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沙棘(Hippophae rhamnoides L.)是中国重要的荒山荒坡造林、治理水土流失、改善生态环境的先锋树种[1],但干旱环境仍然限制着沙棘的生长和功能的发挥。叶片作为植株光合和蒸腾作用的重要器官,其表型变化是干旱胁迫下最为直观的重要特征。表观遗传修饰通过改变染色质状态和招募各种转录调节因子来控制基因的表达,从而影响植物对干旱胁迫等环境的响应[2]。组蛋白修饰包括组蛋白核心蛋白H2A、H2B、H3和H4的N末端特定氨基酸残基的甲基化、乙酰化、磷酸化和泛素化等[3]。组蛋白乙酰化参与染色质解缩和基因激活从而影响基因转录[4],作为一个动态可逆过程,组蛋白乙酰化和去乙酰化分别由组蛋白乙酰转移酶(HATs)和组蛋白脱乙酰酶(HDACs)催化。而HDACs已被证明在高粱(Sorghum bicolor L.)[5]、棉花(Gossypium hirsutum L.)[6]、拟南芥(Arabidopsis thaliana L.)[7]和大豆(Glycine max L.)[8]等植物中参与逆境响应和生物胁迫防御。有研究发现番茄(Solanum lycopersicum)组蛋白脱乙酰酶基因SlHDA3参与了番茄对干旱胁迫的响应,干旱胁迫和脱落酸处理显著诱导了SlHDA3的表达,沉默SlHDA3后植株对干旱胁迫的耐受性降低,干旱胁迫下脱落酸(ABA)、叶绿素、丙二醛(MDA)和脯氨酸(Pro)含量增加[9]。
曲古抑菌素A(trichostatin A, TSA) 是一种强效可逆的组蛋白去乙酰化酶抑制剂,可通过抑制HDAC而影响基因的表达[10]。研究发现TSA可以在干旱胁迫条件下显著上调花生(Arachis hypogaea L.)AhDREB1基因的表达,从而提高抗旱性[11]。在花生中组蛋白去乙酰化酶基因AhHDA1可以通过与其启动子结合来抑制AhGLK1的表达,TSA处理后AhGLK1的表达增加,H3乙酰化减少,证实AhGLK1受组蛋白去乙酰化修饰的调节[12]。在低温胁迫下,TSA处理强烈抑制了ZmDREB1和ZmCOR413等玉米(Zea mays Linn. Sp.)冷响应基因的表达[13]。另外,TSA还可以提高植物的抗寒性,并影响At1g55960、At3g50970和At5g57560等拟南芥冷诱导基因的表达[14]。
前期研究共筛选到沙棘ABF2、NAC2、C4H2、CHS4、HDA6和HDA19等干旱胁迫响应核心基因[15],揭示了以 ABA 依赖信号途径为主的信号传递途径和以类黄酮途径为主的氧自由基清除途径的耐旱分子机制[16],然而在外施TSA处理沙棘扦插苗响应干旱时,组蛋白去乙酰化酶基因表达水平的变化以及抗旱相关的ABA和类黄酮合成相关基因表达的影响不清楚。本研究探讨TSA预处理后沙棘叶片对干旱胁迫响应的表型和生理变化以及组蛋白乙酰化相关基因表达水平的变化,将为后续深入研究沙棘抗旱基因调控机制奠定基础。
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本试验使用的材料采自中国林业科学研究院沙漠林业实验中心,将引进蒙古大果沙棘‘向阳’(H.rhamnoides L. subsp. mongolica, ‘Xiangyang’, XY) 2年生扦插苗种植于中国林业科学研究院科研温室大棚,生长条件为自然光照,昼/夜温度为20~30 ℃/10~15 ℃,相对湿度在60%~70%,正常生长2个月。在试验前一周将苗木移至恒温培养箱中,设定条件为:温度为(25 ± 1) ℃,光照度为(4 500 ± 500)LX,光照时间12 h,湿度70% ± 10%,使扦插苗稳定适应环境。
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选取健康、生长均一的沙棘扦插苗带根部取出, 用1/2 Hoagland 营养液洗净土壤,洗净后的沙棘苗放在营养液中缓苗一周,之后在1 μmol·L−1 TSA(TSA, Solarbio)溶液中浸泡12 h,取部分叶片材料保存(单独TSA处理,T0),剩余沙棘苗浸泡于20%聚乙二醇(PEG6000, Solarbio)溶液中模拟土壤干旱胁迫, 分别在PEG处理12 h和48 h后取叶片材料保存(TSA + PEG复合处理,T12和T48),剩余植株取出后再分别浸泡于1/2 Hoagland 营养液正常培养3 d取叶片保存(复合处理后复水3 d处理,T12-3和T48-3)。以1/2 Hoagland 营养液正常培养植株为对照(CK)。每个分组处理均设置3次生物学重复。
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将沙棘扦插苗带根取出洗净后在1/2 Hoagland 营养液中浸泡12 h, 再转移至20% PEG 6000溶液中, 分别在PEG处理12 h和48 h后取叶片材料保存(干旱胁迫处理,Y12和Y48),剩余植株取出后再分别浸泡于1/2 Hoagland 营养液正常培养3 d取叶片保存(干旱胁迫后复水3 d处理,Y12-3和Y48-3)。以1/2 Hoagland 营养液处理为对照(CK)。每个分组处理均设置3次生物学重复。
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在每个干旱处理节点分别选取长势一致的幼苗 10 株,蒸馏水洗净滤纸吸干后用分析天平称量扦插苗鲜质量(TB)。在每个处理节点分别选取长势一致的幼苗 3株,用 LI-6400 便携式光合仪(LI-COR,美国)分别测定对照组与试验处理组沙棘幼苗叶片的净光合速率(Pn,μmol·m−2·s−1)、蒸腾速率(Tr,mmol·m−2s−1)和气孔导度(Cond,mol·m−2·s−1)。测定条件:红蓝固定光源,固定光强为1 000 μmol·m−2·s−1,温度 28 ℃,相对湿度为70%,二氧化碳浓度为温室中大气浓度。同时,使用Yaxin-1161G叶绿素荧光仪分别测量各处理幼苗叶片的PSⅡ最大光化学效率或原初光能转换效率Fv/Fm值和PSⅡ有效光化学量子产量[Y(Ⅱ)]值,使用SPAD502叶绿素含量测定仪测定叶片叶绿素相对含量(SPAD)。另外,使用脯氨酸(Pro)含量检测试剂盒(Solarbio)测定叶片游离脯氨酸含量,使用丙二醛(MDA)含量检测试剂盒(Solarbio)测定叶片丙二醛含量,使用植物脱落酸(ABA)酶联免疫分析试剂盒(Jingmeibio) 测定叶片ABA含量,使用植物类黄酮含量检测试剂盒(Solarbio)测定叶片类黄酮含量。每个分组处理均设置3次生物学重复。
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使用RNAprep Pure多糖多酚植物总RNA提取试剂盒提取沙棘幼苗叶片RNA。使用PrimeScript RT试剂盒与gDNA Eraser试剂盒进行反转录。选择干旱胁迫过程中对以脱落酸依赖信号途径为主的信号传递途径有影响的ABA合成关键基因ABF2和NAC2,对以类黄酮途径为主的氧自由基清除途径有影响的类黄酮合成关键基因C4H2和CHS4,以及组蛋白去乙酰化酶基因HrHDA6和HrHDA19-1,利用Primer 5.0软件设计引物(表1)。使用StepOnePlus RT-PCR仪器进行实时荧光定量PCR反应。以18SrRNA基因为内参,扩增程序为95 ℃预变性30 s;95 ℃变性5 s, 60 ℃退火延伸34 s, 共40个循环。基因表达量使用2−△△CT方法进行分析[17]。
表 1 沙棘内参基因和目的基因引物
Table 1. Primers for reference genes and target genes in sea buckthorn
引物名称
Primer name正向引物
Forward primer(5′→3′)反向引物
Reverse primer(5′→3′)功能注释
Functional annotation18S rRNA GCCAAGGAAGTTTGAGGCAA TTCAAAGATTACCCGGGCCT 内参基因 Reference gene ABF2 TCCAGAACACGGTGGGTAGC AAGAGTCAACGAGCCTTGCCT 脱落酸合成途径
Abscisic acid synthesisNAC2 GCTCAAAAGCCGACGACAAG CGAATTCACGCGAGGCAAAT C4H2 AACCCGAAGAGTTCCGACCA CAAGAATAGGCAAAGCCAGAATGAT 类黄酮合成途径
Flavonoid synthesis pathwayCHS4 GTCAACCTAAGTCCAAAATAACCCA CGAAGAACTGTACCTCCAGCAAA HrHDA6 GGGGGGAGCATCTTTACCAT GCTTCATTGGGTGACCTTGG 组蛋白去乙酰化酶基因
Histone deacetylase geneHrHDA19-1 GACCTCCAGACACTGACATTCCA GCTCTCCTGATCTTTAACCTCGG -
使用IBM SPSS Statistics 24 统计软件中的单因素ANOVA分析方法,计算qRT-PCR数据获得P值,P<0.05表示差异具有显著性。使用Excel软件作图。
曲古抑菌素A对沙棘扦插苗响应干旱和复水及相关基因表达的影响
Effects of Trichostatin A on Responses of Sea Buckthorn to Drought and Rehydration and Related Gene Expression
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摘要:
目的 研究组蛋白去乙酰化酶抑制剂曲古抑菌素A(Trichostatin A, TSA)在20%聚乙二醇模拟干旱和干旱后复水条件下,对沙棘扦插苗叶片形态、光合指标、脯氨酸、丙二醛和脱落酸含量等生理特性和组蛋白去乙酰化酶、合成脱落酸和类黄酮相关基因表达的影响。 方法 测定沙棘扦插苗干旱相关生理指标,实时定量PCR检测基因表达量。 结果 1 μmol·L−1TSA预处理的沙棘在同等干旱胁迫下耐旱性增强。与仅干旱处理相比,(1)叶片下垂和萎蔫程度降低,植株鲜质量下降程度更小,复水后植株恢复程度更大。(2)净光合速率、蒸腾速率、气孔导度、PSII最大光化学效率Fv/Fm值、PSII有效光化学量子产量Y(Ⅱ)值和叶绿素相对含量(SPAD)值均显著上调,复水后均下调。(3)脯氨酸和类黄酮含量显著上调,丙二醛和脱落酸含量显著下调,复水后趋势相同。(4)组蛋白去乙酰化酶基因HrHDA6和HrHDA19、脱落酸合成相关基因ABF1和NAC2表达均显著下调,类黄酮合成相关基因C4H2和CHS4表达均显著上调,复水后趋势相同。 结论 TSA通过调控沙棘扦插苗生理和基因表达参与对干旱胁迫的响应,可以提高沙棘的抗旱性,该研究为深入解析组蛋白乙酰化影响沙棘抗旱的调控机制奠定重要基础。 Abstract:Objective To study the effects of the histone deacetylase inhibitor Trichostatin A (TSA) on the physiological characteristics of leaf morphology, photosynthetic indexes, proline, malondialdehyde and abscisic acid content, synthetic histone deacetylase, abscisic acid and flavonoid-related genes of sea buckthorn cuttings under the conditions of simulated drought and post-drought rehydration of 20% polyethylene glycol. Methods The drought-related physiological indexes of sea buckthorn cuttings were measured, and the gene expression was detected by quantitative real-time PCR. Result TSA-pretreated (1 μmol·L−1) sea buckthorn was enhanced in drought tolerance under equal drought stress. Compared with the drought treatment, (1) the degree of leaf sagging and wilting reduced, the degree of fresh weight decline was smaller, and the degree of plant recovery after rehydration was greater. (2) The net photosynthetic rate, transpiration rate, stomatal conductivity, PSII maximum photochemical efficiency Fv/Fm value, PSII effective photochemical quantum yield Y(II) value and chlorophyll relative content (SPAD) value all significantly increased, and all were adjusted down after rehydration. (3) The content of proline and flavonoids increased significantly, the content of malondialdehyde and abscisic acid decreased significantly, and the trend was the same after rehydration. (4) The expression of histone deacetylase genes HrHDA6 and HrHDA19, abscisic acid synthesis-related genes ABF1 and NAC2 were significantly down-regulated, and the expression of flavonoid synthesis-related genes C4H2 and CHS4 were significantly upregulated, and the trend after rehydration was the same. Conclusion TSA can improve the drought resistance of sea buckthorn by regulating the physiological and gene expression of sea buckthorn cuttings in response to drought stress, and this study lays an important foundation for in-depth analysis of the regulatory mechanism of histone acetylation affecting sea buckthorn drought resistance. -
表 1 沙棘内参基因和目的基因引物
Table 1. Primers for reference genes and target genes in sea buckthorn
引物名称
Primer name正向引物
Forward primer(5′→3′)反向引物
Reverse primer(5′→3′)功能注释
Functional annotation18S rRNA GCCAAGGAAGTTTGAGGCAA TTCAAAGATTACCCGGGCCT 内参基因 Reference gene ABF2 TCCAGAACACGGTGGGTAGC AAGAGTCAACGAGCCTTGCCT 脱落酸合成途径
Abscisic acid synthesisNAC2 GCTCAAAAGCCGACGACAAG CGAATTCACGCGAGGCAAAT C4H2 AACCCGAAGAGTTCCGACCA CAAGAATAGGCAAAGCCAGAATGAT 类黄酮合成途径
Flavonoid synthesis pathwayCHS4 GTCAACCTAAGTCCAAAATAACCCA CGAAGAACTGTACCTCCAGCAAA HrHDA6 GGGGGGAGCATCTTTACCAT GCTTCATTGGGTGACCTTGG 组蛋白去乙酰化酶基因
Histone deacetylase geneHrHDA19-1 GACCTCCAGACACTGACATTCCA GCTCTCCTGATCTTTAACCTCGG -
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