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高温胁迫不仅导致植物表型的变化,而且会引起植物体内细胞稳态失衡,生长发育受到抑制,严重影响观赏植物的品质[1]。环境温度的变化对植物光合作用的多种生理生化过程有直接的影响,包括光合碳固定和还原、蔗糖合成、光合产物的运输与分配等[2]。碳同化是光合作用中植物在同化力形成之后的第3个阶段,此阶段中,植物叶绿体基质中的Rubisco酶利用ATP和NADPH同化二氧化碳(CO2)生成淀粉、蔗糖、葡萄糖、果糖等物质。在高等植物光合作用中,果糖-1,6-二磷酸酶(Fructose-1, 6-diphosphate synthase, FBPase)在卡尔文循环和细胞质中的蔗糖生物合成途径中都起着关键作用,其中存在至少2种酶:叶绿体型FBPase和胞质型FBPase。叶绿体型FBPase主要参与还原磷酸戊糖途径,同时参与叶绿体中淀粉的合成;胞质型FBPase主要参与糖异生途径和蔗糖的合成,在蔗糖的合成中起着重要的调节作用[3-4]。有研究指出蔗糖磷酸合酶(sucrose diphosphate synthase, SPS)与淀粉积累呈现负相关关系,而与蔗糖形成呈正比关系[5-6],并与蔗糖合成酶(sucrose synthase, SS)一起成为蔗糖调节的关键酶[7],为淀粉合成提供底物及能量。淀粉是植物体中碳水化合物的主要储存形式,叶片中淀粉合成是一个动态的过程[8]。在淀粉合成通路中,腺苷二磷酸葡萄糖焦磷酸化酶(ADP-glocose pyrophosphorylase, AGP)作为限速酶,参与第一步反应,颗粒结合淀粉合酶(granule-bound starch synthase, GBSS)参与直链淀粉合成,可溶性淀粉合成酶(soluble starch synthase, SSS)和淀粉分支酶(starch branching enzyme, SBE)协作合成支链淀粉[7]。这些碳同化产物既是光合作用的产物,同时还是植物呼吸作用的底物,为植物的生长发育提供碳骨架的同时,还可增强植物的抗逆性。为进一步了解植物对高温的响应,分子生物学与转录组学等应用与解析调控植物耐热的分子基础,培育了相关观赏植物品种[1]。
景宁木兰Magnolia sinostellata是木兰科Magnoliaceae木兰属Magnolia灌木,早春开花,花色浅粉色到粉红色,具有较高的观赏价值,具有开发应用价值[9]。全球变暖带来的极端高温可能对景宁木兰的生长发育带来潜在的威胁。目前已挖掘了景宁木兰热胁迫下实时荧光定量PCR 内参基因,但还未深入研究。因此,本研究以景宁木兰幼苗为对象,采取高温胁迫处理,研究其糖代谢途径变化机制,从而探究景宁木兰对高温的响应情况,同时为木兰属植物的城市应用奠定基础。
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与对照相比,高温胁迫下24和48 h时景宁木兰的果糖、葡萄糖和蔗糖质量分数增加(图1A~C),除高温胁迫24 h的葡萄糖质量分数与对照无显著差异外(图1B),其他均呈显著差异(P<0.05)。与对照相比,高温胁迫24 h时的淀粉质量分数显著降低(P<0.05),而胁迫48 h时的淀粉质量分数显著升高(P<0.05)(图1D)。FBPase和SPS是蔗糖合成的关键酶,与对照相比,FBPase活性在胁迫24 h时先显著升高(P<0.05),在48 h时下降,但差异不显著(P>0.05)(图1E)。在高温胁迫下,SPS活性相比对照在24 h下降,48 h时有所上升,但并无显著差异(P>0.05)(图1F)。相关性分析结果表明(表1):蔗糖与果糖变化成极显著正相关(P<0.01),淀粉、SPS活性与FBPase活性成负相关。
图 1 不同热胁迫处理对景宁木兰碳水化合物同化过程的影响
Figure 1. Effects of different heat stress treatments on the carbohydrates assimilation process of M. sinostellata
表 1 高温胁迫下景宁木兰碳水化合物质量分数与酶活性的相关系数
Table 1. Correlation coefficient between carbohydrate contents and enzyme activities of M. sinostellata under high temperature stress
指标 果糖 葡萄糖 蔗糖 淀粉 FBPase活性 SPS活性 果糖 1 葡萄糖 0.945 1 蔗糖 0.999** 0.937 1 淀粉 0.697 0.853 0.670 1 FBPase活性 0.261 0.030 0.298 −0.493 1 SPS活性 0.707 0.738 0.680 0.891 −0.432 1 说明:**表示差异极显著(P<0.01) -
转录组数据(表2)显示:测序碱基对总数为7 054万~ 7 313万条 。每个原始读取从一端测序,长度为50 bp。去除低质量序列后(即含有<1%的不确定碱基),各测序样本共获得70 547 818(ck-24)、72 966 866(ck-48)、73 134 592(H-24)和73 140 464(H-48) 条。每个库中clean reads的比例平均为99.53%。来自对照和高温样本的转录组都有至少7 000万个clean reads,这表明景宁木兰转录组数据质量较高,能够开展后续的生物信息学分析。数据筛选后得到的17 884个不同长度的差异unigenes[错误发生率(FDR)≤0.001, log2R≥1]。H-24与ck-24相比,4 662个基因的表达下调,6 611个基因的表达上调;H-48与ck-48相比,4 658个基因的表达下调,5 131个基因的表达上调;H-48与H-24相比,4 548个基因的表达下调,4 056个基因的表达上调(表3)。
表 2 高温胁迫和非高温胁迫下景宁木兰的叶片测序结果与参考基因序列的对比率
Table 2. Ratio of leaf sequencing results to reference gene sequences of M. sinotellata under heat stress and non-heat stress
处理 总读数 总碱基对 总比对数 高质量比对数 丢失对比数 单一比对数 非单一读数 总未比对读数 ck-24 70 547 818
(100)7 054 781 800
(100)52 601 172
(74.56)33 257 776
(47.14)19 343 396
(27.42)38 336 892
(54.34)14 264 280
(20.22)17 946 644
(25.44)ck-48 72 966 866
(100)7 296 686 600
(100)55 252 592
(75.72)35 172 380
(48.20)20 080 212
(27.52)39 734 140
(54.46)15 518 452
(21.27)17 714 272
(24.28)H-24 73 134 592
(100)73 134 592 009
(100)52 733 028
(72.10)33 645 473
(46.00)19 087 555
(26.10)38 257 910
(52.31)14 475 118
(19.79)20 401 562
(27.90)H-48 73 140 464
(100)7 314 046 400
(100)54 165 208
(74.06)34 404 377
(47.04)19 760 831
(27.02)40 219 158
(54.99)13 946 050
(19.07)18 975 254
(25.94)说明:括号内为参考基因序列的对比率(%) 表 3 差异表达基因统计
Table 3. Statistic of differentially expressed genes
总计 ck-24/H-24 ck-48/H-48 H-24/H-48 上调 6611 5131 4056 下调 4662 4958 4548 -
GO数据库定义了3类系统来描述基因产物的具体功能:生物过程(biological process)、细胞组分(cellar component)和分子功能(molecular function),这些基因又被具体分为56个小类,从而发挥生物功能。将组装的景宁木兰unigene与GO数据库比对分析,图2A~C显示:景宁木兰序列中有81 573条unigene可以进行功能分类。其中33.03%的基因显著富集于生物过程、34.31%的富集于细胞组分,32.66%的分子功能。生物学过程中的主要途径是细胞途径和代谢过程相关的转录调控,细胞组分中最多的是膜的构成,分子功能中最多的是结合和催化活性。
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将组装的景宁木兰unigene与KEGG数据库比对及KEGG富集分析(图2D~E),结果发现:在景宁木兰高温胁迫的3个比较组中,ck-24与H-24、H-24与H-48代谢相关通路高度富集;ck-24与H-24、ck-48与H-48淀粉和蔗糖代谢通路富集排名第3位,H-24与H-48排名第4位。这些结果表明:淀粉和蔗糖代谢途径在景宁木兰高温胁迫响应机制中具有重要作用。
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在淀粉代谢通路中共有105个差异基因。在该通路中,8个DEGs调控ADP-glucose以促进淀粉酶合成,5个DEGs调控淀粉酶以生产淀粉;淀粉也可以通过同样的途径调控ADP-glucose产生α-D-Glucose-1P,然后再形成UDP-glucose,UDP-glucose再在蔗糖合成酶基因和蔗糖6磷酸合成酶基因的作用下形成蔗糖;蔗糖代谢通路中有17个差异基因,其中有6个属于蔗糖合酶基因,5个属于蔗糖磷酸合成酶(图3A~D)。选取6个淀粉和蔗糖代谢途径高表达基因,即GP(CL3087.contig2)、SS(Unigene40295)、Glc-1-pa(Unigene38453)、GBE(CL4668.contig3)、SUS(Unigene42760)、SPS(CL651.contig6),通过qPCR定量分析,结果显示(图4):与对照相比,高温胁迫48 h处理下淀粉和糖代谢途径上的GP(CL3087.contig2)、SS(Unigene40295)、Glc-1-pa(Unigene38453)、GBE(CL4668.contig3)基因表达显著上调(P<0.05),SUS(Unigene42760)、SPS(CL651.contig6)基因表达显著下降(P<0.05)。由此说明,在高温胁迫下,淀粉合成酶基因及蔗糖6磷酸合成酶基因表达均呈现上调的趋势,以促进蔗糖产生。
Transcriptional analysis of starch and sucrose metabolism pathways in Magnolia sinostellata under heat stress
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摘要:
目的 从分子生物学角度探究景宁木兰Magnolia sinostellata能否适应城市高温环境,为木兰属Magnolia植物城市推广应用和胁迫分子研究奠定基础。 方法 采取人工控制实验,对景宁木兰幼苗进行40 ℃极端高温处理,测定果糖、葡萄糖、蔗糖、淀粉碳同化产物,以及果糖磷酸酶、蔗糖磷酸合成酶,进行了转录组测序。 结果 随着胁迫时间的延长,景宁木兰叶片果糖、葡萄糖、蔗糖、淀粉质量分数发生一定的变化,但是差异不显著(P>0.05),果糖合成酶活性呈现显著下降趋势(P<0.05),蔗糖合成酶变化不显著(P>0.05)。转录组数据进一步揭示了在高温胁迫下,相比于24 h,48 h时景宁木兰叶片调节淀粉合成的SS(Unigene 40295)、Glc-1-pa(Unigene 38453)、GBE(CL4668.contig3)基因的表达量增加,随着高温胁迫的加深,调节蔗糖合成的SPS基因呈现下降趋势,并通过荧光定量验证了以上结果。 结论 景宁木兰对极端高温(40 ℃)有一定的短时耐受性,为应对高温胁迫,不但碳同化产物发生显著变化,调控淀粉与蔗糖代谢途径的关键基因表达也发生了变化,进一步证明了高温会导致景宁木兰叶片内蔗糖和淀粉的相互转化。图4表3参25 Abstract:Objective The purpose is to explore whether the shrub species of Magnolia sinostellata could adapt to the high temperature in the city and promote its application. Method The 1-year-old seedlings of M. sinostellata were treated with high temperature at 40 ℃ to determine the fructose, glucose, sucrose, starch carbon assimilates, fructose phosphatase, sucrose phosphate synthase, and transcriptome sequencing. Result With the extension of stress time, the contents of fructose, glucose, sucrose and starch in leaves of M. sinostellata were changed, but the difference was not significant(P>0.05). The fructose synthase was significantly decreased (P<0.05), but the sucrose synthase was not significantly changed (P>0.05). Transcriptomic data further revealed that SS (Unigene 40295), Glc-1-pa (Unigene 38453) and GBE (CL4668.contig3) regulated starch synthesis at 48 h compared with 24 h under heat stress. The expression of GBE (CL4668. contig3) gene increased, and the SPS gene that regulates sucrose synthesis decreased with the deepening of heat stress. The above results were verified by qPCR. Conclusion All results indicated that M. sinostellata had a certain short-term tolerance to extreme temperature of 40 ℃. In order to cope with high temperature stress, not only the carbon assimilates were significantly changed, but also the expression of key genes regulating starch and sucrose metabolism were changed. It was further proved that high temperature could lead to mutual conversion of sucrose and starch in the leaves of M. sinostellata. [Ch, 4 fig. 3 tab. 25 ref.] -
Key words:
- heat stress /
- carbon assimilation products /
- metabolic pathway /
- key genes /
- Magnolia sinostellata
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表 1 高温胁迫下景宁木兰碳水化合物质量分数与酶活性的相关系数
Table 1. Correlation coefficient between carbohydrate contents and enzyme activities of M. sinostellata under high temperature stress
指标 果糖 葡萄糖 蔗糖 淀粉 FBPase活性 SPS活性 果糖 1 葡萄糖 0.945 1 蔗糖 0.999** 0.937 1 淀粉 0.697 0.853 0.670 1 FBPase活性 0.261 0.030 0.298 −0.493 1 SPS活性 0.707 0.738 0.680 0.891 −0.432 1 说明:**表示差异极显著(P<0.01) 表 2 高温胁迫和非高温胁迫下景宁木兰的叶片测序结果与参考基因序列的对比率
Table 2. Ratio of leaf sequencing results to reference gene sequences of M. sinotellata under heat stress and non-heat stress
处理 总读数 总碱基对 总比对数 高质量比对数 丢失对比数 单一比对数 非单一读数 总未比对读数 ck-24 70 547 818
(100)7 054 781 800
(100)52 601 172
(74.56)33 257 776
(47.14)19 343 396
(27.42)38 336 892
(54.34)14 264 280
(20.22)17 946 644
(25.44)ck-48 72 966 866
(100)7 296 686 600
(100)55 252 592
(75.72)35 172 380
(48.20)20 080 212
(27.52)39 734 140
(54.46)15 518 452
(21.27)17 714 272
(24.28)H-24 73 134 592
(100)73 134 592 009
(100)52 733 028
(72.10)33 645 473
(46.00)19 087 555
(26.10)38 257 910
(52.31)14 475 118
(19.79)20 401 562
(27.90)H-48 73 140 464
(100)7 314 046 400
(100)54 165 208
(74.06)34 404 377
(47.04)19 760 831
(27.02)40 219 158
(54.99)13 946 050
(19.07)18 975 254
(25.94)说明:括号内为参考基因序列的对比率(%) 表 3 差异表达基因统计
Table 3. Statistic of differentially expressed genes
总计 ck-24/H-24 ck-48/H-48 H-24/H-48 上调 6611 5131 4056 下调 4662 4958 4548 -
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