Transcriptome Profile Analysis And Signal Transduction Of Resistance Induced By Burdock Fructooligosaccharide In Tobacco

In nature, plants are continuously infected by a wide range of harmful pathogenic microorganisms. The evolutionary between plants and their attackers provided plants with a highly sophisticated defense system. Plants have developed various defence responses against pathogen attack, including reactive oxygen species burst, the accumulation of salicylic acid (SA) and lignin synthesis. These defense responses could also be induced by a class of molecules named elicitor. Elicitor is a kind of compounds trigger a large array of defense responses in host plant, including biotic elicitor and abiotic elicitor. Among biotic elicitor, the oligosaccharide elicitors derived from fungal and plant cell wall polysaccharides can induce resistance to various pathogens at very low concentrations.Burdock fructooligosaccharide (BFO) is a plant reserve carbohydrate, first isolated from the roots of Arcitum lappa by our group. The amount of BFO in the air-dried root tissue is about17.0%. BFO is not only water-soluble, nontoxic and biocompatible, but also has versatile functional properties, which can agree with the demands of modern environmental protection. In our previous works, BFO could enhance plant resistance to several pathogens. In tobacco, BFO could increase the expression of PRs and SA to enhance resistance against tobacco mosaic virus. It is interesting that a reserve oligosaccharide could improve defense responses in plant. However, the transcriptional programming and early signaling pathway after BFO treatment remain unclear, and the underlying molecular mechanism of BFO in plants is still largely unknown. Therefore, we investigated the expressions of key genes involed in signaling pathways and defense reaction after BFO treatment in tobacco by High-throughput sequencing; we researched that the early signal transduction and the relation of NO and ROS in tobacco after BFO treatment by fluorescent probe and related inhibitors. In addition, we also examined the physiological and biochemical changes associated with resistance in plant after the treatment of BFO. The mainly results are as followed:1. In the present study, we compared differential expression profiling of tobacco after treatment with BFO or distilled water (DW). A number of candidate genes that had altered expression in response to BFO were identified. In all,169genes were identified as up-regulated genes. The expressions of243genes were decreased. We investigated the expressions of genes involved in defense responses and signaling pathways in BFO treated tobacco plants on a genome-wide scale. GO analysis showed that differentially expressed genes were involved in responses to stress, defense responses, biosynthetic processes, responses to hormone, RNA biosynthetic processes and signaling pathways. Eight differentially expressed genes were selected to test the reliability of Solexa sequencing. The fold changes of differential genes in transcription profile and results by qRT-PCR were similar. The results suggested that the mechanism of BFO enhanced plant resistance might be basically about the SA-mediated pathway, and other hormones also play a role in defense response. Moreover, secondary metabolites were related to constitutive activation of the host defense response in BFO treated tobacco.2. We used tobacco plant material, studied the effect of early signal transduction pathway after BFO treatment in tobacco. The results show that:BFO induced extracellular alkalization in tobacco, extracellular Ca2+influx in tobacco epidermal cells, Ca2+is involved in the nitric oxide (NO) generation after BFO treatment, NO and reactive oxygen species (ROS) generation in tobacco guard cells and leaf tissue; Secondly, we demonstrate NO may act as a messenger in regulating ROS. BFO also induced the expression of the genes encoding PAL and ICS to induce the accumulation of SA. Meanwhile, BFO also induced the expression of the genes encoding NPR1to activite SAR and enhance plant resistance to pathogen.3. The physiological and biochemical changes associated with disease resistance after BFO treatment in tobacco were investigated, and the accumulation of secondary metabolite was detected. The results indicated that BFO could significantly decrease MDA content, increase the content of chlorophyll, soluble protein, soluble sugar and soluble phenols. Meanwhile, BFO treatment could increase the content of total phenolic, flavonoids, lignin and other secondary metabolites. In addition, BFO treatment increased the activity of related enzymes (peroxidase, superoxide dismutase, phenol oxidase) and the expression of related enzyme gene in tobacco. But interestingly, BFO treatment was not able to induce the accumulation of callose.4. In this paper, the effects of trans-2-hexenal on the control of postharvest diseases in tomato fruit were investigated. We indicated that the incidence of natural infection and inoculation by Botrytis cinerea in tomato fruit was significantly decreased after treatment with trans-2-hexenal. Trans-2-hexenal increased the mRNA levels of genes encoding ethylene receptors, lipoxygenase, and the phenylalanine ammonia lyase (PAL), but did not induce mRNA accumulation of the pathogenesis-related proteins (PR-la or PR-5). The activities of peroxidases and PAL and the accumulation of phenolic compounds were significantly enhanced after trans-2-hexenal treatment. The findings suggest that the controlling effects of trans-2-hexenal in postharvest tomato fruit might be related to JA/ET-mediated induced systemic resistance.In summary, the mechanism of BFO enhanced plant resistance might be basically about the SA-mediated pathway, and secondary metabolites play an important role in the induced resistance. Treatment with BFO results in the activation of plant responses, such as medium alkalinization, elevation of cytoplasmic Ca2+concentrations, NO and ROS production. Ca2+is involved in the generation of NO after BFO treatment. NO may act as a messenger in regulating ROS, and induces the expression of PAL and ICS genes to promote the accumulation of salicylic acid. In addition, BFO treatment could reduce the content of MDA, and increase the content of chlorophyll and the activities of defense related enzymes (CAT, POD, PAL, PPO). BFO treatment can induce the accumulation of total phenolics, flavonoids and lignin in tobacco to enhance resistance.