Deoxynivalenol (DON) is a secondary metabolite mainly produced by Fusarium
species, such as F. Graminearum
and F. culmorum
. DON is commonly found in food and feed. A three-year survey conducted by Rodrigues and Naehrer (2012) indicated that 79% of corn and 76% of wheat samples were contaminated with DON in North America [1
]. In the southern region of Brazil, 243–2281 μg of DON/kg whole wheat samples was detected in 2012 [2
]. A recent study revealed that DON was the major toxin found in wheat bran, corn, and soybean meal, in Chinese markets [3
]. Gratz and Garcia reported that the level of DON contamination in food is greatly affected by weather and farming conditions [4
DON is also known as vomitoxin because of its effects on livestock; it exerts toxic effects in humans and domestic animals. It can induce apoptosis of various cells, and is well-known for its neurotoxicity, genotoxicity, immunotoxicity, mutagenesis and misshapen effects [6
]. Toxicity studies revealed that DON inhibits eukaryotic protein synthesis, which disrupts cytokine regulation and alters cell proliferation, leading to cell death [7
]. DON was also shown to combine with protein sulfhydryl groups and inhibits mitochondrial protein synthesis, leading to the induction of oxidative stress [8
In recent years, several trichothecene biosynthetic genes (TRI
) revealed in DON biosynthesis were revealed [9
]. Until now, 15 highly conserved genes were found to be closely associated with biosynthesis of Fusarium
trichothecene toxins [10
]. These genes are scattered over different chromosomes, namely TRI5
double cluster and TRI101
]. The TRI5
core cluster consists of 12 genes (TRI3
), which are closely related to TRI5
and are arranged in a DNA fragment of about 30 kb. The TRI5
core cluster encodes several proteins, such as trichodiene synthase (TRI5
], P450 monooxygenase (TRI4
], trichothecenes C-3 esterase (TRI8
], 15-O-acetyltransferase (TRI3
], transcription factors (TRI6
], toxin delivery pump (TRI12
], 4-O-acetyltransferase (TRI7
) and two unknown functional proteins (TRI9
). Terpene cyclase gene TRI5
isolated from F. sporotrichioides
has been reported to be involved in DON synthesis [17
encodes cytochrome P450 monooxygenase in F. sporotrichioides
and F. graminearum
encodes acyltransferase and catalyses the formation of ester side groups at C-8 during trichothecene biosynthesis in F. sporotrichioides
]. The TRI101
encodes 3-O-acetyltransferase, which is able to convert the toxin into a less toxic product [22
The production of DON is regulated not only by TRI
, but also by protein kinases [23
]. There are about 120 predicted protein kinase genes in F. graminearum
. Ochiai reported that the expression level of TRI4
in the F. graminearum
(encoding mitogen-activated protein kinase kinase kinase; MAPKKK), FgOs5
(encoding mitogen-activated protein kinase kinase; MAPKK), and FgOs2
(encoding mitogen-activated protein kinase; MAPK) were markedly reduced in rice medium [24
]. In addition, the toxigenic capability of these mutants was blocked [24
]. Target of rapamycin (TOR) is also a serine/threonine kinase, which plays an important role in cell growth, proliferation, metabolism, protein translation and signaling pathways [25
]. Yu et al. found that FgPPG1
(FGSG_05281) mutants showed a decrease of sporulation and failure to produce DON; FgPPG1
is one of the key TOR genes in F. graminearum
]. In addition, FgPPG1 interacts with FgTip41 (FGSG_06963) to regulate mycelia growth and virulence. It also regulates DON synthesis and F. graminearum
pathogenicity by regulating downstream transcription factor FgAreA (FGSG_08634) [26
is a transcription factor that plays a negative regulatory effect on DON synthesis [28
The molecular mechanism underlying DON biosynthesis in F. graminearum has almost been revealed. However, in the current study, DON-producing capacities of Fg1 and Fg2 strains were stuided. Thus, (i) Expression level of the genes involved in DON synthesis was analyzed by proteomics and transcriptomics analyses of a DON-producing strain, Fg1, and DON non-producing strain, Fg2 and (ii) the possible molecular mechanism underlying DON production by Fg1 was investigated.
In this study, we used two strains—Fg1, DON-producing strain and Fg2, DON non-producing—to analyze the molecular mechanism of DON biosynthesis. The results on the proteomics analysis of the strains revealed 152 differentially expressed proteins, among which, 48 were identified. The GO and functional classification analyses showed that most of the proteins were involved in oxidation-reduction and cell-based metabolism processes. Similarly, the GO analysis performed using the transcriptome data demonstrated that most of the DEGs were classified under oxidation-reduction process, and a positive correlation was observed between the findings of the proteomics and transcriptomics analyses. The results of the transcriptomics analysis revealed that the gene expression profile was different in Fg1 and Fg2. These results demonstrated the difference in phenotypes considering DON production. Hestbjerg et al., (2002) showed a significant correlation between DON concentration and disease index [29
]. However, a majority of the down-regulated genes were involved in localization, establishment of localization and single-organism localization in Fg1. Maier et al. (2006) also reported that DON is pathogenicity factor, which may influence the virulence of F. graminearum
in a complex manner [30
].The results indicated that the pathogenicity of Fg1 may be weaker than that of Fg2, leading to the production of higher amount of toxin influencing the virulence of Fg1.
DON is a derivative of sesquiterpene compounds, which are synthesized by FPP, which is synthesized through MVA and methylerythritol 4-phosphate (MEP)-independent pathways. Pyruvate and glyceraldehyde-3-phosphate are the main substrates of the MEP pathway. Glyceraldehyde-3-phosphate dehydrogenase (protein spots 2, 4 and 8) and 2,3-bisphosphoglycerate mutase (protein spot 59) are the key enzymes required for the production of pyruvate and glyceraldehyde-3-phosphate [31
]. The expression level of these enzymes was significantly higher in Fg1 than in Fg2. The expression level of these two genes followed the same trend. The biosynthesis of FPP can also be achieved through the MVA pathway, which uses acetyl CoA as the only substrate [32
]. Pyruvate dehydrogenase (PDH, spot 18) is the key enzyme responsible for transforming pyruvate to acetyl CoA, and providing important raw material for FPP biosynthesis [33
]. The level of PDH expression in Fg1 was significantly higher in Fg1 than in Fg2. In addition, the gene annotated to MVA kinase, 5′-PhosphoMVA and MVA 5-diphosphate were all significantly up-regulated in Fg1. These findings indicated that both MEP and MVA pathways were activated in Fg1, which provided more substrate for biosynthesis of FPP, which is a precursor of DON.
KEGG enrichment analysis revealed that the most enriched pathway was biosynthesis of secondary metabolites. The expression level of secondary metabolism-related proteins was significantly different in the two strains as demonstrated by the levels of 4-diphosphocytidyl-2-C-methyl-D-erythritolkinase (CMK, spot 35) and terpenoid synthase (TPS, spot 37), Figure 2
F. CMK, one of the key enzymes involved in natural terpenoid biosynthetic pathway, can trigger 4-(5-pyrophosphate cytidine)-2-C-methyl-D-erythritol derivative phosphate to generate 4-(5-pyrophosphate cytidine)-2-C-methyl-D-erythritol 2-phosphate [34
]. Therefore, it regulates the synthesis of terpene compounds.
Terpene synthase is a key enzyme associated with “carbon flux”, which controls terpene biosynthetic pathway, and it can catalyze the conversion of a single substrate to different terpene products [35
]. Internal TPS can catalyze FPP molecular carbon chain cyclization to form a ring of different terpenoids or intermediates, through various enzymatic modification, such as isomerization, hydroxylation, oxidation, and reduction to form different structural and functional terpenoid derivatives.
DON biosynthesis requires a series of oxidation-reduction reactions. The expression level of FAD monooxygenase (FADMO) in Fg1 was significantly higher than that in Fg2. FADMO known as a hydroxylase, is an oxidoreductase based on blood-red knot sulfur salt, which is an active center for the catalyzation of oxygen atoms. It has been shown that FADMO produced by F. verticillioides can catalyze Baeyer-Villiger oxidation of steroidal compounds to generate lactone compounds. FADMO is also involved in the formation of various important substances, which is closely related to secondary metabolism, in fungi.
A total of 898 DEGs (|log2 (Fold Change)| > 1) were noted, of which 563 (62.7%) were up-regulated, and 335 (37.3%) were down-regulated. The result indicated significant differences in gene expression profile of Fg1 and Fg2, thereby revealing their phenotypes considering DON-production. The findings revealed eight genes related to DON biosynthesis, and their expression levels were verified by qPCR. The expression level of 7 out of 8 genes was higher in Fg1 than in Fg2. All these genes belonged to TRI
cluster which is responsible for DON synthesis in F. graminearum
. Most of the TRI
were poorly expressed in Fg2 demonstrating the reason for no DON production in Fg2. In addition, STPK and STPK-Cek1 belonged to MAPKs that positively regulate DON biosynthesis in F. graminearum
]. Both of them were significantly up regulated in Fg1. The transcription factor, Atf1, negative regulates DON synthesis, and Van-Nguyen et al. [28
] reported that DON production in FgAtf1
-deficient mutants was 5-fold more than that in wild-type strains in vitro. Our results indicated that DON biosynthesis was regulated not only by TRI
genes, but also by protein kinases, in Fg1.
5. Materials and Methods
5.1. Strains, Media and Culture Conditions
Strains were acquired by the following method. Briefly, the wheat with Fusarium head blight was collected and treated with 0.1% sodium hypochlorite solution for 1 min, and washed three times with sterile water. The collected wheat was inoculated on Bengal red medium (BRM: 31.6 g Bengal red (Sangon Biotech Co., Shanghai, China); and add deionized water up to 1 L). Seven days after incubation at 25 °C, the spores of the growing fungal strain were detected using a microscope. Fusarium spp., which show presence of the sickle conidia was inoculated to new BRM until a pure culture was obtained. Fusarium spp. was then cultured on potato dextrose agar (PDA: extract of 200 g boiled potatoes; 20 g glucose (Sangon Biotech Co., Shanghai, China); 20 g agar (Sangon Biotech Co., Shanghai, China) add deionized water up to 1 L) at 25 °C for 7 days, then the culture was maintained at 4 °C. Fusarium spp. was grown on PDA medium at 25 °C for 7 days before use.
5.2. Screening of F. graminearum with Specific PCR
The mycelium of Fusarium
spp. growing on PDA was collected at 7 days after incubation at 25 °C and was ground to fine powder using nitrogen. Genomic DNA was extracted from all the strains using the Ezup Column Fungi Genomic DNA Purification Kit (Sangon Biotech, Co., Shanghai, China) according to the manufacturer’s instructions. F. graminearum
specific primers—Fg16F (forward): 5′-CTCCGGATATGTTGCGTCAA-3′ and Fg16R (reverse): 5′-GGTAGGTATCCGACATGGCAA-3’ [36
] were used to identify the seven strains. PCR was performed as follows: 2 μL DNA template (~50 µg), 2.5 μL 10X rTaq PCR buffer (Mg2+
plus), 2.5 μL dNTPs (2.5 μM each), 2.5 µL each primer (0.5 µM each), 0.2 μL rTaq DNA polymerase (TAKARA, Tokyo, Japan), and sterile water up to 25 μL. The conditions for the PCR amplification assay were: 94 °C for 5 min; 32 cycles at 94 °C for 1 min, 54 °C for 1 min, and 72 °C for 1 min; and 72 °C for 10 min. The ITS region of the two strains, Fg1 and Fg2, which were screened using the specific primer pair, Fg16F and Fg16R, were then identified by primers ITS1: 5′-TCCGTAGGTGAACCTGCG-3′ and ITS4: 5′-TCCTCCGCTTATTGATATGC-3′ [37
]. PCR was performed as mentioned above. The PCR results were determined using agarose gel (1% w
) electrophoresis. The PCR product was sequenced and the sequences were subjected to BLAST analysis using NCBI nr database [38
]. These sequences homologous to Fg1 and Fg2 were obtained. These homologous sequences were clustered by clustalW and phylogenetic tree was built using MEGA5.0.
5.3. DON Extraction and HPLC-UV Analysis
DON was extracted using ethyl acetate. Briefly, the strains, which were screened by the specific primer pair, Fg16F and Fg16R, were activated on Czapex yeast agar (CYA) (100 mL: 0.5 g Yeast extract, 0.1 g K2HPO4, 0.05 g MgSO4·7H2O, 0.05 g KCl, 0.001 g FeSO4, 3 g sucrose, 2 g agar) by incubation for 7 days at 25 °C. Then, the mycelia were inoculated into 50 mL 3% Mung Bean Soup (MBS) medium (1 L: 300 mL extract of 30 g boiled Mung Bean, 700 mL ddH2O) at 25 °C, and were shaking conditions at 180 rpm. At 3 days post inoculation, the spores were collected by centrifugation and washed three times with sterile water. One milliliter spores at a density of 1 × 105 cells/mL were inoculated into 100 mL Czapex yeast broth medium (CYB) (100 mL: 0.5 g Yeast extract, 0.1 g K2HPO4, 0.05 g MgSO4·7H2O, 0.05 g KCl, 0.001 g FeSO4, 3 g Sucrose) and cultured at 25 °C, under shaking conditions at 180 rpm. At 15 days after incubation, the supernatant of the cultures was collected by centrifuging at 10,000 rpm for 10 min at 4 °C (Eppendorf, Hamburg, Germany). Then, ethyl acetate at three times the volume of the supernatant was added and mixed for 10 min. After standing for 10 min, the organic phase, which contained ethyl acetate was collected and the residue was extracted again with ethyl acetate. All the organic phase was collected and evaporated using vacuum rotary evaporator RE 2000E (Yarong, Shanghai, China) at 40 °C, 0.1 Mpa, 120 rpm. The residue was dissolved in methanol. DON was purified by deoxynivalenol immunoaffinity column IAC-030-3 (Pribolab, Qingdao, China) following the manufacturer's instructions. A high-performance liquid chromatography system Agilent 1260 (Agilent, Santa Clara, CA, USA) was used to quantify DON. The analytical column used was Zorbax, SB-C18 250 × 4.6 mm 5 μm (Agilent, Santa Clara, CA, USA). The UV detection wavelength was set at 218 nm and the column temperature was held at 35 °C. All the samples were filtered through a 0.22 μm Wondadisc NY organic filter (SHIMADZU, Kyoto, Japan) before use. Twenty microliter of sample was injected to the HPLC system. Acetonitrile and water (16:84, v/v) was used as the mobile phase and the flow rate was 1 mL/min. Data was collected and analyzed using Gilson Unipiont software 5.0 (Gilson, Inc., Middleton, WI, USA).
5.4. Proteome Analysis
5.4.1. Protein Sample Preparation
Each of three biological replicates were used to performed proteome analysis. As shown in DON analysis, 1 mL F. graminearum
spore at a density of 1 × 105
cells/mL was inoculated into 100 mL CYB and incubated at 25 °C, under conditions at 180 rpm. After 15 days, the mycelia were filtered using 100 mesh sieve, washed thrice with cold distilled water, and centrifuged at 10,000 rpm for 15 min (4 °C) every time. The mycelia were collected and then ground into fine powder by mortar using nitrogen. Thereafter, the powder was transferred and 10 mL protein extraction buffer (10 mM Tris-HCL, 1 mM EDTA, pH 8.0), 1 mM PMSF, 50 μg RNase A and 200 μg DNase were added. The mixture was oscillated and mixed well and then incubated in ice for 30 min (the mixture was shaken every 10 min). The samples were centrifuged at 10,000 rpm for 15 min (4 °C), and then the supernatant was collected. Three volumes of 20% trichloroaceticacid (TCA)/acetone that were pre-cooled at −20 °C were added to the supernatant, mixed and incubated at −20 °C for 12–16 h. Further, the sample was centrifuged at 15,000 rpm for 20 min (4 °C) and the pellets was collected. The pellets was washed three times with acetone (pre-cooled at −20 °C) and centrifuged at 15,000 rpm for 10 min (4 °C) every time. The pellets was air-dried on ice, and solubilized in lysis buffer (2 M thiourea, 7 M urea, 4% (w
) 3-[(3-Cholamidopropyl)dimethylammonio] propanesulfonate (CHAPS) (Bio-Rad, Hercules, CA, USA), 18 mM dithiothreitol (DTT) and 0.5% Ampholyte (Bio-Lyte) (v
, pH 3–10)). The protein concentration was determined by Bradford’s method [39
], and, the protein samples were stored at −80 °C until use.
5.4.2. Two-Dimensional Gel Electrophoresis and Image Analysis
Two-dimensional gel electrophoresis was performed as described by Wang et al. [40
] with some modifications. A 24-cm IPG strip (GE Healthcare, Piscataway, NJ, USA) was used to perform the first dimension electrophoresis. First, protein samples were diluted to 3 mg/mL using rehydration solution (2 M thiourea, 7 M urea, 4% (w
) CHAPS, 18 mM DTT, 0.5% (v
) Bio-Lyte (pH 3–10)). Four hundred and fifty microliters (1.35 mg) of the diluted protein sample was added to the IPG-box (GE Healthcare, Piscataway, NJ, USA) and the gel side of the strips was covered on the protein sample. After 14 h incubation at room temperature, the rehydrated strips were used to perform isoelectric focusing and were then equilibrated by two steps with two equilibration solution (50 mM Tris-HCl buffer, 6 M urea, 20% (v
) glycerol and 2% (w
) SDS supplemented with 2% (w
) DTT, and 2.5% (w
) iodoacetamide, respectively. During each step, the incubation was done under room temperature at 120 rpm for 15 min. The second dimension was electrophoresed on 12.5% polyacrylamide gel using an Ettan DALT System (GE Healthcare, USA). Marker protein was added to the ‘+’ side to evaluate the molecular mass of proteins. Electrophoresis conditions were as follows: 60 voltage for 1.5 h followed by 275 voltage for 4 h. After electrophoresis, the gels were visualized using Coomassie Blue stain (1 L: 450 mL methanol, 450 mL ddH2
O, 100 mL glacial acetic acid and 2.5 g R250). The stained gels were scanned and analyzed using Image Master 7.0 analysis software (GE Healthcare, Piscataway, NJ, USA). Protein with an average fold change >2, p
-value < 0.05, and exhibiting the same expression pattern among the three replicates were considered as significantly differentially expressed proteins.
5.4.3. In-Gel Digestion
Differentially expressed proteins were collected from the gel, washed twice for 15 min using 350 μL distilled H2O, and destained with 100 μL 50 mM NH4CO3/50% acetonitrile. Ten millimolar DTT was added to the gel to reduce the proteins under 55 °C for 45 min. Then, 55 mM iodoacetamide was added to alkylate the protein at room temperature for 45 min. Acetonitrile (50%)/0.025 mM NH4HCO3 was added to wash the protein, which was further dried on ice. The dried proteins were incubated overnight at 37 °C in 10 μL 10 ng/mL trypsin (Sigma-Aldrich, St. Louis, MO, USA). The supernatant was collected for MS analysis.
5.4.4. MS Analysis and Database Query
MS analysis was performed as described by Zhang et al. [41
] and Zheng et al. [42
] with some modifications. Each protein solution was mixed with an equal volume of matrix solution (70% acetonitrile, 0.1% trifluoroacetic acid, 10 mg/mL α-cyano-4 hydroxycinnamic acid). Mass spectra were analyzed using MALDI-TOF mass spectrometer (BrukerDaltonics, Bremen, Germany). Sequence query using peptide mass values and corresponding fragment peak lists were used to search for protein sequences against the NCBInr and Swissport databases using MASCOT version 2.3 software (Matrix Science, Franklin, UK) with the following search parameters: taxonomy, all series, allowed modifications, carbamidomethyl of cysteine (fixed), oxidation of methionine (variable), peptide tolerance, ±0.3 Da. The highest MOWSE score was only considered as the most probable identification, and was significant (p
< 0.05) when protein scores were >88 (NCBInr) or 70 (Swissport).
5.5. Transcriptome Analysis
5.5.1. RNA Extraction and Quality Test
F. graminearum was cultured in CYB as described above. At 15 days after inoculation, the mycelia were collected and fine ground to powder using a mortar and pestle with liquid nitrogen. Total RNA was extracted using the fungal total RNA isolation kit (Sangon Biotech Co., Shanghai, China) following the manufacturer's instructions. RNA degradation and contamination was monitored on 1% agarose gels and the RNA purity was detected by NanoPhotometer® spectrophotometer (IMPLEN, München, Germany). RNA concentration was measured using Qubit® RNA Assay Kit in Qubit® 2.0 Flurometer (Life Technologies, Carlsbad, CA, USA). RNA integrity was assessed using the RNA Nano 6000 Assay Kit of the Bioanalyzer 2100 system (Agilent Technologies, Santa Clara, CA, USA). The samples that meet the requirements were used for the next steps.
5.5.2. RNA-Seq Library Construction and Sequencing
Each one RNA sample of Fg1 and Fg2 was used to perform RNA-seq. Three microgram RNA of each sample was used for preparing libraries. Sequencing libraries were generated using NEBNext Ultra RNA Library Prep Kit for Illumina (NEB, Ipswich, MA, USA) following manufacturer’s instructions and four index codes were added to attribute sequences of each sample. Briefly, mRNA was purified from total RNA using poly-T oligo-attached magnetic beads (Life Technologies, Carlsbad, CA, USA), and then fragmented using divalent cations under elevated temperature in NEBNext First Strand Synthesis Reaction Buffer (5X). Random hexamer primer and M-MuLV Reverse Transcriptase (RNase H) was used to synthesize the first strand cDNA. DNA Polymerase I and RNase H was subsequently used to synthesize the second strand cDNA. Exonuclease/polymerase was used to convert remaining overhangs into blunt ends. NEBNext Adaptor were ligated to prepare for hybridization after adenylation of 3′ ends of DNA fragments. The library fragments were purified with AMPure XP system (Beckman Coulter, Beverly, MA, USA) for selecting cDNA fragments of preferentially 150~200 bp in length. cDNA (size-selected and adaptor-ligated) was incubated with 3 μL USER Enzyme (NEB, Ipswich, MA, USA) at 37 °C, 15 min, followed by at 95 °C for 5 min. Then PCR was performed with Phusion High-Fidelity DNA polymerase, Universal PCR primers and Index (X) Primer. PCR products were purified by AMPure XP system and library quality was assessed using Agilent Bioanalyzer 2100 system. The clustering of the index-coded samples was performed on a cBot Cluster Generation System using the TruSeq PE Cluster Kit v3-cBot-HS (Illumia) according to the manufacturer’s instructions. RNA-seq libraries were sequenced on an Illumina HiSeq 2000 platform to generate 125 bp/150 bp single-ended reads.
5.5.3. Bioinformatics Analysis of RNA-Seq Data
Raw reads were pre-processed to obtain the clean reads by removing reads containing ploy-N, reads containing adapter and low quality reads from raw data. Q20, Q30 and GC content of the clean data were assessed, Table S1
. The clean data with high quality was used to perform all the downstream analyses. TopHat v2.0.12 can generate a database of splice junctions based on the gene model annotation file, which was used to align the paired-end clean reads to the reference genome of F. graminearum
PH-1 (taxid: 229533) [43
]. HTSeq v0.6.1 was used to count the reads numbers mapped to each gene [44
]. Then, the number of fragments per kilobase of transcript sequence per millions base pairs sequenced (FPKM) of each gene was calculated based on the length of the gene and reads count mapped to this gene. FPKM was used to estimate the gene expression levels [45
]. edgeR program package was used to adjust the read counts with one scaling normalized factor for each sequenced library. DEGSeq R package (1.20.0) was used to analyze the differential expression in two samples. Benjamini and Hochberg method were used to adjust the p
]. |log2 (Fold change)| > 1 and corrected p
< 0.005 were considered significantly differential expression. The gene expression level in Fg1 and Fg2 from transcriptome data was shown in Supporting Information, S1
5.5.4. GO and KEGG Pathway Enrichment Analysis
GOseq R package was used to perform GO enrichment analysis of DEGs [47
]. GO terms with corrected p
< 0.05 were considered significantly enriched. The statistical enrichment of differential expression genes in KEGG pathways was tested by the KOBAS software.
The RNA used for quantitative reverse transcription PCR (qRT-PCR) analysis was extracted as described above. RNA extraction was performed from independently generated Fg1 and Fg2 samples on CYB at 15 days after incubation at 25 °C, under shaking condition at 180 rpm. Primers for qRT-PCR were designed using the Primer 6 software and synthesized by Sangon Biotech. cDNAs were acquired by reverse transcription from 1 μg total RNA using PrimeScriptRT reagent Kit with gDNA Eraser (TAKARA, Tokyo, Japan) manufacturer’s protocol. qRT-PCR analysis was performed on ABI 7300 Real-Time PCR System (Applied Biosystems, Foster City, CA, USA) using the SYBR Premix Ex Taq II Tli RNaseH Plus (TAKARA, Tokyo, Japan) and following the manufacturer’s protocol. EF1A
gene was used as an internal control to normalize the expression data [48
]. qRT-PCR experiment was repeated three times, each sample having three technique replicates. The relative expression level of genes was calculated using the 2−ΔΔCT
] and standard deviation was calculated between three biological replicates. The gene specific primers are listed in Supporting Information Table S3
5.7. Statistical Analysis
The data were analyzed by the analysis of variance (ANOVA) using the statistical program SPSS/PC version II.x, (SPSS Inc. Chicago, IL, USA) and the Duncan’s multiple range test was used for separation of means. The statistical significance was applied at the level p < 0.05.