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薄壳山核桃Carya illinoensis又称长山核桃、美国山核桃,为世界著名的高档干果、油料树种和材果兼用优良树种,其果实营养丰富,保健价值高[1]。研究发现:长期食用薄壳山核桃有明显的防衰老、健肠胃、防治心血管疾病等作用[2]。然而,薄壳山核桃树体高大,不利于人工采摘果实及日常的养护管理,培育矮化砧木可为薄壳山核桃育种工作及果品的推广提供便利。魏灵珠等[3]提出:赤霉素 (gibberellins,GA3) 是调控植物株高的重要激素,相关株高基因的克隆与分子机制研究对于合理调控植物生长发育和农业生产具有极其重要的利用价值。赤霉素作为一类二萜类植物激素,调节种子萌发[4−5]、茎杆伸长[6]、花粉管生长[7]、花和种子发育[8]等多种生理活动,也能在环境胁迫下调控植物的生长和发育[9]。其中,值得关注的是赤霉素通过促进节间伸长来调控植株的营养生长[10]。目前,已经克隆到赤霉素生物合成大多数步骤催化酶的基因,构建了从前体分子到活性赤霉素的整体合成框架[11]。研究发现:赤霉素后期的代谢酶(GA20ox、GA3ox、GA2ox)对活性赤霉素的精确调控具有关键作用[12]。GA20氧化酶(GA20-oxidase, GA20ox)是赤霉素合成过程中关键的限速酶,在棉花Gossypium spp.[13]、毛白杨Populus tomentosa[14]和山茶Camellia reticulata[15]中过表达会使得植株增高,抑制该基因在烟草Nicotiana tabacum[16]、苹果Malus domestica[17]等植株中表达则会使植株矮化。邓伟等[14]通过农杆菌介导法在毛白杨中过量表达棉花GA20ox使得杨树的茎伸长,但减少了叶片和根的生长。赵恺[17]通过农杆菌介导法将GA20ox的干扰信号转入苹果中,获得了苹果的矮化砧木。GA3氧化酶(GA3-oxidase, GA3ox)则是赤霉素合成过程中的一个关键酶。研究发现:抑制小麦Triticum aestivum[18]和水稻Oryza sativa[19]中的GA3ox基因表达,植株会呈现矮化的性状。刘颖等[18]发现:在矮杆小麦‘宁98-2105’中,GA3ox1和GA3ox2在茎的倒一节结节中的转录水平显著高于对照,推测是赤霉素传导通路受到影响导致植株突变。而过量表达赤霉素合成过程中的另一个关键酶赤霉素氧化酶(GA2-oxidase, GA2ox),也会使麻疯树Jatropha curcas[20]、荔波连蕊茶Camellia lipoensis[21]和矮牵牛Petunia hybrida[22]等植株矮化。HU等[20]运用农杆菌介导法在麻疯树中过表达JcGA2ox发现:植株呈现矮化,更小更深的叶片,花序果实都变小的性状。本研究以薄壳山核桃幼苗为实验材料,于生长期喷施100 mg·L−1的赤霉素,研究其对薄壳山核桃幼苗生长的影响和赤霉素合成代谢关键基因的时空变化,初步了解薄壳山核桃GA20ox、GA3ox和GA2ox基因的时空表达特征及在赤霉素合成中的调控作用,为薄壳山核桃矮化新种质育种奠定基础。
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实验薄壳山核桃种子是半同胞家系,2018年10月采摘于浙江农林大学同一株树,挑选大小一致的种子作为实验材料。晾晒后置于塑封袋内,置于4 ℃保存。2019年4月,将薄壳山核桃种子种在基质土[m(泥炭)∶m(珍珠岩)∶m(蛭石)=1∶1∶1]内,在亚热带森林培育国家重点实验室的驯化室[(25±2) ℃,湿度为75%]进行萌发培养。2019年5月,选取生长势、株高、节间长度和主根长度等形态指标基本一致的幼苗54株,叶面喷施100 mg·L−1的赤霉素(CAS: 77-06-5, BC, 上海生工)进行处理(24 h内不浇水),以去离子水为对照,3次重复。
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处理28 d 后测量植株高度、顶芽至第1叶节间长度和主根长度,均用直尺测量,保留1位小数。采用SPSS 17.0中的单因素方差分析对所有指标进行统计处理,P<0.05为差异显著,P<0.01为差异极显著。
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薄壳山核桃、山核桃Carya cathayensis和核桃Juglans regia 的GA20ox、GA3ox和GA2ox均由浙江农林大学省部共建亚热带森林培育国家重点实验室张启香课题组克隆。从美国国家生物信息中心(NCBI)(http://www.ncbi.nlm.nih.gov/)上分别搜索已报道的植物 GA20ox、GA3ox、GA2ox 同源基因的氨基酸序列,通过软件DNAMAN进行氨基酸序列比对。利用ITOL (https://itol.embl.de/)和MEGA制作系统进化树。
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对处理 0、7、14、21和28 d后植株的叶片进行采样,用于基因不同时间表达变化;基因不同空间表达变化采用处理0和28 d后植株的顶芽、叶①、茎①、叶②、茎②、叶③、茎③、叶④、茎⑤和根(图1)。样品采集后立即放入液氮,总RNA的提取方法按照RNAprep pure Plant Kit(北京天根)及其说明书提供的方法进行。用Prime ScriptTM RT Master Mix (TaKaRa公司)反转录合成cDNA。
根据基因序列,利用Primer3Input(http://primer3.ut.ee/)设计定量引物,以山核桃Actin基因为内参,引物序列见表1。荧光定量PCR反应体系为10.0 μL,包含cDNA 0.4 μL,TBGREEN (TaKaRa公司)5.0 μL,正向引物0.2 μL,反向引物0.2 μL,双蒸水 4.2 μL。反应条件为:95 ℃ 10 min;95 ℃ 10 s,60 ℃ 31 s,40个循环;95 ℃ 15 s,60 ℃ 1 min,95 ℃ 30 s,60 ℃ 15 s。数据分析采用7300system软件和2−∆∆Ct的方法,ΔΔCt = (Ct靶基因−Ct内参)处理组−(Ct靶基因− Ct内参)对照组[23-24]。图表由 Excel 2007 软件制作。
表 1 引物序列
Table 1. Primers sequences
引物名称 上游引物(5′→3′) 下游引物 (5′→3′) RTCiGA20ox GCACACCGACCCACAAATCATT TGAGTTCTGATCAGGTGGGACT RTCiGA3ox CACTCGAACAATTCCGCCAACT TGCCCAAGGAGCCTAGCATTAG RTCiGA2ox CAGGTAGGTGGGCTTCAAGTGT CCCGATGCAAGCAACTTTTGTA CcActin TGCGGGTGCTCGCTTCGGCAGC GGGCAGCCAAGGATGACT
Effects of exogenous gibberellin on growth of Carya illinoensis and its metabolic gene expression
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摘要:
目的 研究赤霉素(gibberellin)对植物株高的影响,探讨了GA20ox、GA3ox和GA2ox在赤霉素合成过程中的反馈调节机制。 方法 以薄壳山核桃Carya illinoensis幼苗为材料,进行100 mg·L−1 赤霉素叶面喷施处理。对外施赤霉素后薄壳山核桃的株高、节间长度和主根长以及薄壳山核桃GA20ox、GA3ox和GA2ox的时空变化进行了研究。 结果 外施赤霉素28 d后,薄壳山核桃节间长度和主根长的伸长量与对照相比都存在显著差异(P<0.05),节间数量没有发生变化;植株平均生长量达2.9 cm,为对照的1.93倍,差异极显著(P<0.01)。实时荧光定量PCR结果表明:GA20ox、GA3ox和GA2ox在薄壳山核桃生长期存在时空表达差异。外施赤霉素能够使CiGA20ox的表达量持续下降,28 d后的表达量仅为初始值的38.6%;而CiGA3ox表达量则是在7 d时跌落低谷,下降至初始值的55.4%,28 d后回升,表达量为初始值的350%;CiGA2ox表达量总体呈波浪形变化,在7 d后达到顶峰,之后有所回落,至21 d时恢复到了初始水平,28 d后上升为初始值的220%。CiGA3ox在薄壳山核桃植株茎杆内发生了累积,相较于CiGA20ox和CiGA2ox在转录水平上发生了较大的变化。 结论 外施赤霉素促进了薄壳山核桃茎杆伸长,同时引起了薄壳山核桃体内赤霉素代谢关键基因表达模式的时空变化。图6表1参29 Abstract:Objective This study attempts to explore the effect of gibberellin(GA3) on plant height and discuss the feedback regulation mechanism of GA20ox, GA3ox and GA2ox in the process of GA3 synthesis. Method The leaves of Carya illinoensis seedlings were sprayed with 100 mg·L−1 GA3. The plant height, internode length and main root length of C. illinoensis and the spatiotemporal variation of CiGA20ox, CiGA3ox and CiGA2ox were studied. Result After 28 days of GA3 application, the internode length and the elongation of the main root length of C. illinoensis seedlings were significantly different from those of the control(P<0.05), but the number of internodes did not change. The average plant growth was 2.9 cm, which was 1.93 times that of the control, and the difference was extremely significant (P<0.01). The results of real-time PCR showed that there were spatial-temporal differences in the expression of GA20ox, GA3ox and GA2ox during the growth period of C. illinoensis. Exogenous GA3 could continuously reduce the expression of CiGA20ox. After 28 days, the expression level of CiGA20ox was only 38.6% of the initial value. The expression level of CiGA3ox dropped to a low point of 55.4% of the initial value on day 7 and rose to 350% of the initial value on day 28. The expression level of CiGA2ox in general showed a wavy change, reaching the peak after 7 days, then falling back to the initial level after 21 days, and rising to 220% of the initial value after 28 days. However, CiGA3ox accumulated in the stem of C. illinoensis seedlings, which changed in transcription level compared with CiGA20ox and CiGA2ox. Conclusion The exogenous GA3 could promote the stem elongation of C. illinoensis and cause the temporal and spatial variation of the key gene expression patterns of GA3 metabolism in C. illinoensis. [Ch, 6 fig. 1 tab. 29 ref.] -
表 1 引物序列
Table 1. Primers sequences
引物名称 上游引物(5′→3′) 下游引物 (5′→3′) RTCiGA20ox GCACACCGACCCACAAATCATT TGAGTTCTGATCAGGTGGGACT RTCiGA3ox CACTCGAACAATTCCGCCAACT TGCCCAAGGAGCCTAGCATTAG RTCiGA2ox CAGGTAGGTGGGCTTCAAGTGT CCCGATGCAAGCAACTTTTGTA CcActin TGCGGGTGCTCGCTTCGGCAGC GGGCAGCCAAGGATGACT -
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.20190566