Use of bacterial exoprotein smf1-1 in plant immune regulation

Abstract

The application discloses application of bacterial exoprotein smf1-1 in plant immune regulation and belongs to the technical field of plant genetic engineering. The application first finds that the bacterial protein smf1-1 can be used as an elicitor to trigger plant immunity and induce plant resistance. The bacterial protein is screened from intercellular fluid of rice leaf tissue after infection of bacterial leaf streak, and the bacterial protein can trigger plant immunity by triggering active oxygen burst and callose deposition and other immune responses, thereby improving the disease resistance of rice plants to the bacterial leaf streak. In addition, the gene can be introduced into plants to obtain a rice resistant variety with improved resistance compared with the wild type. The protein gene provided by the application provides a green and effective prevention method for preventing the bacterial leaf streak of rice and provides a new idea for developing a new plant source pesticide.

Description

Technical Field

[0001] This invention relates to the field of plant genetic engineering technology, specifically to the application of the exoprotein smf1-1 of bacterial leaf streak in plant immune regulation. Background Technology

[0002] Rice (Oryza sativa) is one of the most important food crops. Bacterial leaf streak of rice seriously threatens the high and stable yield of rice in my country. The pathogen causing rice leaf streak (Xanthomonas oryzae) is a Gram-negative bacterium that comes into contact with seedlings through rainwater and irrigation water. Therefore, streak symptoms can appear as early as the seedling stage, primarily affecting the leaves. The damage is severe, causing stunted growth, leaf curling and wilting, impaired grain filling, and an increase in empty grains. Since varieties with high resistance and immunity to bacterial leaf streak have not yet been developed, chemical control remains the primary method for managing the disease.

[0003] Plant cell surfaces contain various receptor proteins that can recognize pathogen-associated molecular patterns (PAMPs) or different types of immune elicitors (proteins, nucleotides, flavonoids, etc.). Through signal cascade amplification, these elicit a series of physiological immune responses, including reactive oxygen species bursts, cell wall thickening (callose deposition), stomatal closure, and upregulation of disease resistance genes. Plant immune elicitors are substances that induce or stimulate immune resistance responses in host plants. They can be recognized by plant surface receptors, similar to PAMP molecules, stimulating plant defense responses and thus inducing resistance against the invasion of pathogens such as bacteria and fungi. The discovery of protein elicitors primarily aims to find those that can induce plant immune resistance. Therefore, finding suitable elicitors to stimulate plant defense responses and induce resistance against the invasion of pathogens such as bacteria and fungi is an urgent problem to be solved in rice breeding and disease control. Summary of the Invention

[0004] In view of the above-mentioned prior art, the purpose of this invention is to provide the application of the exoprotein smf1-1 of bacterial leaf streak in plant immune regulation. This invention is the first to discover that the smf1-1 protein encoded by bacterial leaf streak can act as an elicitor to trigger plant immunity and induce plant resistance, thereby achieving the purpose of controlling plant diseases. Furthermore, introducing this gene into plants can yield rice varieties with enhanced resistance compared to wild-type varieties.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the invention provides the use of bacterial streak causal agent exoprotein smf1-1 in any of the following (1)-(4):

[0007] (1) Enhance the burst of reactive oxygen species in plants;

[0008] (2) Increase callose deposition in plants;

[0009] (3) Inducing the expression of plant defense-related genes;

[0010] (4) Improve the disease resistance of plants.

[0011] Furthermore, the bacterial streak causal agent exoprotein smf1-1 is a protein as shown in (A1) or (A2) below:

[0012] (A1) A protein consisting of the amino acid sequence shown in SEQ ID NO.2 of the sequence listing;

[0013] (A2) A fusion protein obtained by attaching a protein tag to the N-terminus and / or C-terminus of the protein defined in (A1).

[0014] In a second aspect, the invention provides the use of the gene encoding the bacterial streak exoprotein smf1-1 in any of the following (1)-(6):

[0015] (1) Enhance the burst of reactive oxygen species in plants;

[0016] (2) Increase callose deposition in plants;

[0017] (3) Inducing the expression of plant defense-related genes;

[0018] (4) Improve the disease resistance of plants;

[0019] (5) Cultivate plant varieties with improved disease resistance;

[0020] (6) Regulate the pathogenicity of bacterial streak pathogens to plants.

[0021] Furthermore, the gene encoding the bacterial streak causal agent exoprotein smf1-1 is a nucleic acid molecule as shown in i) or ii) below:

[0022] i) The nucleotide sequence is the nucleic acid molecule shown in SEQ ID NO.1;

[0023] ii) Nucleic acid molecules other than those in i) that encode the amino acid sequence shown in SEQ ID NO.2.

[0024] In a third aspect, the present invention provides an expression cassette, recombinant expression vector, or recombinant bacteria containing the gene encoding the bacterial stripe spot disease exoprotein smf1-1, for use in any of the following (1)-(5):

[0025] (1) Enhance the burst of reactive oxygen species in plants;

[0026] (2) Increase callose deposition in plants;

[0027] (3) Inducing the expression of plant defense-related genes;

[0028] (4) Improve the disease resistance of plants;

[0029] (5) Cultivate plant varieties with improved disease resistance.

[0030] A fourth aspect of the present invention provides a method for improving plant immune resistance, comprising:

[0031] Steps for heterologous expression of the bacterial leaf streak pathogen exoprotein smf1-1 in plants;

[0032] Alternatively, spray the plant with the exoprotein smf1-1 of bacterial leaf streak causal agent.

[0033] In the above method, the preferred spraying concentration of the bacterial stripe bacterium exoprotein smf1-1 is 0.01-0.5 mg / ml.

[0034] A fifth aspect of the present invention provides a method for cultivating plant varieties with enhanced disease resistance, comprising the following steps:

[0035] The gene encoding the exoprotein smf1-1 of bacterial leaf streak was transferred into wild-type plants to obtain transgenic plants; the transgenic plants showed higher resistance to bacterial leaf streak than the wild-type plants.

[0036] The gene encoding the bacterial streak causal agent exoprotein smf1-1 is a nucleic acid molecule as shown in i) or ii) below:

[0037] i) The nucleotide sequence is the nucleic acid molecule shown in SEQ ID NO.1;

[0038] ii) Nucleic acid molecules other than those in i) that encode the amino acid sequence shown in SEQ ID NO.2.

[0039] Furthermore, the wild-type plant is rice.

[0040] In a sixth aspect, the present invention provides the application of a plant-derived immune inducer in the control of fungal and / or bacterial diseases of crops; wherein the plant-derived immune inducer uses the exoprotein smf1-1 of the above-mentioned bacterial leaf streak as its active ingredient.

[0041] The beneficial effects of this invention are:

[0042] This invention is the first to discover that spraying rice leaves with exogenously expressed bacterial leaf streak protein smf1-1 significantly reduces the length of bacterial leaf streak lesions on infected rice leaves. Spraying rice leaves with exogenously expressed bacterial leaf streak protein smf1-1 significantly enhances the immune response in rice, increasing reactive oxygen species activity, callose deposition, and MAPK3 / MAPK6 protein phosphorylation levels. Rice plants heterologously expressing bacterial leaf streak protein smf1-1 show greater disease resistance than wild-type plants. Therefore, bacterial leaf streak protein smf1-1 has promising potential for the green control of bacterial diseases. Attached Figure Description

[0043] Figure 1 The image shows the results of Western blot validation. The left side shows the in vitro expression of smf1-1 protein using the recombinant vector, and the right side shows the purified protein.

[0044] Figure 2 The image shows the leaf inoculation status after spraying with exoprotein smf1-1. The left side shows the inoculation photos, and the right side shows the statistical results of lesion length.

[0045] Figure 3 The results of DAB and NBT staining of leaves sprayed with exoprotein smf1-1.

[0046] Figure 4 Fluorescence microscopy observation results of callose deposition in leaves sprayed with exoprotein smf1-1.

[0047] Figure 5 Results of MAPK phosphorylation levels in rice leaf tissues after spraying with the exoprotein smf1-1.

[0048] Figure 6 The expression results of rice defense-related genes OsPAL, OsPR2, and MAPK6 in rice after spraying with the exoprotein smf1-1.

[0049] Figure 7 The results of smf1-1 protein expression and lesion length in wild-type plants and T1 generation resistant plants were statistically analyzed. Detailed Implementation

[0050] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0051] As mentioned earlier, elicitors, as a special class of compounds, can activate plant defense responses. Protein elicitors are one such type, and they have good effects on disease resistance, yield increase, and quality improvement. They induce the expression of plant disease resistance-related genes through the signal transduction system, thereby promoting the production of defense substances, improving plant immunity, and reducing the occurrence of diseases.

[0052] In view of this, the present invention has found that the exoprotein smf1-1 of bacterial leaf streak can act as an elicitor to trigger plant immunity and induce plant resistance. Heterologous expression of the exoprotein smf1-1 gene of bacterial leaf streak in rice can enhance the resistance of rice to bacterial leaf streak.

[0053] The sequence of the smf1-1 gene, an exoprotein of *Scleroderma streakscens*, is shown in SEQ ID NO.1, and is as follows:

[0054]

[0055] The amino acid sequence of the exoprotein smf1-1 of bacterial spot disease bacteria is shown in SEQ ID NO.2, and is as follows:

[0056]

[0057]

[0058] To investigate the function of the exoprotein smf1-1 from *Bacillus streakus*, this invention obtained the exoprotein smf1-1 (smf1-1) through prokaryotic expression and purification. Treatment of rice Zhonghua 11 with the prepared exoprotein smf1-1 (smf1-1) revealed that the exoprotein smf1-1 (smf1-1) promoted an immune response in rice, including reactive oxygen species bursts, callose deposition, and MAPK3 / MAPK6 protein phosphorylation levels. Furthermore, heterologous expression of the exoprotein smf1-1 gene in rice enhanced rice resistance to bacterial leaf streak.

[0059] Based on the above experimental results, it can be determined that the exoprotein smf1-1 of bacterial leaf spot disease and its encoding gene have the effects of promoting growth and preventing disease, thus proposing this invention.

[0060] Based on the above-discovered bacterial stripe causal agent smf1-1 gene, the scope of protection of this invention also includes DNA fragments homologous to the bacterial stripe causal agent smf1-1 gene.

[0061] These DNA fragments homologous to the smf1-1 gene of bacterial streak causal agent include alleles, homologous genes, mutant genes, and derived genes corresponding to the nucleotide sequence of this invention (SEQ ID NO.1), and all fall under the protection of this invention.

[0062] Those skilled in the art can readily mutate the nucleotide sequence of the *S. mf1-1* gene, a bacterial exoprotein of *S. mf1-1*, using known methods such as directed evolution and point mutation. Artificially modified nucleotides having 70% or higher identity with the nucleotide sequence of the *S. mf1-1* gene are derived from and equivalent to the sequences of the present invention, provided their function is equivalent to the nucleotide sequence shown in SEQ ID NO. 1.

[0063] As used herein, the term "identity" refers to sequence similarity to a natural nucleic acid sequence. "Identity" includes nucleotide sequences having 75% or higher, 85% or higher, 90% or higher, or 95% or higher identity with the nucleotide sequence shown in SEQ ID NO. 1 of this invention. The equivalence of amino acid or nucleotide sequences can be determined using the BLAST algorithm (Altschul et al. 1990. Journal of Molecular Biology 215:403-410; Karlin and Altschul. 1993. Proceedings of the National Academy of Sciences 90:5873-5877).

[0064] The aforementioned 70% or more identity can be 70%, 75%, 80%, 85%, 90%, or 95% or more identity.

[0065] This invention selects rice as the target of transgenic research. However, the bacterial leaf streak bacterium exoprotein smf1-1 gene and the plant expression vector containing this gene can also be used to produce other transgenic plants with enhanced disease resistance.

[0066] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0067] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels. Experimental methods without specified detailed conditions are performed according to conventional test methods or the supplier's recommended operating instructions.

[0068] The rice bacterial leaf streak pathogen used in this embodiment of the invention is strain RS105, which is described in the literature "Establishment of the genetic manipulation system of Xanthomonas rice and functional study of hrP gene and avrBs / thA family genes" (Doctoral dissertation of Shanghai Jiaotong University, 2004). The public can obtain it from the applicant to repeat this experiment.

[0069] The experimental crop in this invention is rice (rice variety ZH11). The planting method is as follows: the rice is grown in a greenhouse, with alternating 16 hours of light and 8 hours of darkness each day, at a constant temperature of 28℃ and an air humidity of 60-70%; the greenhouse is located in the National Key Laboratory of Wheat Breeding at Shandong Agricultural University.

[0070] Example 1: Preparation of exoprotein SMF1-1 from bacterial streak causal agent

[0071] Based on the coding sequence of the bacterial streak causal agent exoprotein smf1-1 (as shown in SEQ ID NO.1), the corresponding primers P1 and P2 were designed using Primer5 software, as follows:

[0072] P1(F): 5'-CAAATGGGTCGCGGATCCGAATTCatgaaacagcgtcgccgc-3' (SEQ ID NO. 3);

[0073] P2(R): 5'-AAGCTTTGTCGACGGAGCTCGAATTCttatttcccttccgctacgcaac-3' (SEQ ID NO. 4).

[0074] The genome of bacterial streak causal agent RS105 was extracted using a bacterial DNA extraction kit. Using the genome as a template, PCR amplification was performed using primers P1(F) and P2(R). The PCR program was as follows: 95℃ pre-denaturation for 5 min, 95℃ denaturation for 30 sec, 60℃ annealing for 30 sec, 72℃ extension for 30 sec, for 32 cycles. After a final extension at 72℃ for 7 min, the DNA was ligated into the pET-28a vector using homologous recombination. Sequencing confirmed that the reading frame of the coding region in the expression vector was correct, and the recombinant plasmid was obtained.

[0075] After transfecting the correctly sequenced recombinant plasmid into E. coli competent cells BL21, 4 ml of LB broth containing glucose and kana antibiotic (5 g / L glucose, 100 mg / L kana antibiotic) was transferred and cultured at 37°C for 12 h. The culture was then transferred to 250 ml of LB broth containing kana (50 μg / ml kana antibiotic) and cultured at 37°C until OD (Organic Degrees Per Minute) was reached. 600=Approximately 0.8, and add IPTG (working concentration 1mM) in a clean bench for induction, incubate at 28℃ for 4h, centrifuge (4℃, 6000rpm, 15min), discard the supernatant, wash the cells with 40ml buffer A (50mM Tris-HCl (pH=8.0) + 2mM EDTA + 100mM NaCl), centrifuge again (4℃, 6000rpm, 10min), wash the cells again with an equal volume of buffer A, centrifuge again (4℃, 6000rpm, 10min), discard the supernatant, and use 20ml buffer B (50mM Tris-HCl (pH=8.0) + 1mM EDTA + 100mM NaCl + 1%). The bacterial cells were resuspended in NP-40 solution, then sonicated for 15 min, followed by centrifugation (4℃, 6000 rpm, 15 min). After centrifugation, the protein in the supernatant was denatured, and then Coomassie brilliant blue staining and Western blot verification were performed. The supernatant was then purified by heating at 90℃ for 20 min and centrifuged at 6000 rpm for 10 min to obtain a supernatant containing the bacterial streak causal agent exoprotein SMF1-1.

[0076] The results of Example 1 are as follows Figure 1 As shown, the bacterial streak bacterium exoprotein smf1-1 was expressed and purified, and the protein size was 64 kDa.

[0077] Example 2: Study on the effect of exoprotein smf1-1 of bacterial leaf streak on rice resistance to bacterial leaf streak

[0078] The solution of bacterial leaf streak exoprotein smf1-1 prepared in Example 1 (the concentration of smf1-1 in the spray solution was 10 μg / ml, and the spray volume was 10 ml) was evenly sprayed onto four-week-old ZH11 leaves. Two hours after spraying, two inoculation wells were injected with OD solution diluted with 10 mM MgCl2. 600 =0.5 RS105 strain), statistical observation after 15 days.

[0079] The results are as follows Figure 2 As shown, exogenous application of the bacterial leaf streak pathogen's secreted protein smf1-1 significantly reduced the lesion length of bacterial leaf streak in rice leaves. The experimental results indicate that the bacterial leaf streak pathogen's secreted protein smf1-1 can significantly improve rice's resistance to bacterial leaf streak.

[0080] Example 3: Study on the effect of exoprotein smf1-1 of bacterial leaf streak on inducing reactive oxygen species burst in rice

[0081] A solution of the bacterial leaf streak exoprotein smf1-1 prepared in Example 1 (the concentration of smf1-1 in the spray solution was 10 μg / ml, and the spray volume was 10 ml) was evenly sprayed onto four-week-old ZH11 leaves. Two hours after spraying, the leaves were cut and immersed in a 0.5 mg / mL DAB solution and a 1 mg / mL NaN3 solution under vacuum for 30 minutes. The leaves immersed in the DAB solution were then cultured under light for 8 hours. The leaves immersed in the DAB solution were then transferred to a 1 mg / mL NBT solution and vacuumed for 30 minutes. Afterward, the DAB and NBT solutions used for immersion were replaced with 95% ethanol, and the leaves were destained at 95°C. The DAB and NBT staining was observed using a stereomicroscope.

[0082] The results are as follows Figure 3 As shown, smf1-1-His represents the staining results of the exoprotein smf1-1 from the bacterial leaf streak pathogen. Compared with the control group, the experimental group showed deeper DAB and NBT staining. The experimental results indicate that the exoprotein smf1-1 from the bacterial leaf streak pathogen can significantly stimulate the burst of reactive oxygen species in rice.

[0083] Example 4: Study on the effect of exoprotein smf1-1 of bacterial leaf streak on inducing callose deposition in rice

[0084] The solution of bacterial leaf streak exoprotein smf1-1 prepared in Example 1 (the concentration of smf1-1 in the spray solution was 10 μg / ml, and the spray volume was 10 ml) was evenly sprayed onto four-week-old ZH11 leaves. Two hours after spraying, the leaves were cut off and immersed in a lactophenol mixture [20 ml of phenol (pre-melted in a 60°C water bath) + 20 ml of lactic acid + 8 ml of pure glycerol, then diluted to 100 ml with ddH2O]. The leaves were placed in a vacuum pump with the cap open and evacuated for 30 minutes. Then, they were heated in a 60°C water bath for 30 minutes to decolorize, with the above lactophenol mixture being replaced every 10 minutes. After decolorization, the leaves were washed three times with ddH2O, aniline blue solution was added, and the leaves were left to stand overnight in the dark. Finally, the leaves were washed three times with water, and the callose deposition was observed using a fluorescence microscope.

[0085] The results are as follows Figure 4 As shown, smf1-1-His represents the fluorescence microscopy observation results of the exoprotein smf1-1 of bacterial leaf streak causal agent. The experimental results indicate that the exoprotein smf1-1 of bacterial leaf streak causal agent can significantly induce callose deposition in rice.

[0086] Example 5: Study on the effect of exoprotein smf1-1 of bacterial leaf streak on phosphorylation level of MAPK3 / MAPK6 in rice

[0087] The solution of bacterial leaf streak exoprotein smf1-1 prepared in Example 1 (the concentration of smf1-1 in the spray solution was 10 μg / ml, and the spray volume was 10 ml) was evenly sprayed onto the leaves of four-week-old rice ZH11. Samples were taken at 0 min, 30 min, and 60 min, respectively. Total plant protein was extracted from the samples using protein extraction solution (Century Kangwei Company), and the phosphorylation level of MAPK was detected using p38MAPK antibody.

[0088] The results are as follows Figure 5 As shown, compared with the control group, the MAPK phosphorylation level in the experimental group was significantly higher at 30 min and 60 min after SMF1-1 treatment than at 0 min. This indicates that SMF1-1 can activate the MAPK signaling pathway to mediate downstream defense responses, meaning that SMF1-1 can act as an elicitor to induce plant immunity and enhance the control effect against rice bacterial leaf streak.

[0089] Example 6: The exoprotein smf1-1 of bacterial streak affects the expression of defense-related genes.

[0090] I. Extraction of Total RNA

[0091] The rice variety ZH11 was selected. When the rice seedlings reached four weeks of age, the experimental group was sprayed with a solution of the bacterial leaf streak exoprotein smf1-1 prepared in Example 1 at a concentration of 10 μg / ml and a spray volume of 10 ml. The control group (CK) was sprayed with a solution containing a His-tagged empty vector at a concentration of 10 μg / ml and a spray volume of 10 ml. Two hours later, leaf samples were taken and immediately frozen in liquid nitrogen and stored at -80℃. Equal portions of the leaves were taken, crushed in a mortar, and transferred into 1.5 mL centrifuge tubes containing Trizol lysis buffer. After thorough shaking, total RNA was extracted, and the mass of total RNA was identified by electrophoresis.

[0092] II. Analysis of Disease Resistance Gene Expression

[0093] Design the corresponding real-time quantitative PCR primers P3, P4, P5, P6, P7, and P8 using the website (https: / / www.ncbi.nlm.nih.gov / tools / primer-blast / ), as follows:

[0094] P3(F): 5'-TGCCATTGCCATACACCCAT-3' (SEQ ID NO.5);

[0095] P4(R): 5'-AGCTGAGCAGAGCAGCTAAC-3' (SEQ ID NO. 6);

[0096] P5(F): 5'-CCCCGTCAATTGTGAAACGC-3' (SEQ ID NO.7);

[0097] P6(R): 5'-TCTGGTGACCACTAGCAAGC-3' (SEQ ID NO.8);

[0098] P7(F): 5'-TTCACCGAGACTTGAAGCCC-3' (SEQ ID NO.9);

[0099] P8(R): 5'-GCGTTCCGATGAGCTCCATTA-3' (SEQ ID NO. 10).

[0100] In real-time quantitative RT-PCR, the designed primers P3 and P4, P5 and P6, and P7 and P8 were used to analyze the expression of rice-related disease resistance genes OsPAL, OsPR2, and MAPK6 after inoculation.

[0101] The results are as follows Figure 6 As shown, the expression levels of rice-related disease resistance genes OsPAL, OsPR2, and MAPK6 were all higher than those in the control group. The experimental results indicate that the exoprotein smf1-1 of bacterial leaf streak promotes the upregulation of disease resistance-related genes.

[0102] Example 7: Heterologous expression of the bacterial leaf streak pathogen's secreted protein smf1-1 in rice enhances rice's resistance to the bacterial leaf streak pathogen.

[0103] Genetic transformation of transgenic rice using the 35S promoter to produce the exoprotein smf1-1 from bacterial leaf streak pathogen was carried out as follows:

[0104] The gene encoding the exoprotein smf1-1 of bacterial leaf streak (SEQ ID NO.1) was ligated into the pXUN-HA vector (described in the following literature: Chen, S.; Songkumarn, P.; Liu, J.; Wang, G.-L., A Versatile Zero Background T-Vector System for Gene Cloning and Functional Genomics. Plant Physiology 2009, 150(3), 1111-1121.). The correctly sequenced clone was then transformed into Agrobacterium EHA105. Transgenic transformation of rice was carried out by Wuhan Boyuan Biotechnology Co., Ltd., and T1 generation lines were obtained.

[0105] The genome of T1 generation plants was extracted, and the hygromycin resistance gene was amplified using the genome as a template. Transgenic plants successfully inoculated with the hygromycin resistance gene were screened from the obtained T1 generation lines. Two correctly transformed rice lines were selected and injected into two inoculation wells with OD2 diluted in 10 mM MgCl2. 600 =0.5 RS105 strain), and the lesion length was counted after 14 days. The experiment was repeated 3 times.

[0106] The results are as follows Figure 7 As shown, compared with wild-type plants, the T1 generation resistant plants labeled 4# and 6# expressed SMF1-1 protein and had shorter leaf spots. The experimental results indicate that the transgenic lines of bacterial leaf streak strain smf1-1 exoprotein have significant resistance to RS105.

[0107] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. Application of the exoprotein smf1-1 of bacterial streaks in any of the following (1)-(4): (1) Enhance the reactive oxygen species burst in rice; (2) Improve callose deposition in rice; (3) Inducing the expression of rice defense-related genes OsPAL, OsPR2 and MAPK6; (4) Improve the resistance of rice to bacterial leaf streak; The bacterial streak causal agent exoprotein smf1-1 is a protein as shown in (A1) or (A2) below: (A1) A protein consisting of the amino acid sequence shown in SEQ ID NO.2 of the sequence listing; (A2) A fusion protein obtained by attaching a protein tag to the N-terminus and / or C-terminus of the protein defined in (A1).

2. The application of the gene encoding the exoprotein smf1-1 of bacterial streaky causal agent in any of the following (1)-(5): (1) Enhance the reactive oxygen species burst in rice; (2) Improve callose deposition in rice; (3) Inducing the expression of rice defense-related genes OsPAL, OsPR2 and MAPK6; (4) Improve the resistance of rice to bacterial leaf streak; (5) Develop rice varieties with improved resistance to bacterial leaf streak; The gene encoding the bacterial streak causal agent exoprotein smf1-1 is a nucleic acid molecule as shown in i) or ii) below: i) The nucleotide sequence is the nucleic acid molecule shown in SEQ ID NO.1; ii) Nucleic acid molecules other than those in i) that encode the amino acid sequence shown in SEQ ID NO.

2.

3. The application of expression cassettes, recombinant expression vectors, or recombinant bacteria containing the gene encoding the exoprotein smf1-1 of bacterial streaks in any of the following (1)-(5): (1) Enhance the reactive oxygen species burst in rice; (2) Improve callose deposition in rice; (3) Inducing the expression of rice defense-related genes OsPAL, OsPR2 and MAPK6; (4) Improve the resistance of rice to bacterial leaf streak; (5) Develop rice varieties with improved resistance to bacterial leaf streak; The gene encoding the bacterial streak causal agent exoprotein smf1-1 is a nucleic acid molecule as shown in i) or ii) below: i) The nucleotide sequence is the nucleic acid molecule shown in SEQ ID NO.1; ii) Nucleic acid molecules other than those in i) that encode the amino acid sequence shown in SEQ ID NO.

2.

4. A method for improving the resistance of rice to bacterial leaf streak, characterized in that, include: Steps for heterologous expression of the bacterial leaf streak pathogen exoprotein smf1-1 in rice; Alternatively, the procedure of spraying rice with the exoprotein smf1-1 of bacterial leaf streak pathogen; The bacterial streak causal agent exoprotein smf1-1 is a protein as shown in (A1) or (A2) below: (A1) A protein consisting of the amino acid sequence shown in SEQ ID NO.2 of the sequence listing; (A2) A fusion protein obtained by attaching a protein tag to the N-terminus and / or C-terminus of the protein defined in (A1).

5. The method according to claim 4, characterized in that, The spraying concentration of the exoprotein smf1-1 of bacterial leaf streak is 0.01-0.5 mg / ml.

6. A method for cultivating plant varieties with enhanced disease resistance, characterized in that, Includes the following steps: The gene encoding the exoprotein smf1-1 of bacterial leaf streak was transferred into wild-type plants to obtain transgenic plants; the transgenic plants showed higher resistance to bacterial leaf streak than the wild-type plants. The gene encoding the bacterial streak causal agent exoprotein smf1-1 is a nucleic acid molecule as shown in i) or ii) below: i) The nucleotide sequence is the nucleic acid molecule shown in SEQ ID NO.1; ii) Nucleic acid molecules other than those in i) encoding the amino acid sequence shown in SEQ ID NO. 2; The wild-type plant is rice.

7. The application of plant-derived immune inducers in the control of bacterial leaf streak in rice, characterized in that, The plant-derived immune inducer uses smf1-1, an exoprotein of bacterial leaf streak, as its active ingredient. The bacterial streak causal agent exoprotein smf1-1 is a protein as shown in (A1) or (A2) below: (A1) A protein consisting of the amino acid sequence shown in SEQ ID NO.2 of the sequence listing; (A2) A fusion protein obtained by attaching a protein tag to the N-terminus and / or C-terminus of the protein defined in (A1).

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