CN111118023B

CN111118023B - Artocarpus heterophyllus gene MfbHLH38 and application thereof

Info

Publication number: CN111118023B
Application number: CN202010044682.1A
Authority: CN
Inventors: 黄卓; 邱嘉睿; 蒋才忠; 向香盈; 王嘉彤; 徐文欣; 朱培蕾; 杨丽; 李巧
Original assignee: Sichuan Agricultural University
Current assignee: Sichuan Agricultural University
Priority date: 2020-01-16
Filing date: 2020-01-16
Publication date: 2021-03-30
Anticipated expiration: 2040-01-16
Also published as: CN111118023A

Abstract

The invention discloses an Artocarpus heterophyllus gene MfbHLH38 and application thereof. The nucleotide sequence of the gene is shown as SEQ ID NO. 1; the amino acid sequence of the protein coded by the gene is shown in SEQ ID NO. 2. According to the invention, the drought and salt tolerance of the plant are improved by researching the drought-resistant bHLH transcription factor of Artocarpus heterophyllus, and the drought and salt tolerance of the plant is improved.

Description

Artocarpus heterophyllus gene MfbHLH38 and application thereof

Technical Field

The invention belongs to the technical field of plant genetic engineering, and particularly relates to a millettia speciosa gene MfbHLH38 and application thereof.

Background

Drought is one of the most severe environmental factors in the plant growth process, limiting plant growth and crop productivity, and further causing significant economic losses. To combat environmental stress factors, plants have evolved a number of complex mechanisms. The interaction of multiple mechanisms enhances the biosynthesis of functional and structural protectants (including osmotic pressure and antioxidants) as well as stress-stress proteins. The various functional proteins involved in these processes are mainly regulated by various types of Transcription Factors (TF), such as MYB, bHLH, DREB and WRKY families. These transcription factors play a crucial role in the signaling network of plants against environmental stimuli.

bHLH is one of the largest transcription factor families in plants, divided into 26 subfamilies. The maize regulatory gene (R) is the first cloned transcription factor of the bHLH family, and since many bHLH transcription factors responsive to abiotic stress have been identified in different plants. In arabidopsis, AtbHLH44 and AtbHLH122 responded to drought stress by reducing the expression of the gene encoding PP2 Cs. In grapes, over-expression of VvbHLH1 increased the tolerance of transgenic arabidopsis to salt and drought by increasing the total flavonoid content. In rice, some bHLH transcription factors are also involved in response to abiotic stress. For example, the rice transcription factor OrbHLH2 regulates ABA-independent salt stress signals in Arabidopsis thaliana by up-regulating the expression of the stress-responsive genes DREB1A/CBF3, RD29A, COR15A and KIN 1. Ectopic expression of OrbHLH001 improves tolerance of transgenic plants to freezing and salt stress, and this function is independent of the CBF/DREB1 cold response pathway. Therefore, the bHLH transcription factor plays an important role in a stress-resistant molecular mechanism and improves the drought resistance of plants.

Artocarpus heterophyllus (Myrothamnus flabellifolia Welw.) is a woody resuscitation plant native to south Africa, has extremely strong tolerance to drought stress, and is an important gene resource to be excavated urgently. The Artocarpus heterophyllus has the characteristics of common resuscitation plants, the production of active oxygen and toxic substances in vivo is minimized under the condition that the physiological function of the plants is nearly stopped, and the Artocarpus heterophyllus also has the specific survival capability of the Artocarpus heterophyllus as the only woody resuscitation plant. However, studies on the Artocarpus heterophyllus bHLH transcription factor in abiotic stress are so far scarce, and therefore, it is very important to perform gene cloning and functional verification on the transcription factor. With the research on molecular mechanisms of various plants, the transgenic technology also becomes an important way for improving landscape plants, and the improvement of the stress resistance of the plants through the transgenic way can also play an important guiding role in enhancing the drought tolerance of the landscape plants.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a millettia speciosa gene MfbHLH38 and application thereof, wherein the gene can quickly respond in a drought dehydration period, and the drought resistance and salt tolerance of crops are improved.

In order to achieve the purpose, the technical scheme adopted by the invention for solving the technical problems is as follows:

a mulukhiya gene MfbHLH38, the coding sequence of the gene is shown in SEQ ID NO.1 or the nucleotide sequence shown in SEQ ID NO.1 is substituted, deleted and/or added with one or more nucleotides, and can code the nucleotide sequence of the same functional protein.

Wherein, the sequence table SEQ ID NO.1 is cloned from Artocarpus heterophyllus leaf RNA through PCR, and the length of the core coding region is 720 bp.

The protein coded by the gene has an amino acid sequence shown in SEQ ID NO.2 or the amino acid sequence shown in SEQ ID NO.2 is subjected to substitution, deletion and/or addition of one or more amino acids, and expresses the amino acid sequence of the protein with the same function.

Wherein, SEQ ID NO.2 consists of 239 amino acids, wherein one of the signals is a double-parting nuclear localization signal 'KKLNHNASERDRRKKIN' positioned at 66aa, the structural domain analysis is carried out on the MfbHLH38 amino acid sequence, the HLH domain is positioned at 71aa to 123aa, and MfbHLH38 is provided with an HLH structural domain and belongs to bHLH transcription factors.

A transgenic cell line comprising the above-described mulukhiya MfbHLH38 gene.

Engineering bacteria containing the MfbHLH38 gene of the Artocarpus millettii.

The millettia speciosa MfbHLH38 is applied to the drought and salt resistant process of plants.

The invention has the beneficial effects that:

1. a transgenic Arabidopsis thaliana with higher tolerance to drought is obtained.

2. The mulukhiya gene MfbHLH38 can quickly respond in the early stage of drought dehydration, and provides theoretical basis and application value for improving the drought and salt tolerance of other plants by using the gene.

Drawings

FIG. 1 shows the result of subcellular localization of the Artocarpus heterophyllus gene MfbHLH38 of the present invention;

FIG. 2 shows the positive identification result of MfbHLH38 transgenic Arabidopsis plants;

FIG. 3 shows the growth status of wild type and transgenic Arabidopsis plants after sodium chloride stress treatment; wherein, FIG. 3a is the plant growth state of wild type and transgenic Arabidopsis seedlings after sodium chloride stress treatment; FIG. 3b shows the growth status of wild type and transgenic Arabidopsis adults after sodium chloride stress treatment;

FIG. 4 shows the growth status of wild type and transgenic Arabidopsis plants after drought stress treatment; wherein, FIG. 4a shows the plant growth status of wild type and transgenic Arabidopsis seedlings after drought stress treatment; FIG. 4b shows the growth status of wild type and transgenic Arabidopsis adults after drought stress treatment;

FIG. 5 stomata measurements of wild type and transgenic Arabidopsis plants; wherein, FIG. 5a is a stomata shape detection map of wild type and transgenic Arabidopsis plants; FIG. 5b is a plot of stomatal openness for wild type and transgenic Arabidopsis plants;

FIG. 6 shows chlorophyll content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress;

FIG. 7 shows proline (Pro) content under drought and sodium chloride stress in wild type and transgenic Arabidopsis plants;

FIG. 8 shows the superoxide dismutase (SOD) content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress;

FIG. 9 shows Peroxidase (POD) content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress;

FIG. 10 shows Catalase (CAT) content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress;

FIG. 11 is Malondialdehyde (MDA) content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress;

FIG. 12 is the in vitro leaf natural water loss rate of wild type and transgenic Arabidopsis plants under drought stress;

FIG. 13 is soluble protein content of wild type and transgenic Arabidopsis plants under drought stress;

FIG. 14 shows the results of Diaminobiphenyl (DAB) staining under drought and sodium chloride stress in wild type and transgenic Arabidopsis plants;

FIG. 15 shows the results of nitroblue tetrazolium (NBT) staining of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress;

FIG. 16 shows hydrogen peroxide (H) under drought and sodium chloride stress in wild-type and transgenic Arabidopsis plants₂O₂) Content (c);

Detailed Description

The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.

EXAMPLE 1 cloning of MfbHLH38 Gene of Artocarpus mandshurica

1. Taking Artocarpus heterophyllus leaves, quickly freezing with liquid nitrogen, and storing in a refrigerator at-80 deg.C for extracting total RNA; the Total RNA extraction is carried out by adopting a Plant Total RNA Isolation Kit purchased from Dolando biology company; synthesis of Michelia Argentina cDNA first strand synthesis was performed using Reverse Transcriptase M-MLV (RNaseH-) from Dalibao Biotech, Inc. according to the product instructions.

Taking the first strand of cDNA synthesized by the kit as an amplification template, and taking the designed F: 5'-TCCCCCGGGATGCTAGCTCTATCTCCTTT-3' (SEQ ID NO.3) and R: 5'-GACTAGTTCATACGATGATGGTACGTA-3' (SEQ ID NO.4) as a primer, adding two enzyme cutting sites of SmaI and SpeI when designing the primer for subsequent enzyme cutting and recombination connection, and carrying out cDNA amplification by RT-PCR, wherein the amplification system is shown in Table 1, and the amplification conditions are as follows: pre-denaturation at 95 ℃ for 3min, denaturation at 95 ℃ for 15s, annealing at 56 ℃ for 15s, extension at 72 ℃ for 1min for 35 cycles, and final extension at 72 ℃ for 5 min.

TABLE 1 PCR amplification System

2. After the PCR is finished, performing electrophoretic analysis, recovering an amplified fragment of about 1188bp by adopting a DNA recovery kit of an OMEGA company, connecting the amplified fragment to a Peasy-T1 Simple cloning vector, transforming escherichia coli DH5 alpha competent cells, selecting white colonies, performing colony PCR to identify positive clones, sending the positive clones to Gentianaceae biotechnology Limited to determine the coding sequence of the MfbHLH38 of the Arthropoda gene, wherein the sequence is shown as SEQ ID NO.1, and translating the open reading frame of the obtained gene into an amino acid sequence by using ORF Finder software, wherein the amino acid sequence is shown as SEQ ID NO. 2.

Example 2 subcellular localization of MfbHLH38

Selecting HindIII and BamHI enzyme cutting sites to design a primer according to the conditions of bases and enzyme cutting sites on a subcellular vector pHB-YFP and the instruction of a Clon ExpressII homologous recombination kit; the primers were synthesized by Chengdu Kongke Biopsis.

Adopting synthesized primers with homologous arms and taking Artocarpus heterophyllus cDNA as a template for amplification, wherein the specific sequences of the primers are as follows:

F：5’-ACCAGTCTCTCTCTCAAGCTTATGCTAGCTCTACTATCTCCTTT-3’(SEQ ID NO.5)

R：5’-GCTCACCATACTAGTGGATCCTACGATGATGATGGTACGTA-3’(SEQ ID NO.6)

recovering the PCR product obtained by amplification, connecting the PCR product with a pHB vector cut by HindIII and BamHI endonucleases to construct a fusion vector 35S, wherein MfbHLH38-pHB-YFP, the wild type native tobacco leaf transferred into pHB-YFP plasmid and the wild type native tobacco leaf transferred into 35S are sliced, and the observation result under a laser confocal microscope is shown in figure 1; as can be seen from FIG. 1, the fluorescence signals of only the tobacco leaves transferred with pHB-YFP are distributed at various positions in the tobacco cells, while the fluorescence signals of only the tobacco leaves transferred with MfbHLH38-pHB-YFP plasmid appear only in the cell nucleus, which indicates that the MfbHLH38 gene is localized and plays a role in the cell nucleus.

Example 3: genetic transformation of MfbHLH38 Gene

The agrobacterium LBA4404 competent cells are placed on ice to be unfrozen, 5 mu L of recombinant plasmid 35S is taken, pGSA1403-MfbHLH38 is placed in 100 mu L of competence, the mixture is gently mixed by a gun head, ice bath is carried out for 30min, liquid nitrogen is quickly frozen for 1min, water bath at 37 ℃ is carried out for 5min, the mixture is placed on ice for 2min, 800 mu L of LB liquid culture medium is added, and the mixture is cultured for 2-4 h at 29 ℃ and 120r/min in a constant temperature incubator. Uniformly coating the bacterial liquid in an LB solid culture medium containing 10 mu g/mL chloramphenicol, placing the mixture in a constant-temperature incubator at 28 ℃ for culture, then selecting single bacterial plaque, inoculating the single bacterial plaque in 5mL LB liquid culture medium, and performing shaking culture at 28 ℃ and 250r/min for 24 hours. Transferring 1mL of the above bacterial solution into 50mL of LB liquid culture medium containing 10. mu.g/mL of chloramphenicol, performing shake culture at 28 deg.C and 250r/min to OD₆₀₀1.5 is approximately distributed; centrifuging the bacteria solution with OD value up to standard at 4 deg.C and 8000r/min for 10min, collecting thallus, discarding supernatant, resuspending thallus with 5% sucrose solution of the same volume, adding Silwet-77 into the bacteria solution, and mixing to make the solution concentration reach 0.02% and the OD of the bacteria solution₆₀₀≈0.8。

Before transformation, mature fruit pods are cut off, plants are inverted and immersed into the agrobacterium tumefaciens cell suspension for 2min, then the immersed plants are wiped dry by using filter paper and wrapped by using a plastic film, normal culture is carried out in a light culture box after dark treatment for 24h, and impregnation can be repeated once after one week. And (5) harvesting seeds after the seed pods are yellowed, and marking as T0 generation. Continuing to put the T0 generation Arabidopsis seeds into a culture medium containing 50 ug/mL kanamycin, the plants with the exogenous genes can grow on the kanamycin-containing resistant culture medium, but the non-transgenic plants can not grow normally. Therefore, the plants which can grow normally and have dark green color are selected, DNA is extracted from the dark green plants and PCR detection is carried out to obtain positive T (as shown in figure 2)₂Generation of transgenic plants, wherein，“H₂O' and WT are negative controls, and 1-15 target gene detection bands are positive plants. And repeating the screening step until a positive overexpression pure line plant is screened out.

Example 4: stress treatment of transgenic Arabidopsis

(1) For seedling treatment, wild type and over-expressed T3 generation pure lines (Line A, Line D, Line Q) were sown separately in 1/2MS medium containing NaCl (50mM,100mM, 150mM), mannitol (200mM, 250mM, 300mM) and control group added with only normal components, designated as 1/2 MS. The three strains in each square culture dish are divided into two rows and dibbled, each row is about 15 strains, each treatment is repeated three times, after dark treatment at 4 ℃ for 2d, the strains are moved into an illumination culture box to be vertically placed, the strains are continuously cultured for 2 weeks, and the strains are photographed under a root system analyzer and the root length is measured.

The seedling phenotype under salt stress is shown in figure 3, wherein figure 3a is the plant growth state of wild type and transgenic arabidopsis seedling plants after sodium chloride stress treatment; FIG. 3b shows the growth status of wild type and transgenic Arabidopsis adult plants after sodium chloride stress treatment.

The seedling phenotype under drought stress is shown in FIG. 4, wherein FIG. 4a is the plant growth state of wild type and transgenic Arabidopsis seedling plants after drought stress treatment; FIG. 4b shows the growth status of wild type and transgenic Arabidopsis adult plants after drought stress treatment.

For adult plants, seeds of wild Arabidopsis (WT) and over-expression T3 generation pure lines (Line A, Line D and Line Q) are sown in 1/2MS circular culture dishes, are treated in the dark at 4 ℃ for 3D, then are moved into a light incubator to be cultured until the seeds are four leaves, then are moved into a flowerpot, and are cultured for about 3 weeks, and plants with consistent growth vigor are selected for stress resistance analysis.

(2) Salt stress treatment: the control group was untreated and designated CK, and the remaining groups were treated with 300mM NaCl solution every 3 days. Differences in phenotype between WT and over-expressed plants were observed after 2 weeks (see figure 3); 30 replicates per strain.

(3) Drought stress treatment: a control group is marked as CK, normal watering management is carried out, the rest groups are not watered to ensure that the plants are naturally drought and lose water, photographing is continuously carried out during the period, the growth condition of the plants is recorded, rehydration begins after about 3 weeks of water loss, and photographing observation is carried out during the treatment period (as shown in figure 4); 30 replicates per strain.

Chlorophyll, proline (Pro), superoxide dismutase (SOD), catalase (POD), antioxidase (CAT), Malondialdehyde (MDA), natural water loss rate of isolated leaves, soluble protein, Diaminodiphenyl (DAB), nitroblue tetrazolium (NBT) and hydrogen peroxide (H)₂O₂) The samples were sampled 5 days after the sodium chloride treatment and 7 days after the drought treatment.

Through researching the phenotypes of wild-type and over-expressed arabidopsis seedlings and adult plants under drought and sodium chloride stress, the Line A, Line D and Line Q of over-expressed MfbHLH38 gene strains are obviously stronger than WT in drought and salt tolerance, and the fact that the over-expressed MfbHLH38 gene improves the salt and drought stress resistance of arabidopsis.

(4) Measurement of pore opening under mannitol treatment

Seeds of wild arabidopsis (WT) and over-expression T3 generation pure lines (Line A, Line D and Line Q) are sowed in a 1/2MS circular culture dish, are placed in a light incubator for culture for 7 days after being treated in dark at 4 ℃, are transplanted into 50-hole trays (nutrient soil is equally distributed and sufficient water is poured), and the culture is continued for about 4 weeks.

Leaf of Lotus throne leaves of WT, Line A, Line D and Line Q, 10 pieces of epidermis on the lower surface of each Line were taken and placed in 100mL of MES-KCl buffer (50mM KCl, 0.1mM CaCl)₂10mM MES, pH 6.15) for 2.5h, and then 5 pieces of the hypodermis of each strain were placed in 100mL MES-KCl buffer (50mM KCl, 0.1mM CaCl) containing neither nor 300mM mannitol, respectively₂10mM MES, pH 6.15), under light for 2h, observing under a fluorescence microscope (10 x 40) after treatment, taking the stomata closure degree (width to length ratio) as an index for counting the stomata opening, randomly selecting 4 fields for each epidermis, randomly measuring 5 stomata for each field, and counting 100 stomata cells in total, wherein fig. 5a is the stomata shape and the stomata closure degree of wild type and transgenic arabidopsis plants; FIG. 5b is a histogram of stomatal width to length ratios of wild type and transgenic Arabidopsis plants, and in FIG. 5b each set of test data is a histogramThe graph shows the detection results of WT, Line a, Line D, and Line Q in order from left to right.

As can be seen from the observation of the stomatal phenotype of WT and overexpression lines (see FIG. 5a), the stomatal closure degree (width-to-length ratio) of Line A, Line D and Line Q of overexpression plants is much smaller than that of wild-type plants under the treatment of 300mM mannitol, and the statistical analysis of 100 stomatal data shows that the stomatal closure degree of overexpression plants is significantly smaller than that of WT (see FIG. 5b), which is very significant. Therefore, under the condition of 300mM mannitol simulated drought treatment, the dehydration resistance of the plant over-expressing MfbHLH38 is better than that of a wild plant.

(5) Measurement of chlorophyll content

0.5g of the differently treated fresh leaves were cut into pieces, the veins of the leaves were cut off and the leaves were cut off, added to 50mL brown flasks, 50mL of 95% ethanol were added, respectively, and the flasks were stoppered and placed in a 25 ℃ incubator for extraction in the dark for 48 h. Injecting the chlorophyll extract into an enzyme label plate, placing into an enzyme label instrument for measurement, adding ethanol into another hole as a reference, and measuring the optical density of the pigment solution at 665nm and 649nm wavelengths respectively.

Chlorophyll a content (mg/g): ca ═ V/m (13.7a665-5.76a 649); chlorophyll b content (mg/g): cb ═ V/m (25.8a649-7.6a 665); total chlorophyll content (mg/g): ca + b ═ Ca + Cb; wherein Ca + b is the total content of chlorophyll, Ca is the content of chlorophyll a, Cb is the content of chlorophyll b, V is the volume of the extracting solution, and m is the sample mass. The results are shown in fig. 6, namely the chlorophyll content of wild type and transgenic arabidopsis plants under drought and sodium chloride stress, in each group of detection data in the graph, the bar graphs sequentially show the detection results of WT, Line a, Line D and Line Q from left to right.

Line A, Line D and Line Q of the overexpression MfbHLH38 strain can still maintain higher chlorophyll content under the conditions of drought treatment for seven days and sodium chloride treatment for five days, the chlorophyll content of each transgenic gene is up-regulated after drought stress, and the chlorophyll content of WT is obviously reduced. The result shows that the over-expression MfbHLH38 gene shows better tolerance to drought and salt stress than the wild Arabidopsis.

(6) Determination of proline (Pro) content

Taking 0.5g of each fresh leaf sample of different treated plants, adding a little quartz sand and a little 3% sulfosalicylic acid solution, grinding in a mortar, pouring into a 10mL centrifuge tube, metering to 10mL, and centrifuging at 4500r for 3 min. The supernatant was taken and made up to 10mL with a 3% solution of sulfosalicylic acid. Absorbing 2mL of extracting solution into a clean dry glass test tube, adding 2mL of acidic ninhydrin and 2mL of glacial acetic acid, heating at 100 ℃ for 1h, placing into ice water to terminate the reaction, adding 4mL of toluene, fully oscillating for 15-20 s, standing for layering, then slightly absorbing the upper red solution into a cuvette by using a pipette gun, taking the toluene as a reference, carrying out color comparison at the wavelength of 520nm of a spectrophotometer, and obtaining the absorbance value, and repeating the step twice.

The proline content is (mu g/g) ═ c x v/a)/w, wherein c is the proline solution concentration to be measured which is obtained according to a standard curve, v is the volume of the solution to be measured, a is the volume of the night to be measured, and w is the mass of the sample. The results are shown in fig. 7, namely the proline content of wild type and transgenic arabidopsis plants under drought and sodium chloride stress, in each group of detection data in the graph, the bar graphs sequentially show the detection results of WT, Line a, Line D and Line Q from left to right.

When the strain is stressed by adversity, the proline accumulation amount in the WT body is increased to a certain extent, but the proline synthesis amount in the overexpression MfbHLH38 strains Line A, Line D and Line Q is far higher than that in the wild type. The result shows that the overexpression of the MfbHLH38 gene can enable arabidopsis thaliana to better adapt to severe environment under drought and salt stress conditions.

(7) Determination of superoxide dismutase (SOD) content

Respectively taking Met: 162mL, EDTA-Na 2: 6mL, NBT: 6mL, riboflavin: 6mL of the solution was mixed in a beaker for further use. And (3) absorbing 40 mu L of enzyme solution, respectively adding 3mL of mixed reaction solution, taking two test tubes as a control, adding 40 mu L of phosphate buffer solution and 3mL of mixed reaction solution as a blank control, and wrapping 40 mu L of phosphate buffer solution and 3mL of mixed reaction solution with tinfoil paper in a dark place for zero adjustment during measurement. The tube was placed in a light incubator at 4000Lux and reacted at 25 ℃ for 20 min. The absorbance of each reaction solution at 560nm was measured by zeroing the tube in the dark.

The SOD activity unit takes the inhibition of NBT photochemical reduction by 50% as an enzyme activity unit (U), and SOD total activity (U/g.FW) ═ Ack-AE x V/(Ack x 0.5 x W x Vt), wherein, Ack is the absorbance value of an illumination tube, AE is the absorbance value of a light shielding tube, V is the total volume (mL) of a sample solution, Vt is the dosage (mL) of the sample during measurement, and W is the fresh weight of the sample. The results are shown in FIG. 8, namely the SOD content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress, in each group of detection data in the graph, the bar graphs sequentially show the detection results of WT, Line A, Line D and Line Q from left to right.

Superoxide dismutase can remove superoxide anion free radical in plant body, and improve plant stress resistance. The measurement results show that the SOD activities of leaves of WT, Line A, Line D and Line Q strain plants are increased to different degrees under drought and salt stress, the SOD activities of the Line A, Line D and Line Q strain plants are higher than that of the WT strain plants, the Line A difference of the transgenic strain is obvious, and the Line D and Line Q difference is extremely obvious.

(8) Determination of Peroxidase (POD) content

Preparing POD reaction liquid, putting 50mL of 0.1M phosphate buffer solution with pH 6.0 into a beaker, adding 28 μ L of guaiacol, heating and stirring by a magnetic stirrer to completely dissolve, cooling, adding 219 μ L of 30% H2O, mixing, and storing in a refrigerator. 40 mu L of enzyme solution and 3mL of reaction solution are mixed in a test tube, and 40 mu L of phosphate buffer solution and 3mL of reaction solution are added into a control tube. Readings were taken every 1min at OD-470 nm, three times in total, with 1 peroxidase activity unit (u) as a delta a470 change of 0.01 per minute.

POD activity (U/g.fw.min) ═ Δ a470 × Vt/(W × Vs × 0.01 × t), where Δ a470 is the change in absorbance during the reaction time, Vt is the total volume (mL) of the extract solution, W is the fresh weight (g) of the sample, Vs is the volume (mL) of the enzyme solution taken up at the time of measurement, and t is the reaction time (min). The results are shown in FIG. 9, namely POD content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress, in each group of detection data in the graph, bar graphs sequentially show the detection results of WT, Line A, Line D and Line Q from left to right.

Peroxidase has a very close relation with respiration, photosynthesis, etc. of plants, and it can reflect metabolic changes of plants in a certain period. The measurement results show that the POD activities of leaves of the WT, Line A, Line D and Line Q strain plants are increased to different degrees under drought and salt stress, the POD activities of the Line A, Line D and Line Q strain plants are higher than that of the WT strain, part of the differences are obvious, and part of the differences are extremely obvious.

(9) Catalase (CAT) Activity assay

CAT reaction solution was prepared by adding 0.3092mL of 30% H to 200mL of PBS (0.15M, pH7.0)₂O₂Shaking up (stock solution). 20 mu L of enzyme solution and 3mL of reaction solution are put in a cuvette and read once every 1 minute at 470nm for three times, blank control 20 mu L of distilled water and 3mL of reaction solution are used as control to be adjusted to zero, and the variation value of absorbance per minute (delta A470/mgFW) represents the magnitude of the enzyme activity.

CAT (Δ a470/mgFW) [ Δ a240 × Vt ]/(W × Vs × 0.01 × t), where Δ a 240: is the change in absorbance over the reaction time; w is the sample fresh weight (g); t is reaction time (min); vt is total volume (mL) of the extracted enzyme solution; vs is the volume of enzyme solution taken up (mL) at the time of the assay. The results are shown in FIG. 10, namely the CAT content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress, in each group of detection data in the graph, the bar graphs sequentially show the detection results of WT, Line A, Line D and Line Q from left to right.

The catalase activity can reflect the metabolic strength of the plant and the stress tolerance and disease resistance of the plant. The measurement results show that the CAT activities of the leaves of the WT, Line A, Line D and Line Q strain plants are increased to different degrees under drought and salt stress, the CAT activities of the Line A, Line D and Line Q strain plants are higher than those of the WT strain, part of the differences are obvious, and part of the differences are extremely obvious.

(10) Determination of Malondialdehyde (MDA) content

Weighing 0.5g of stressed leaf, adding quartz sand and 2mL of 10% trichloroacetic acid, grinding to obtain homogenate, adding 8mL of 10% trichloroacetic acid, further grinding, centrifuging the homogenate at 4000r/min for 10min, and collecting the supernatant as malondialdehyde extract. 3 sample tubes (three replicates) were taken, 2mL of each extract was added, 2mL of distilled water was added to the control tube, and 2mL of 0.6% thiobarbituric acid solution was added to each tube. Shaking, reacting the mixture in boiling water bath for 15min, rapidly cooling, and centrifuging. And (3) injecting the supernatant into an enzyme label plate, placing the plate into an enzyme label instrument, and measuring the absorbance (A) values at the wavelengths of 532 nm, 600 nm and 450nm respectively.

MDA concentration (μmol/L) 6.45 × (a532-a600) -0.56 × a 450; the MDA content (μmol/g.f.w) ═ C (μmol/L) × Vt/(Vm (ml) × W (g)), where C is the MDA concentration, Vt is the total volume of the extract, Vm is the total volume of the extract at the time of measurement, and W is the fresh weight of the sample. The results are shown in fig. 12, i.e. MDA content of wild type and transgenic arabidopsis plants under drought and sodium chloride stress.

Under stress conditions, plants typically undergo membrane lipid peroxidation, which in turn produces malondialdehyde. The content of malondialdehyde can reflect the degree of peroxidation of plant cell membrane lipid and the strength of stress resistance. And measuring the malondialdehyde content of the leaves of the plants of each line. The results are shown in FIG. 11, in which the bar graphs sequentially show, from left to right, the detection results of WT, Line A, Line D, and Line Q in each set of detection data

According to the detection results in FIG. 11, under drought and salt stress, the MDA content of the leaves of the WT, Line A, Line D and Line Q Line plants is increased to different degrees, and the MDA content of the Line A, Line D and Line Q Line plants is lower than that of the WT Line plants, so that part of differences are significant, and part of differences are very significant.

(11) Measurement of natural water loss rate of in-vitro blade

Watering the plant cultured in the hole tray to enough moisture, slightly shearing off rosette leaves with scissors to sample, weighing 0.5g leaves of each of the three strains on a balance by using quantitative filter paper, wherein the water content of the leaves is the initial water content and is recorded as m₀Then, the leaves are put into a constant-temperature illumination incubator to be naturally dry (25 ℃,60 percent relative humidity), and the instant weight of the leaves is weighed in 1h, 2h, 3h, 4h, 5h, 6h and 7h respectively.

Real-time water loss rate wr (m) at each time point₀-m_t/m₀) 100% of m, wherein_tFor the instantaneous water content at each time point, m₀Is the initial moisture content. The results are shown in FIG. 12, i.e.wild type and transgenic Arabidopsis plants are in the stemThe natural water loss rate of the leaves in vitro under drought stress.

Under the same condition, each strain has a continuous water loss trend along with the time, and although the water loss rate of the transgenic strains Line A, Line D and Line Q continuously rises, the water loss rate is always lower than WT, and the water loss rate is always in a stable and gentle increasing state, so that the transgenic strains can better control the self functions to adapt to the change of the environment, the damage rate of the plants caused by external adversity stress is slowed down, and some irreversible organism damage can be reduced to the minimum.

(12) Determination of soluble proteins

Weighing 0.5g of fresh sample, grinding the fresh sample into homogenate by using 5mL of phosphate buffer solution, centrifuging the homogenate at 3000r/min for 10min, and reserving the supernatant for later use. This is the experimental plant enzyme solution. Sucking 1.0mL of sample extract (diluted properly according to protein content), placing in a test tube (each sample is repeated for 2 times), adding 5mL of Coomassie brilliant blue reagent, shaking up, standing for 2min, carrying out color comparison at 595nm, measuring absorbance, and searching for protein content by a standard curve.

The content of soluble protein (mg/g) of the sample is C × Vt/(1000 × Vs × W), wherein: c, checking a standard curve value, namely mu g; vt is total volume of extract, mL; w is the fresh weight of the sample, g; vs-sample addition at assay, mL. The results are shown in FIG. 13, namely the soluble protein content of wild type and transgenic Arabidopsis plants under drought and sodium chloride stress, in each group of detection data in the graph, the bar graphs sequentially show the detection results of WT, Line A, Line D and Line Q from left to right.

The soluble protein is one of plant storage substances, is an important nutrient substance and an osmotic adjusting substance in an organism, and the accumulation and the increase of the substance play an important role in the water retention capacity of cells and can also reduce the damage degree of cell membranes to a certain degree. When the strain is stressed by adversity, the accumulation amount of proline in the WT body is increased to a certain extent, but the synthesis amount of soluble protein in the overexpression MfbHLH38 strains Line A, Line D and Line Q is far higher than that of the wild type. The result shows that the overexpression of the MfbHLH38 gene can enable arabidopsis thaliana to better adapt to severe environment under drought and salt stress conditions.

(13) Diaminobenzidine (DAB) and Nitrobluetetrazolium (NBT) staining

The leaves of arabidopsis thaliana after different treatments were cut at room temperature, completely soaked in 10mM phosphate buffer (pH 7.8) containing 1mg/mL DAB (NBT), dark-treated for 8-10h (light-treated for 24-30h) until dark brown (dark blue) spots appeared on the leaves, and then the leaves were decolorized in 95% ethanol, and photographed and recorded after the leaves became transparent. The results are shown in fig. 14 and 15, namely DAB and NBT staining results of wild type and transgenic arabidopsis plants under drought and salt stress.

According to the areas and the depths of dark brown (dark blue) spots appearing on leaves of arabidopsis thaliana, it can be seen that the leaf spots of lines A, Line D and Line Q of strains over-expressing MfbHLH38 genes are less than that of WT, which indicates that the MfbHLH38 transgenic genes can enable arabidopsis thaliana to accumulate less active oxygen under drought and salt stress, and further better resist the stress environment.

(14) Hydrogen peroxide (H)₂O₂) Determination of content

The determination of the hydrogen peroxide content is carried out according to the method of Nanjing kit instruction. The results are shown in FIG. 16, namely the hydrogen peroxide content of wild type and transgenic Arabidopsis plants under drought and salt stress, in each set of detection data in the graph, the bar graphs sequentially show the detection results of WT, Line A, Line D and Line Q from left to right.

Plants accumulate excessive reactive oxygen species under stress, and the excessive reactive oxygen species can cause severe damage to plant proteins. Under drought and salt stress, the active oxygen accumulation amount of MfbHLH38 gene-transferred lines Line A, Line D and Line Q is less than that of wild Arabidopsis thaliana to different degrees, which shows that the overexpression of MfbHLH38 gene in Arabidopsis thaliana can help plants eliminate the active oxygen accumulation, thereby reducing the damage caused by peroxide.

Sequence listing

<110> Sichuan university of agriculture

<120> Artocarpus heterophyllus gene MfbHLH38 and application thereof

<160> 6

<170> SIPOSequenceListing 1.0

<210> 1

<211> 720

<212> DNA

<213> Artocarpus heterophyllus (Myrothamnus flabellifolia Welw)

<400> 1

atgctagctc tatctccttt gttttcaacc ctgggatggc ccttggaaga cccaataagc 60

catgagcaat attattatca taggcaaaca gaaccttacg attcctttct ccataatttt 120

ccttcacccc agacacagaa aaatcttagt gaatccacag tttctggaac gattactggc 180

ggccaaacga tcgttaagaa gcttaaccac aatgcgagcg agcgtgatcg tcgtaagaag 240

atcaacagct tgttttcctc tctccgatca ttacttcctg cttcggatca aacgaagaaa 300

ttaagcattc cagcaacggt ttcgcgtgtg ttgaagtata taccggaact gcaggagcaa 360

gtcaagagat tgacgaaaaa gaaggaagag attttgtcaa aggtttcaag gcaagaaaaa 420

caatttgcac ttgaaaagcc tacatcaagc aacattggaa gctcattatc tactgtttcg 480

gctgatcggt ttggtgatcg agaattagtt attcaaattt ccacattgaa agtcaaggag 540

agtaaactat gtgaggttct attcaactta gaagcggatg gatttcaact actgaattct 600

acttcatttg aatcctttgg agatagggtc ttctacaatt tacatcttca ggaagaagga 660

ataactcgtg gagtggagcc tgaggtgttg actgaaaaac tacgtaccat catcgtatga 720

<210> 2

<211> 239

<212> PRT

<213> Artocarpus heterophyllus (Myrothamnus flabellifolia Welw)

<400> 2

Met Leu Ala Leu Ser Pro Leu Phe Ser Thr Leu Gly Trp Pro Leu Glu

1 5 10 15

Asp Pro Ile Ser His Glu Gln Tyr Tyr Tyr His Arg Gln Thr Glu Pro

20 25 30

Tyr Asp Ser Phe Leu His Asn Phe Pro Ser Pro Gln Thr Gln Lys Asn

35 40 45

Leu Ser Glu Ser Thr Val Ser Gly Thr Ile Thr Gly Gly Gln Thr Ile

50 55 60

Val Lys Lys Leu Asn His Asn Ala Ser Glu Arg Asp Arg Arg Lys Lys

65 70 75 80

Ile Asn Ser Leu Phe Ser Ser Leu Arg Ser Leu Leu Pro Ala Ser Asp

85 90 95

Gln Thr Lys Lys Leu Ser Ile Pro Ala Thr Val Ser Arg Val Leu Lys

100 105 110

Tyr Ile Pro Glu Leu Gln Glu Gln Val Lys Arg Leu Thr Lys Lys Lys

115 120 125

Glu Glu Ile Leu Ser Lys Val Ser Arg Gln Glu Lys Gln Phe Ala Leu

130 135 140

Glu Lys Pro Thr Ser Ser Asn Ile Gly Ser Ser Leu Ser Thr Val Ser

145 150 155 160

Ala Asp Arg Phe Gly Asp Arg Glu Leu Val Ile Gln Ile Ser Thr Leu

165 170 175

Lys Val Lys Glu Ser Lys Leu Cys Glu Val Leu Phe Asn Leu Glu Ala

180 185 190

Asp Gly Phe Gln Leu Leu Asn Ser Thr Ser Phe Glu Ser Phe Gly Asp

195 200 205

Arg Val Phe Tyr Asn Leu His Leu Gln Glu Glu Gly Ile Thr Arg Gly

210 215 220

Val Glu Pro Glu Val Leu Thr Glu Lys Leu Arg Thr Ile Ile Val

225 230 235

<210> 3

<211> 29

<212> DNA

<213> Artificial Sequence (Artificial Sequence)

<400> 3

tcccccggga tgctagctct atctccttt 29

<210> 4

<211> 27

<212> DNA

<213> Artificial Sequence (Artificial Sequence)

<400> 4

gactagttca tacgatgatg gtacgta 27

<210> 5

<211> 44

<212> DNA

<213> Artificial Sequence (Artificial Sequence)

<400> 5

accagtctct ctctcaagct tatgctagct ctactatctc cttt 44

<210> 6

<211> 41

<212> DNA

<213> Artificial Sequence (Artificial Sequence)

<400> 6

gctcaccata ctagtggatc ctacgatgat gatggtacgt a 41

Claims

1. An MfbHLH38 of a mullein gene, wherein the coding sequence of the MfbHLH38 of the gene is shown as SEQ ID NO. 1.

2. Protein encoded by the gene MfbHLH38 of claim 1, wherein the amino acid sequence of said protein is represented by SEQ ID No. 2.

3. An engineered bacterium comprising the mulukhiya gene MfbHLH38 of claim 1.

4. The use of the millettia speciosa gene MfbHLH38 in the drought-resistant salt-tolerant improvement process of plants as claimed in claim 1.