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竹林金针虫是取食竹笋的叩甲幼虫的总称,虫害发生时竹笋产量显著减少,严重时竹种无法成竹,制约了竹林的自然更新[1-2]。筛胸梳爪叩甲Melanotus cribricollis隶属于鞘翅目Coleoptera叩甲科 Elateridae梳爪叩甲属Melanotus,其幼虫为中国南方早园竹Phyllostachys propinqua竹林的优势种。化学药剂防治竹林金针虫易造成环境污染、抗药性和食品安全等问题,阻碍以“生态、健康、有机”为标签的林产品产业发展,因此近年来逐渐采用生物技术防治该虫害。绿僵菌Metarhizium sp.是常见的昆虫致病真菌[3-4],对鞘翅目和鳞翅目Lepidoptera等害虫均有一定防效[5-6]。研究竹林金针虫抗绿僵菌相关基因的表达有利于深入了解害虫免疫抗性机制和虫菌互作机制,也有利于生防菌菌株改造等研究,提高其对农林害虫防治的效果。实时荧光定量聚合酶链式反应(qRT-PCR)是研究基因表达分析的关键技术,省时、高效、应用广泛;为保证目的基因定量表达结果的准确性,需引入表达稳定的内参基因作为参照[7]。内参基因又称看家基因,理想的内参基因其表达水平应在各条件下保持稳定,而实际上不同条件下许多内参基因的表达并不稳定[8-9]。因此,即使是同一物种,不同试验条件下的内参基因也不能一概而用,qRT-PCR试验之前应对所选内参基因的表达稳定性进行评估。常用的qRT-PCR内参基因包括ACT (肌动蛋白)、TUB (微管蛋白)、GAPDH (甘油醛-3-磷酸脱氢酶)、UBC (泛素结合酶)、18S rRNA (核糖体蛋白S18)、28S rRNA (核糖体蛋白S28)、EF1 (延伸因子1)、SYN1 (突触融合蛋白1)、SYN6 (突触融合蛋白6)、RPS3 (核糖体蛋白S3)、PRS20 (泛素-核糖体蛋白S20)、PRS27a (泛素-核糖体蛋白S27a)、RPL10 (核糖体蛋白L10)、RPL13α (核糖体蛋白S13α)、AK (精氨酸激酶)和V-ATPase (液泡型ATP合酶)等。符伟等[10]分析了小菜蛾Plutella xylostella候选内参基因在Bt毒素诱导时的表达稳定性,最终筛选出由PRS13、RPL32和 EF1α组成的最佳内参基因组合。冯波等[11] 筛选出最适合校正松墨天牛Monochamus alternatus化学感受组织基因表达的GAPDH和TUB内参基因组合。刘金泊[12]评价了赤拟谷盗Tribolium castaneum的候选内参基因在磷化氢诱导条件下的表达稳定性,筛选出RPS18和 RPL13α最佳内参基因组合。杨苓等[13]筛选出了适合桃蛀螟Conogethes punctiferalis不同发育时期和不同组织的基因表达研究的2组最佳内参组合(RP49和GAPDH,RPL13和RP49)。陶蓉等[14]则分别筛选出了美国白蛾Hyphantria cunea不同发育阶段、不同温度和不同组织的3组最佳内参基因(RPL12和EF1β,EF1α和GAPDH,ACT和RPS16)。目前,关于筛胸梳爪叩甲幼虫内参基因的筛选评估尚未见报道。本研究对平沙绿僵菌Metarhizium pingshaense侵染不同时期的筛胸梳爪叩甲幼虫qRT-PCR内参基因进行了筛选和评估,以期选出最佳的内参基因,为今后开展竹林金针虫等昆虫的基因表达研究提供参考。
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由图1可见:所有样品D(260)/D(280)均为1.8~2.1,凝胶电泳结果可见2条清晰条带(28S和18S rRNA),说明总RNA较为完整,未出现明显降解。
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根据筛胸梳爪叩甲幼虫的转录组测序数据,筛选出24条候选内参基因和6条目的基因的同源序列,根据普通PCR扩增结果选出条带单一的22对特异性引物,再根据qRT-PCR的引物熔解曲线、R2和扩增效率进一步筛选出6对内参基因(β-actin、GAPDH、α-tubulin、RPL13α、RPS27a和RPS3)和6对目的基因的引物。12对引物的熔解曲线均为单峰,R2为0.989~0.998,扩增效率为88.69%~112.48%,表明引物具有特异性,cDNA的质量浓度和Ct值存在明确的线性关系,引物扩增效率符合荧光定量要求(表1)。
表 1 qRT-PCR引物信息
Table 1. Informations of qRT-PCR primers
基因 引物序列 产物长度/bp 扩增效率/% R2 β-actin F:GGATACCTCTTTTGCTCTGGG,R:ATCAGGGTGTCATGGTTGG 75 112.48 0.993 GAPDH F:CTACTCATGGTCGTTACAAGGG,R:TTCTACAACGTATTCAGCTCCAG 140 101.79 0.993 α-tubulin F:GAAGCTCGTGAAGATTTGGC,R:ACCTTCGCCTTCTCCTTCTC 137 100.63 0.996 RPL13α F:CTGAGGAAGAGCGTAAGGTG,R:TCAGCACGAGCCTTTCTTAAG 145 106.97 0.990 RPS27a F:CTTGTCCTGAATCTTTGCCTTG,R:GTTCTTTTGGTAGCGTGTCATG 146 96.20 0.998 RPS3 F:CAATAGCGCACAAACCACG,R:TGTATTGGGTGAAAAGGGAAGG 128 111.93 0.992 PGRP F:TGTCGTACTTCTGGCTATCATTG,R:TGTGATGGAGGGTTTACTTGC 123 88.69 0.989 Prx F:CTATCCCTTAGACTTCACCTTCG,R:ATTTCTCCCAAACCTCCCTG 171 106.67 0.996 SDR(1) F:CGGCATTGACGGAAACTTTAC,R:GGTTTCCACAGACTTTTGCG 126 109.16 0.995 SDR(2) F:AGGTGCTAGTTCGGGAATTG,R:CGTGTAATTTGCCAGGTTTTCC 140 99.49 0.997 SDR(3) F:GGATTACGAGCATAAGTCCTGG,R:CGGCGATGTCTTCAGATTTTAAC 126 106.58 0.996 SDR(4) F:TTAGGGTTTCAGTCAAGGCAG,R:GAAGCCGTCCAAGATATGAAAG 148 93.34 0.994 -
不同平沙绿僵菌侵染处理时长(0、7、12和17 d)下,筛胸梳爪叩甲幼虫6个候选内参基因的Ct值为11.110~15.463(图2),表明本试验条件下所选内参基因表达水平较高。但不同基因的Ct值存在差异,其中β-actin最低,平均Ct值为11.622;α-tubulin最高,平均Ct值为14.712;GAPDH的Ct值跨度最小(13.273~13.873);RPS3跨度最大(13.720~14.970)。
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GeNorm软件计算基因的表达稳定度(M值),M>1.5的内参基因不可用,M越小,内参基因的表达越稳定。该软件分析结果显示:6个候选内参基因的M值均<1.5,PRS27a和RPS3的表达最稳定,其后依次是α-tubulin、RPL13α和β-actin,GAPDH的表达最不稳定。NormFinder通过比较样本的组内变异和组间变异来评估基因的稳定值。该软件分析结果显示:RPL13α的表达最稳定,其后依次是α-tubulin、RPS3、RPS27a和β-actin,GAPDH的表达最不稳定。BestKeeper是以标准差和P来判断内参基因是否可用。该软件分析结果显示:所有候选内参基因的标准差均<1,但β-actin和GAPDH P>0.05,不适合作为本试验条件下的内参,其余4个内参基因可用。综合3个软件的评价结果发现:RPS3、PRS27a、RPL13α和α-tubulin这4个内参的表达稳定性排名稍有差异,RPS3的表达最稳定,PRS27a和RPL13α次之,随后是α-tubulin(表2)。GeNorm软件通过判断配对变异值(<0.15)来确定内参基因最佳数目。由表3可知:V2/3=0.084<0.15,表明该条件下最佳内参基因的数目n=2(表3)。
表 2 利用BestKeeper软件评价候选内参基因的表达稳定性
Table 2. Stability of candidate reference genes based on BestKeeper analysis
基因 GeNorm NormFinder BestKeeper 稳定值 排名 稳定值 排名 标准差 P 排名 β-actin 0.391 4 0.244 5 0.27 0.313 6 GAPDH 0.426 5 0.293 6 0.16 0.261 5 α-tubulin 0.242 2 0.177 2 0.24 0.042 4 RPL13α 0.319 3 0.164 1 0.32 0.024 3 RPS27a 0.197 1 0.206 4 0.35 0.012 2 RPS3 0.197 1 0.202 3 0.39 0.002 1 表 3 内参基因的最佳数量评估
Table 3. Determination of the optimal number of reference genes for normalization
Vn/n+1 配对变异值 Vn/n+1 配对变异值 V2/3 0.084 V4/5 0.092 V3/4 0.092 V5/6 0.074 说明:n表示内参基因数目 -
综合3款软件的内参基因表达稳定性排名和最佳组合数目分析结果,本研究选择PRS27a和RPS3为内参基因。由图3可知:以PRS27a和RPS3为内参基因时,6个目的基因在平沙绿僵菌不同处理时间(0、7、12和17 d)的筛胸梳爪叩甲幼虫中的表达变化趋势相同;其中,PGRP基因相对表达量在7 d时都较对照(0 d)显著提高(P<0.05),随后下降,12 和17 d时无显著差异;Prx基因相对表达量整体呈上升趋势,在12 和17 d时均显著高于对照(P<0.05);SDR(1)相对表达量则呈下降趋势;SDR(2)在17 d 时相对表达量显著升高(P<0.05);SDR(3)和SDR(4)相对表达量均先升高后下降,并在12 d时表达量最高,较其他处理时间存在显著性差异(P<0.05)。
Screening and application of reference genes for qRT-PCR in bamboo wireworm
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摘要:
目的 筛选平沙绿僵菌Metarhizium pingshaense侵染条件下筛胸梳爪叩甲Melanotus cribricollis幼虫稳定表达的内参基因,为该竹林金针虫相关基因的表达研究奠定基础。 方法 基于筛胸梳爪叩甲幼虫的转录组数据,利用实时荧光定量PCR扩增特异性引物,分析相关性和扩增效率;利用GeNorm、NormFinder和BestKeeper软件评估筛选出6个候选内参基因(β-actin、GAPDH、α-tubulin、RPL13α、RPS3、RPS27a),并验证其表达稳定性。 结果 GeNorm分析结果显示:PRS27a和RPS3的表达最稳定,随后依次是α-tubulin、RPL13α、β-actin和GAPDH;最适合的内参基因数目为2。NormFinder分析结果显示:RPL13α的表达最稳定,随后依次是α-tubulin、RPS3、RPS27a、β-actin和GAPDH。BestKeeper分析结果显示:β-actin和GAPDH的P>0.5,不适合作为本试验条件下的内参基因。不同软件分析得出的候选内参排序存在一定差异。综合分析和表达稳定性验证表明PRS27a或RPS3是最佳内参基因,6个目的基因的表达水平变化趋势均基本一致。 结论 PRS27a和RPS3是研究平沙绿僵菌侵染的竹林金针虫相关基因表达的最佳内参基因。图3表3参27 Abstract:Objective The objective of this study was to screen the stable expression of internal reference genes of Melanotus cribricollis larvae infected by Metarhizium pingshaense, so as to lay a foundation for the research on related gene expression in this bamboo wireworm. Method Based on the transcriptome data of M. cribricollis larvae, the correlation (R2) and amplification efficiency were analyzed by qRT-PCR with specific primers. The 6 candidate reference genes including β-actin, GAPDH, α-tubulin, RPL13α, RPS3 and RPS27a were evaluated by GeNorm, NormFinder and BestKeeper softwares. The stabilities of selected candidate reference genes including PRS27a and RPS3 were further validated by analyzing the expression of 6 target genes. Result GeNorm analysis showed that the expression of PRS27a and RPS3 were the most stable, followed by α-tubulin, RPL13α, β-actin and GAPDH. The most suitable number of internal reference genes was 2. NormFinder analysis showed that the expression of RPL13α was the most stable, followed by α-tubulin, RPS3, RPS27a, β-actin, and GAPDH. BestKeeper analysis showed that the P values of β-actin and GAPDH were >0.5, which were not suitable for reference genes under the condition of this experiment. There were some differences in the ranking of candidate internal parameters obtained by different software analysis. Comprehensive analysis and expression stability verification showed that PRS27a or RPS3 were the best internal reference genes, and the expression levels of 6 target genes were basically the same. Conclusion PRS27a and RPS3 were the most appropriate reference genes for qRT-PCR analysis in bamboo wireworm infected by M. pingshaense. [Ch, 3 fig. 3 tab. 27 ref.] -
表 1 qRT-PCR引物信息
Table 1. Informations of qRT-PCR primers
基因 引物序列 产物长度/bp 扩增效率/% R2 β-actin F:GGATACCTCTTTTGCTCTGGG,R:ATCAGGGTGTCATGGTTGG 75 112.48 0.993 GAPDH F:CTACTCATGGTCGTTACAAGGG,R:TTCTACAACGTATTCAGCTCCAG 140 101.79 0.993 α-tubulin F:GAAGCTCGTGAAGATTTGGC,R:ACCTTCGCCTTCTCCTTCTC 137 100.63 0.996 RPL13α F:CTGAGGAAGAGCGTAAGGTG,R:TCAGCACGAGCCTTTCTTAAG 145 106.97 0.990 RPS27a F:CTTGTCCTGAATCTTTGCCTTG,R:GTTCTTTTGGTAGCGTGTCATG 146 96.20 0.998 RPS3 F:CAATAGCGCACAAACCACG,R:TGTATTGGGTGAAAAGGGAAGG 128 111.93 0.992 PGRP F:TGTCGTACTTCTGGCTATCATTG,R:TGTGATGGAGGGTTTACTTGC 123 88.69 0.989 Prx F:CTATCCCTTAGACTTCACCTTCG,R:ATTTCTCCCAAACCTCCCTG 171 106.67 0.996 SDR(1) F:CGGCATTGACGGAAACTTTAC,R:GGTTTCCACAGACTTTTGCG 126 109.16 0.995 SDR(2) F:AGGTGCTAGTTCGGGAATTG,R:CGTGTAATTTGCCAGGTTTTCC 140 99.49 0.997 SDR(3) F:GGATTACGAGCATAAGTCCTGG,R:CGGCGATGTCTTCAGATTTTAAC 126 106.58 0.996 SDR(4) F:TTAGGGTTTCAGTCAAGGCAG,R:GAAGCCGTCCAAGATATGAAAG 148 93.34 0.994 表 2 利用BestKeeper软件评价候选内参基因的表达稳定性
Table 2. Stability of candidate reference genes based on BestKeeper analysis
基因 GeNorm NormFinder BestKeeper 稳定值 排名 稳定值 排名 标准差 P 排名 β-actin 0.391 4 0.244 5 0.27 0.313 6 GAPDH 0.426 5 0.293 6 0.16 0.261 5 α-tubulin 0.242 2 0.177 2 0.24 0.042 4 RPL13α 0.319 3 0.164 1 0.32 0.024 3 RPS27a 0.197 1 0.206 4 0.35 0.012 2 RPS3 0.197 1 0.202 3 0.39 0.002 1 表 3 内参基因的最佳数量评估
Table 3. Determination of the optimal number of reference genes for normalization
Vn/n+1 配对变异值 Vn/n+1 配对变异值 V2/3 0.084 V4/5 0.092 V3/4 0.092 V5/6 0.074 说明:n表示内参基因数目 -
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