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自噬(autophagy)是进化上保守的细胞内物质的降解途径,在真核生物中广泛存在。与其他降解系统相比,自噬最显著的特征是能降解细胞中如生物分子、细胞器甚至入侵的微生物等几乎所有的物质[1]。自噬在饥饿条件下的营养循环中起着重要作用,能将营养物质重新分配进行物质循环[2-4]。LI等[5]对玉米Zea mays研究发现:自噬在缺氮环境下调控氮回收利用以增加农作物产量;LI等[6]在谷子Setaria italica中发现:自噬相关基因SiATG8在响应氮饥饿耐受中表达上调;AVIN-WITTENBERG等[7]发现:碳饥饿条件下自噬能通过降解蛋白质等生物大分子产生氨基酸作为替代性碳源,供植物体重新利用;在碳饥饿条件下,自噬会影响中枢代谢导致拟南芥Arabidopsis thaliana ATG(autophagy-related gene)突变体表型与野生型差异明显。BARROS等[8]发现:在碳饥饿情况下,自噬中的代谢物循环和呼吸的替代途径对维持正常的呼吸功能起作用。自噬在植物体自身生长和发育中也起着重要的作用[9-10],如参与根尖的细胞生长和分化[11-12]、减数分裂后花药的发育[13]、气管元素的分化[14]、对硝酸盐的利用率[9]、对光合作用产生淀粉粒的降解[15]、在衰老叶片中叶绿体的降解[16-18]、植物体衰老过程中能量的利用[19]以及植物夜间生长供能物质的利用[20]等等。GHIGLIONE等[21]对小麦Triticum aestivum的研究发现:自噬对其小花发育过程起到作用;KURUSU等[13]对水稻Oryza sativa研究发现:自噬缺陷Osatg7和Osatg9突变体在正常生长条件下表现出完全的孢子体雄性不育和有限的花药开裂。IZUMI等[19]对水稻的研究发现:自噬可在叶片变暗引起能量限制时被激活,对其具有重要的保护作用;TOYOOKA等[22]对发芽薇甘菊Mikania micrantha种子子叶的超微结构进行观察,认为微自噬机制可能参与储备淀粉的降解;YOSHIMOTO等[23]发现:当环境中的营养供应有限时,植物细胞中的养分调动需要自噬。WANG等[15]发现:细胞自噬能够在夜间对叶片淀粉的降解起作用。有实验室证实,自噬可以在晚间为植物提供能量[20]。毛竹茎秆生长发育过程的研究分析主要在解剖结构[24]、反射光谱[25]、光合酶[26-27]、碳水化合物代谢[28-30]、蛋白质组[31]、基因组学[32-33]等方面。对模式植物拟南芥和水稻中的研究表明:自噬对植物生长起重要作用[7, 15, 19-20],而在毛竹Phyllostachys edulis中关于自噬与其快速生长关系的研究鲜见报道。本研究探讨了毛竹茎秆快速生长过程中PeATG1和PeATG4基因的表达变化,以期为毛竹快速生长内在的自噬调控机制及分子生物学基础提供参考。
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供试毛竹采自浙江省杭州市临安区(29°56′~30°23′N,118°51′~119°52′E)现代毛竹纯林示范园。该区属中亚热带季风气候,温暖湿润,四季分明,年平均气温15.8 ℃,具有春多雨,夏湿热,秋气爽,冬干冷的气候特点。全年平均日照时数1 847.3 h,年平均降水量1 628.6 mm, 无霜期234.0 d,森林覆盖率76.5%。毛竹林土壤属山地红壤,土层深度60 cm以上。
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试验材料为2018年当年生毛竹笋竹,2018年5月初,在毛竹出笋后生长至(3.0 ± 0.2)m时,分别在6个时间点(10:00、14:00、18:00、22:00、2:00、6:00)选取生境条件一致,生长状况良好,基径约15 cm自然状态下的毛竹笋竹,从茎秆地上部分的基部将其伐倒,将节间按照从基部至顶部的顺序编号(1~N)。每间隔2个节间进行取样,从基部至顶部依次选取编号为1、4、7、10、13、16、19、22的节间。取茎秆节间下部外层绿色组织,取样厚度为2 mm,用于电镜观察样品后,取下,迅速将样品放进液氮中冷冻,存于-80 ℃备用。选取3株笋竹,每株作为1个独立实验,共3次重复。
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将笋竹的第4、7、10、13节间的茎秆切成0.2 mm × 5.0 mm的小块置于体积分数2.5%戊二醛溶液中,4 ℃固定24 h。然后,将样品置于0.1 mol·L-1磷酸缓冲液(PBS, pH 7.0)中漂洗3次,15 min·次-1,再置于质量分数1%锇酸中固定2 h。之后,用PBS缓冲液漂洗3次固定材料后,使用各级梯度乙醇(体积分数30%、50%、70%、80%、90%、95%和100%)脱水处理15 min,过渡到纯丙酮处理20 min;在45 ℃下用环氧树脂(Epon 812)浸透包埋经脱水处理的材料25 h,之后在70 ℃条件下加热聚合48 h;使用LEICA EM UC7型超薄切片机修整包埋样品并切片,再分别置于柠檬酸铅溶液和醋酸双氧铀50%乙醇饱和溶液双染色10 min,在Hitachi H-65型(日本, HITACHI公司)电镜上观察,并拍照记录结果。
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基于毛竹基因组数据库中PeATG1和PeATG4的基因序列设计基因全长和定量引物,选择毛竹PeNTB基因作为荧光定量的内参基因,并使用在线网站Primer 3设计引物(http://bioinfo.ut.ee/primer3/),由有康生物科技公司合成(表 1)。
表 1 本研究所用的引物名称
Table 1. PCR primers used in this study
基因名称 序列 用途 PeATG1-F TTCTACCTCACCCCTACCGA 基因全长扩增 PeATG1-R TTCTTCTTGTTGCGCTCGAG PeATG4-F CTGTCAAGCGTTGTCGTG 基因全长扩增 PeATG4-R AACCAATAGCCAGGGATG PeATG1-F CACCGACATCATCGTCCGCTAC 荧光定量聚合酶链式反应 PeATG1-R TCGCCCTCCCGTGCCTTATC PeATG4-F ATGGCTCTTTATGTTGTTTC 荧光定量聚合酶链式反应 PeATG4-R GTGGGATGTACCTTGGAT PeNTB-F TCTTGTTTGACACCGAAGAGGAG 荧光定量聚合酶链式反应 PeNTB-R AATAGCTGTCCCTGGAGGAGTTT -
分别取适量6个时间段的毛竹笋竹茎秆第7节间,使用改良Trizol法提取茎秆组织总RNA。使用NanoDrop® ND-1000分光光度计检测样品RNA的含量与纯度,并通过质量分数1.2%琼脂糖电泳检测样品RNA的完整性。
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以上述RNA为模板,冰上配置20 μL RT-PCR体系:包括gDNA Eraser 1.0 μL,5×gDNA Eraser Buffer 2.0 μL,RT Primer Mix 1.0 μL,Prime Script RT Enzyme MixⅠ1.0 μL,5×PrimeScript Buffer 2(for Real Time)4.0 μL,总RNA 500 ng,加RNase Free dH2O至总体积20.0 μL。体系置于PCR仪中,37 ℃孵育15 min,85 ℃加热5 s。将通过反转录得到的cDNA存于-20 ℃下用于实时荧光定量分析。
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根据毛竹数据库PeATG1和PeATG4基因序列设计基因全长引物(表 1),扩增这2个基因的系列片段,扩增程序分别为:94 ℃ 5 min;94 ℃ 30 s,52 ℃ 30 s,72 ℃ 70 s,共30个循环;72 ℃ 10 min。通过质量分数1.2%琼脂糖凝胶电泳检测PCR扩增产物,送往有康生物科技公司测序。
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采用TaKaRa公司SYBR®Premix Ex TaqTM(Perfect Real Time)试剂盒,冰上配置20 μL反应体系:10 μL SYBR Premix Ex TaqTM,0.8 μL Forward Primer,0.8 μL Reverse Primer,2.0 μL反转录cDNA模版,6.4 μL灭菌蒸馏水。反应于Bio-Rad CFX manager 3.1 PCR仪上进行,采用两步法扩增标准程序:95 ℃预变性3 min,95 ℃下10 s、60 ℃下30 s,循环39次。以内参为对照,每个样品重复3次。反应完成后,得到含所有样品的记录点曲线,得出循环阈值(Ct值)。
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所有数据均为3次重复,荧光定量数据按照公式计算:相对表达量=2-∆∆Ct[34],使用内参基因校正拷贝数,利用Origin 9.0软件进行统计分析和作图。统计方法采用单因素方差分析(one-way ANOVA),对笋竹PeATG1及PeATG4基因表达量分别进行Turkey比较。
Analysis of PeATG1/PeATG4 gene expression in Phyllostachys edulis during rapid growth
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摘要:
目的 探讨毛竹Phyllostachys edulis茎秆快速生长与PeATG1和PeATG4基因表达的关系。 方法 以毛竹笋竹茎秆为材料,采用透射电镜监测笋竹快速生长期不同时间(10:00、14:00、18:00、22:00、2:00和6:00)和不同部位(第4、7、10、13节)的自噬活性,并用实时荧光定量聚合酶链式反应(qRT-PCR)分析技术测定第7节PeATG1和PeATG4基因表达量。 结果 对毛竹茎秆24 h自噬活性监测,22:00和2:00在第7节和第10节观察到自噬体;第4节和第13节没有观察到自噬体。在夜间,PeATG1和PeATG4转录水平表达增强,PeATG1表达量在22:00最高,分别是18:00和6:00的3.0倍和1.3倍(P < 0.05);PeATG4表达量在2:00最高,分别是18:00和6:00的1.7和1.6倍(P < 0.05)。 结论 毛竹茎秆不同时间段的生长发育存在显著差异,夜间有自噬体形成,PeATG1和PeATG4基因表达量较高,茎秆生长迅速。 Abstract:Objective The aim is to discuss the relationship between rapid growth of stems of Phyllostachys edulis and gene expression of PeATG1 and PeATG4. Method Stems of P. edulis shoots were used as materials, the autophagic activity at different periods (10:00, 14:00, 18:00, 22:00, 2:00, and 6:00) and in different parts (internodes 4, 7, 10 and 13) was monitored by transmission electron microscope (TEM), and the expression of PeATG1 and PeATG4 genes in the 7th internode was determined by real-time fluorescence quantitative polymerase chain reaction (qRT-PCR). Result The autophagosomes were observed at 22:00 and 2:00 in internodes 7 and 10 during 24 h monitoring, while no autophagosome was observed in internodes 4 or 13. The expression of PeATG1 and PeATG4 enhanced at night. The expression of PeATG1 was highest at 22:00, which was 3.0-fold and 1.3-fold of 18:00 and 6:00 respectively (P < 0.05). The expression of PeATG4 was highest at 2:00, which was 1.7-fold and 1.6-fold of 18:00 and 6:00 respectively (P < 0.05). Conclusion The research showed significant differences in growth and development of P. edulis at different stages. Autophagosomes were formed at night, and the expressions of PeATG1 and PeATG4 were high, which resulted in rapid growth of stems. -
Key words:
- botany /
- Phyllostachys edulis /
- stem /
- autophagy /
- PeATG1 /
- PeATG4 /
- rapid growth
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表 1 本研究所用的引物名称
Table 1. PCR primers used in this study
基因名称 序列 用途 PeATG1-F TTCTACCTCACCCCTACCGA 基因全长扩增 PeATG1-R TTCTTCTTGTTGCGCTCGAG PeATG4-F CTGTCAAGCGTTGTCGTG 基因全长扩增 PeATG4-R AACCAATAGCCAGGGATG PeATG1-F CACCGACATCATCGTCCGCTAC 荧光定量聚合酶链式反应 PeATG1-R TCGCCCTCCCGTGCCTTATC PeATG4-F ATGGCTCTTTATGTTGTTTC 荧光定量聚合酶链式反应 PeATG4-R GTGGGATGTACCTTGGAT PeNTB-F TCTTGTTTGACACCGAAGAGGAG 荧光定量聚合酶链式反应 PeNTB-R AATAGCTGTCCCTGGAGGAGTTT -
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