda, K., Sato, M., Glazebrook, J., Cohen, J. D., and Katagiri, F. (2008). Biol. Xu, G. H., and Zheng, H. Y. Biol. 3, 1st Beichen West Road, Chaoyang District, Beijing 100101, China, qingwei2013@im.ac.cn. It was reported that purified surfactin, mycosubtilin, and plipastatin could be perceived by grapevine plant cells to stimulate grapevine innate immune responses including SA-mediated pathways (Farace et al., 2015). Trends Immunol. Plant Sci. 37, 6971. doi: 10.1007/BF03175560, Li, J., Yan, Q., Zhao, L. H., Zhang, S. M., Wang, Y. X., and Zhao, X. Y. Strain LJ02 colonies show light yellow on LB agar medium. Besides, the long-range elicitation of SA induction in roots may be involved in aforementioned long-range resistance. 26 Articles, This article is part of the Research Topic, Creative Commons Attribution License (CC BY). doi: 10.1007/s11738-003-0019-y, Porcel, R., Zamarreno, A. M., Garcia-Mina, J. M., and Aroca, R. (2014). Error bars indicate standard deviation among triplicates. Plant. 60, 379406. A. (2015). We highly appreciate the constructive suggestions from two professional reviewers. Typically, SAR can perceive the invasion of pathogens by initiate defensive responses via the synthesis of SA and the coordinate activation of a large set of PR proteins and resistance-related enzymes (Feys and Parker, 2000). The data of disease index, CE, resistance enzyme activities, SA production, germination rate, and fungi pathogen counts in rhizospheres were analyzed by one-way ANOVA. 140, 2737. (1996). As is shown in Figure 3A, the treatment group had a significant increase in SOD production as compared to the control treatment. In line with 7th day, the quantity of fungi at 14th day is still significantly less than that of control group (P < 0.01). 6, 11921194. The cake made from sterile MS solid medium without root secretions was used as a control. (1996). The main mechanisms of BCAs include the production of antibiotics, competition, plant growth promotion, and the induction of SAR and ISR (Ramarathnam et al., 2011). Crit. Mol. Control 81, 101110. Overproduction of salicylic acid in plants by bacterial transgenes enhances pathogen resistance. Plant Physiol. Evaluation of biological control agents for managing cucurbit powdery mildew on greenhouse-grown melon. Front. (2011). And another interesting finding of this study is that AG whitefly feeding significantly increased the population density of beneficial BG microflora including actinomycetes and saprophytic fungi that may induce systemic resistance (Yang et al., 2011). 99, 4656. (2010). J. Zhejiang. Both LJ02BC and LJ02FS could induce the production of free SA in upper leaves throughout all experiments. Besides, the examination of rhizosphere secretions in solid MS medium was proved to be an effective method that identifies potential BCAs with resistance-induction and anti-fungal activities. Thus, we come to the conclusion that functional SA production was enhanced in cucumber leaves to stimulate SA-mediated defense response, such as the expression of resistance-related enzymes. Control 80, 6369. Among PR genes, PR-1 expression is a paradigm for the co-regulation of PR genes and correlates well with the induction of SAR (Durrant and Dong, 2004). (2009). HPLC chromatogram of SA standard (A) and sample (B), temporal changes of free SA (C) and conjugated SA (D) in cucumber leaves of control and treatment group. doi: 10.1126/science.1147113, Perez-Garcia, A., Romero, D., Fernandez-Ortuno, D., Lopez-Ruiz, F., De Vicente, A., and Tores, J. Beneficial bacteria and pathogens are initially recognized as harmful invaders in order to limit their spreading (Trda et al., 2015). Ann. (2013). Greenhouse trials showed the CE on cucurbits powdery mildew of 70, 90, and 85% after treated with 1% LJ02FB for 7, 14, and 21 days, respectively (Table 1). Figure 2. Plant. MAMP (microbe-associated molecular pattern) triggered immunity in plants. 49, 693700. Biochem. Therefore, it is likely that using gyrB as a phylogenetic marker is reliable in our study and could provide clues for bacillus determination. doi: 10.1128/Iai.74.1.239-247.2006. Vos, P., Garrity, G., Jones, D., Krieg, N. R., Ludwig, W., Rainey, F. A., et al. Plant Biol. Annu. All those results showed that LJ02FB could elicit the defense responses from plant leaves to rhizosphere, suggesting a long-range systemic resistance is induced under our test conditions. Relative expression of PR-1 gene in cucumber leaves after treated with LJ02FB (Treated) and PDB (Control). Analytical Methods Manual of Soil Microorganisms (In Chinese). (2009). Time course of changes in free SA activity in leaves (A) and in roots (B) of control and treatment group. Biological control of soil-borne pathogens by fluorescent pseudomonads. Yamamoto, S., and Harayama, S. (1995). doi: 10.1111/j.1462-2920.2012.02860.x, Durrant, W. E., and Dong, X. 28, 27312739. All statistical analysis was performed with SPSS version 11.5 statistical software (SPSS, Chicago, IL, USA). It is proved that H2O2 appears to be a key element involved in disease resistance to pathogens (Ahmad et al., 2010). Systemic acquired resistance signal transduction. Biol. 74, 239247. doi: 10.1111/j.1365-3059.2007.01684.x, Song, W., Ma, X., Tan, H., and Zhou, J. doi: 10.1007/s10658-005-5995-x, Yang, J., Yi, H., Kim, H., Lee, B., Lee, S., Ghim, S., et al. In previous studies, only one-way signal transduction was investigated, such as AGBG, AGAG, and BGBG (Yi et al., 2011). Front. B. subtilis is known to produce cyclic lipopeptides such as surfactins, iturins and fengycins (Farace et al., 2015). SA as a key immune signal is involved in the regulation of downstream defense genes (Robert-Seilaniantz et al., 2011). Moreover, we determined that TJ02FB-treated cucumber leaves secreted resistance-related substance into rhizosphere against a range of fungi pathogens, suggesting that LJ02 could elicit a long-range systemic resistance in cucumber against pathogens. (2011). 22, Jinjing Road, Xiqing District, Tianjin 300384, China, wangyh@tjau.edu.cn; Qing Wei, State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, No. It was shown to catalyze the deamination of L-phenylalanine to produce cinnamic acid, a substrate feeding into several biosynthetic routes to various classes of phenylpropanoid-derived secondary plant products, including SA (Mauch-Mani and Slusarenko, 1996). Lebeis, S. L., Paredes, S. H., Lundberg, D. S., Breakfield, N., Gehring, J., Mcdonald, M., et al. doi: 10.1006/bcon.1996.0045, Vlot, A. C., Dempsey, D. A., and Klessig, D. F. (2009). A one-way ANOVA was performed (*P < 0.05; **P < 0.01). Another interesting finding in our study is that the SA signaling pathways induced by beneficial bacterium such as LJ02 is likely to function from leaves (aboveground, AG) to roots (belowground, BG; Figure 7B). Nat. A., et al. Eur. Int. Therefore, the established detection method could further promotes the identification of BCAs against agricultural infections or pathogens. Scanning microscope observation of LJ02 under two resolutions: 25,000 (A) and 5,000 (B). Those results led us to conclude that SAR is indeed induced by LJ02 and MAMP is likely to be responsible for the triggering of SA-dependent defense such as SA synthesis and the subsequent pathogen inhibition (Porcel et al., 2014). Biol. To this end, the activity of systemic resistance-related enzymes was firstly examined. Different letters are significantly difference at P < 0.01 according to Duncan multiple range test. Phytochemistry 70, 15811588. Germination rate of F. oxysporum (A), B. cinerea (B), and Alternaria spp. Figure 8. Altogether, the isolated BCA was referred to as B. amyloliquefaciens LJ02 based on its morphological, phylogenetic, physiological, and biochemical characterizations. doi: 10.1111/j.1365-313X.2007.03369.x, Van der Ent, S., Van Wees, S. C. M., and Pieterse, C. M. J. B. Briefly, 20 L of the LJ02FB was dropped onto the leaves including cotyledon under sterile condition at trefoil stage. Plants commonly use plasma-membrane localized pattern recognition receptors (PRRs) to perceive MAMPs/pathogen-associated molecular patterns (PAMPs; Newman et al., 2013). Xu, Y. J., Takvorian, P., Cali, A., Wang, F., Zhang, H., Orr, G., et al. Previous experiments had the same results after they inoculated the pathogens on various plants (Verberne et al., 2000). Both group induced a rapid increase of PAL activity levels in cucumber leaves within 13 days. Int. Microbiol. Subsequently, we found that when we separated the LJ02FB into LJ02BC and LJ02FS, LJ02BC played very important roles in inducing the production of free SA in both upper uninoculated leaves and in roots. Activities of superoxide dismutase (SOD) isoforms during growth of Scenedesmus (Chlorophyta) species and strains grown in batch-cultures. Based on current data and those previous studies, we summarized our results and some hypotheses in Figure 8. A one-way ANOVA was performed (*P < 0.05; **P < 0.01). Environ. Therefore, LJ02 could employ MAMP to stimulate SA accumulation in both AG (SAR) and BG (SA signaling pathway) and in doing so to exert its biocontrol activities against a wide range of foliar and rhizospheric pathogens. Control 65, 1423. Res. J. Syst. Recently, the bidirectional signal exchanges between AGBG was identified as another type of induced resistance response. Interplay of signaling pathways in plant disease resistance. Duncans multiple-range test was applied when one-way ANOVA revealed significant differences (P < 0.05). As can be seen from our results (Figure 7) that MAMP associated with LJ02 is perhaps the underlying mechanism for the SA accumulation in cucumber tissues since we could detect the increase of SA production when treated with LJ02BC. To further dissect the functions played by bacterium and its fermented substances of LJ02FB, we separated them by centrifugation and kept bacterial cells in 10 mM MgCl2 solution (LJ02BC) and filtered the supernatants to rule out the contamination of bacterial cells to harvest fermented substances (LJ02FS). doi: 10.1038/77347, Verhaar, M. A., Hijwegen, T., and Zadoks, J. C. (1996). Ecotoxicol. (2015). Copyright 2015 Li, Gu, Li, Xu, Wei and Wang. Bacillus amyloliquefaciens GA1 as a source of potent antibiotics and other secondary metabolites for biocontrol of plant pathogens. doi: 10.1016/j.ecoenv.2011.11.008. But the activity of PPO increased rapidly after 2 days and became significant different (P < 0.05) from the control at 3rd day. The powdery mildew fungus Podosphaera fusca (synonym Podosphaera xanthii), a constant threat to cucurbits. doi: 10.4161/psb.6.8.15780, Zhang, Z., Jiang, W., Jian, Q., Song, W., Zheng, Z., Wang, D., et al. Controlling powdery mildew caused by Sphaerotheca fuliginea in cucumber by foliar sprays of phosphate and potassium salts. doi: 10.1016/j.plaphy.2011.03.018, Tamura, K., Peterson, D., Peterson, N., Stecher, G., Nei, M., and Kumar, S. (2011). (2003). Simultaneous expression of choline oxidase, superoxide dismutase and ascorbate peroxidase in potato plant chloroplasts provides synergistically enhanced protection against various abiotic stresses. This is likely to be caused by the degradation of potential elicitors in fermentation broth. To this end, we analyzed the level of transcription of PR-1 gene, a commonly used maker for SA-mediated expression (Tornero et al., 1997). Table 1. Phytopathol. All features are highly identical to those of B. amyloliquefaciens described in Manual of Systematic Bacteriology (Vos et al., 2009). In doing so, we could examine the effects of both fractions (LJ02BC and LJ02FS) on the production of SA in cucumber tissues with spatial and temporal scales. doi: 10.1146/annurev.phyto.42.040803.140421, Esterbauer, H., Schwarzl, E., and Hayn, M. (1977). Changes in pathogenesis-related proteins in pepper plants with regard to biological control of phytophthora blight with Paenibacillus illinoisensis. (2015). doi: 10.1111/j.1364-3703.2008.00527.x, Pokora, W., Reszka, J., and Tukaj, Z. Sci. doi: 10.1016/0003-2697(77)90262-7, Faheem, M., Raza, W., Zhong, W., Nan, Z., Shen, Q. R., and Xu, Y. C. (2015). Time course of changes in SOD activity (A), PPO activity (B), POD activity (C), and PAL activity (D) in cucumber leaves of control and treatment group. A renaissance of elicitors: perception of microbe-associated molecular patterns and danger signals by pattern-recognition receptors. Each treatment was repeated three times and cultured at 28C for 9 days. This phenomenon led us to conclude that LJ02 could induce a long-range of defense response by promoting the free SA production, which will then elicit the SA signaling pathways to enhance the immunity of cucumber plants systemically. Immun. Interestingly, as an major defensive enzyme, SOD showed significantly elevated activity. The search for the BCA against powdery mildew has been a long standing practice for plant pathologists. Plant Microbe Interact. Control 6, 353360. 7H2O: 0.5 g, agar: 15 g, 1% Rose Bangal: 0.33 mL, 1% streptomycin: 3 mL, distilled water: 1,000 mL; Xu and Zheng, 1986) and incubated at 25C. Biocontrol. A one-way ANOVA was performed (*P < 0.05; **P < 0.01). Physiol. A revised medium for rapid growth and bioassays with tobacco tissue cultures. Mol. (2015). Biol. doi: 10.1146/annurev.phyto.050908.135202. doi: 10.1016/j.it.2014.05.004, Keywords: powdery mildew, biocontrol agent, Bacillus amyloliquefaciens, salicylic acid, PR genes, systemic acquired resistance, Citation: Li Y, Gu Y, Li J, Xu M, Wei Q and Wang Y (2015) Biocontrol agent Bacillus amyloliquefaciens LJ02 induces systemic resistance against cucurbits powdery mildew. Most spores would germinate at 9 h in the preliminary period. The LJ02FS is also functional to stimulate the SA production both in upper leaves and roots but not as potent as that of LJ02BC. 77, 486494. 10, 153160. (2009). Saf. Genetic distances were computed by Kimura 2-parameter model. Different letters are significantly difference at P < 0.01 according to Duncan multiple range test. Biol. Microbiol. Furthermore, we have proved that LJ02-induced long-range resistance is an appropriate indicator to examine the biocontrol ability, especially the SAR-inducing activity, of different BCAs using solid rhizosphere medium. Front. Plant Physiol. Mol. Trends Genet. Mol. The new approach will broaden our understanding of protective mechanisms by potential BCAs and can be applied to other beneficial microbes. Plant Pathol. Salicylic Acid, a multifaceted hormone to combat disease. 10, 624634. Plant Physiol. (1995). However, we observed that LJ02BC could consistently induce twofold increase in free SA production, suggesting that microbe-associated molecular pattern (MAMP) may be responsible for SA stimulation (Newman et al., 2013). For more details, please refer to main text. Interestingly, LJ02FS could induce significantly higher amount of free SA at 5th day and declined to control level. The number of CFU was recorded on each plate after 3 days. 15, 583606. Wan, H. J., Zhao, Z. G., Qian, C. T., Sui, Y. H., Malik, A. Li, L., and Steffens, J. C. (2002). Two PR-1 genes from tomato are differentially regulated and reveal a novel mode of expression for a pathogenesis-related gene during the hypersensitive response and development. However, with the accumulation of antagonistic substance, the germination of all pathogens spores began to decrease significantly at 5th day and reached the lowest level at 8 9 days. An 1.2 kb gyrB gene fragment was amplified from the strain LJ02 and sequenced. One-hundred-fifteen isolations were collected to test their antagonistic activity according to their inhibitory activity. Spatial and temporal detection of SA with separated LJ02FB components (LJ02BC and LJ02FS). Plant Physiol. Behav. The images were taken from a ultra-high resolution scanning electron microscope SU8010. 35, 345351. Four pieces of MS solid medium cake were inoculated around the fungi cake at a distance of 2.5 cm (treatment group). Plant pattern-recognition receptors. MEGA5: molecular evolutionary genetics analysis using maximum likelihood, evolutionary distance, and maximum parsimony methods. These authors have contributed equally to this work. Besides, the free SA was also increased in roots and it is possible that some beneficial bacteria could also be recruited to rhizospheres to protect plants from pathogenic invasions. 7, 356363. doi: 10.4141/CJPS06035. This data further confirmed that LJ02 could induce a systemic resistance response against pathogens, perhaps through secreting anti-fungal substances into rhizosphere, possibly through leave-to-root translocation or local synthesis of those substances. Biochem. To be specific, when treated with LJ02FB, cucumber seedlings produced significantly high amount of SOD, POD, PPO, and PAL. Figure 6. Phytopathol. Screening for the identification of potential biological control agents that induce systemic acquired resistance in sugar beet. doi: 10.1016/j.foodchem.2014.07.087, Zipfel, C. (2014). Overexpression of polyphenol oxidase in transgenic tomato plants results in enhanced bacterial disease resistance. (2013). Our work demonstrated that the content of free SA in cucumber leaves was kept at a relatively higher level after spraying the LJ02FB. 56, 976986. Thus, we established a method to detect the concentration of SA in LJ02FB-treated cucumber leaves (Figures 4A,B). Genome analysis of Bacillus amyloliquefaciens FZB42 reveals its potential for biocontrol of plant pathogens. Generally, it was believed that beneficial bacteria can make the plant more tolerant to pathogens by stimulating ISR, which was shown to protect above-ground plant tissues and acts through roots to leaves (Van der Ent et al., 2009). 16, 449455. and Pseudomonas sp. 16, 177187. Phytopathol. (2006). The main function of SOD is eliminating the cellular superoxide radical (O2), and the increase of SOD activity can lead to the accumulation of H2O2. Rev. doi: 10.1111/Mpp.12170, Feys, B. J., and Parker, J. E. (2000). 115, 14051412. (2009). A cry for help from leaf to root. This confirmed our speculation that LJ02 could stimulate the SA-mediated SAR response in cucumbers. Production of salicylic acid precursors is a major function of phenylalanine ammonia-lyase in the resistance of Arabidopsis to Peronospora parasitica. Bacillus amyloliquefaciens sp nov, nom rev. Mol. Different letters are significantly difference at P < 0.01 according to Duncan multiple range test. Plant Pathol. 8, 63. doi: 10.1186/1475-2859-8-63, Bargabus, R. L., Zidack, N. K., Sherwood, J. E., and Jacobsen, B. J. Systemic acquired resistance. Residues and dissipation kinetics of triazole fungicides difenoconazole and propiconazole in wheat and soil in Chinese fields. 10, 264272. The inhibition against pathogen fungi of LJ02-induced secretions was detected as described previously with minor modifications (On et al., 2015). This work was supported in part by National Natural Science Foundation of China (31171892; 31300066) and Extension of Agricultural Science and Technology Project funded by Tianjin Agricultural Commission (201304160). Furthermore, the expression of PR-1 gene was detected by qRT-PCR. And there is compelling evidences that SA acts as a signal molecule in plant disease resistance (Vlot et al., 2009) and the PR gene family act as reliable markers of SA-mediated response or SAR (Hunt and Ryals, 1996).
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