【作者】 李洁；

【导师】 张吉宇；

【作者基本信息】 兰州大学 ， 作物学·作物栽培学与耕作学， 2020， 硕士

【摘要】 象草（Cenchrus purpureus（Schumach.）Morrone）是一种优质的牧草,具有质地柔嫩、叶量大、营养价值高、适应能力强、再生性好等特点。提高草产量是目前牧草改良的重要目标性状之一,象草的草产量与节间伸长有关。赤霉素（GA₃）是调控植物生长的重要激素,在水稻（Oryza sativa）、油菜（Brassica campestris）、甘蔗（Saccharum officinarum）等植物中均发现赤霉素对节间伸长具有一定的促进作用。本研究对六个象草品种进行了农艺性状的观测,筛选出节间长度及生物量差异最大的桂闽引象草（C.purpureus cv.Gui Min Yin）和矮象草（C.purpureus cv.Mott）;分析了外源GA₃处理对桂闽引象草和矮象草农艺性状和内源激素含量的影响;进一步通过比较转录组分析了象草节间伸长的分子机理。本研究为揭示象草节间伸长机理及草产量分子改良奠定了一定的基础。主要研究结果如下:1.对桂牧一号象草[（C.purpureus cv.Mott）×（C.americanus×C.purpureus）]cv.Guimu No.1、桂闽引象草、紫象草（C.purpureus cv.Red）、矮象草、巨菌草（Pennisetum giganteum z.x.lin暂定名）和王草（C.purpureus×C.americanus cv.Reyan No.4）进行农艺性状（株高、茎粗、节间长度、节间数目、鲜重、干重和茎叶比）的测定和分析,结果表明在六个品种中桂闽引象草的株高、节间长度、鲜重、干重和茎叶比最大,矮象草最小;矮象草的节间数目仅次于桂闽引象草而多于另外四个品种。因此选择节间长度最大、生物量最高的桂闽引象草和节间长度最小、生物量最低的矮象草作为外源GA₃处理的品种。2.分析了外源GA₃处理后桂闽引象草和矮象草农艺性状和内源激素的响应。结果表明外源GA₃处理均显著增加了两者的株高与茎粗（p<0.05）,提前了桂闽引象草首个节间形成的时间;显著增加了桂闽引象草和矮象草内源赤霉素（GA₃）、生长素（IAA）和玉米素核苷（ZR）的含量（p<0.05）,降低了内源脱落酸（ABA）的含量（p<0.05）。总体上,外源GA₃对桂闽引象草各目标性状的促进或抑制作用强于矮象草。3.选取桂闽引象草和矮象草经GA₃处理后0 h、1 h和48 h的茎尖分生组织进行转录组测序分析,筛选得到8859个差异表达基因（DEGs）。GO（Gene Ontology）和KEGG（Kyoto Encyclopedia of Genes and Genomes）富集分析及转录因子预测表明,DEGs主要富集到翻译、氨基酸代谢和碳代谢三个代谢通路;部分DEGs富集到植物对激素的响应和激素信号转导通路,且桂闽引象草包含的基因多于矮象草;同时发现与植物响应赤霉素信号相关的bHLH、MYB、ERF和NAC转录因子家族包含的DEGs较多。加权基因共表达分析（WGCNA）表明,IAA、细胞分裂素（CTK）和油菜素内酯（BR）生物合成及信号转导途径中的一些关键基因（如,AUX/IAA、SAUR、B-ARR、CYP90D2）,可能参与调控桂闽引象草和矮象草的株高与节间伸长过程。实时荧光定量PCR进一步验证了这些基因的表达模式与转录组测序的表达趋势基本一致。更多还原

【Abstract】 Elephant grass（Cenchrus purpureus（Schumach.）Morrone）is a high quality forage with soft texture,abundant leaves,high nutritional value,strong adaptability,and good regenerability.Increasing the grass yield is one of the important target traits of forage improvement,while the yield of elephant grass is related to internode elongation.Gibberellin is an important hormone that regulates plant growth,and was reported to promote internode elongation in rice（Oryza sativa）,rape（Brassica campestris）,sugarcane（Saccharum officinarum）and other plants.In this study,we observed the agronomic traits of six elephant grass cultivars,and then picked out Cp GMY[（C.americanus×C.purpureus）×（C.purpureus cv.Mott）]and Cp Mott（C.purpureus cv.Mott）with the biggest difference between internode length and biomass.Then,we analyzed the effects of exogenous GA₃ treatment on agronomic traits and endogenous hormone content of Cp GMY and Cp Mott.Furthermore,the molecular mechanism of internode elongation was analyzed by comparative transcriptome.This study will provide the foundation for revealing the mechanism of internode elongation in elephant grass and molecular improvement of grass yield.The main results are as follows:1.Determination and analysis of agronomic traits including plant height,stem diameter,internode length,internode number,fresh weight,dry weight,and stem-to-leaf ratio of the six elephant grass cultivars.They were Hybrid Guimu[（C.purpureus cv.Mott）×（C.americanus×C.purpureus）]cv.Guimu No.1,Cp GMY,Cp Red（C.purpureus cv.Red）,Cp Mott,Pg Jujun（Pennisetum giganteum z.x.lin）and King grass（C.purpureus×C.americanus cv.Reyan No.4）.The results showed that the plant height,internode length,fresh weight,dry weight,and stem-to-leaf ratio of Cp GMY were the highest among the six cultivars,while those of Cp Mott were the lowest.The internode number of Cp Mott was more than the other four cultivars,but less than Cp GMY.Therefore,we selected Cp GMY and Cp Mott as the cultivars for exogenous GA₃ treatment.2.We analyzed the response of agronomic traits and endogenous hormone content of Cp GMY and Cp Mott after exogenous GA₃ treatment.The results showed that exogenous GA₃ treatment significantly increased the plant height and stem diameter（p<0.05）,advanced the appearance time of the first internode in Cp GMY;significantly increased the endogenous GA_3,IAA and ZR content and reduced the endogenous ABA content of Cp GMY and Cp Mott（p<0.05）.Generally speaking,the effect of exogenous GA₃ treatment on the promotion or inhibition of target traits in Cp GMY was stronger than those of Cp Mott.3.The shoot apical meristem of 0,1 and 48 h after GA₃ treatment were collected from Cp GMY and Cp Mott,transcriptome sequencing analysis was performed to identify 8859 differentially expressed genes（DEGs）.GO（Gene Ontology）,KEGG（Kyoto Encyclopedia of Genes and Genomes）enrichment analysis and transcription factor prediction showed that genes were mainly enriched in three metabolic pathways of translation,amino acid metabolism and carbon metabolism.Some DEGs were enriched to response to hormone and plant hormone signal transduction pathway,and the number of genes in Cp GMY was more than in Cp Mott.Meanwhile,we found that the bHLH,MYB,ERF and NAC transcription factor families related to plant responsing to gibberellin signal contained more DEGs.The weighted gene co-expression analysis（WGCNA）indicated that some key genes in the biosynthesis and signal transduction pathways of IAA,CTK and BR may be involved in the regulation of plant height and internode elongation of Cp GMY and Cp Mott,such as AUX/IAA、SAUR、B-ARR and CYP90D2.Real-time fluorescence quantitative PCR further verified that the expression of these genes was basically consistent with the transcriptome sequencing.更多还原