title: Exogenous auxin regulates multi-metabolic network and embryo development, controlling seed secondary dormancy and germination in Nicotiana tabacum L.
abstract: BACKGROUND
  Auxin was recognized as a secondary dormancy phytohormone, controlling seed dormancy and germination. However, the exogenous auxin-controlled seed dormancy and germination remain unclear in physiological process and gene network.
  
  
  RESULTS
  Tobacco seeds soaked in 1000 mg/l auxin solution showed markedly decreased germination compared with that in low concentration of auxin solutions and ddH2O. Using an electron microscope, observations were made on the seeds which did not unfold properly in comparison to those submerged in ddH2O. The radicle traits measured by WinRHIZO, were found to be also weaker than the other treatment groups. Quantified by ELISA, there was no significant difference found in β-1,3glucanase activity and abscisic acid (ABA) content between the seeds imbibed in gradient concentration of auxin solution and those soaked in ddH2O. However, gibberellic acid (GA) and auxin contents were significantly higher at the time of exogenous auxin imbibition and were gradually reduced at germination. RNA sequencing (RNA-seq), revealed that the transcriptome of auxin-responsive dormancy seeds were more similar to that of the imbibed seeds when compared with primary dormancy seeds by principal component analysis. The results of gene differential expression analysis revealed that auxin-controlled seed secondary dormancy was associated with flavonol biosynthetic process, gibberellin metabolic process, adenylyl-sulfate reductase activity, thioredoxin activity, glutamate synthase (NADH) activity and chromatin regulation. In addition, auxin-responsive germination responded to ABA, auxin, jasmonic acid (JA) and salicylic acid (SA) mediated signaling pathway (red, far red and blue light), glutathione and methionine (Met) metabolism.
  
  
  CONCLUSIONS
  In this study, exogenous auxin-mediated seed secondary dormancy is an environmental model that prevents seed germination in an unfavorable condition. Seeds of which could not imbibe normally, and radicles of which also could not develop normally and emerge. To complete the germination, seeds of which would stimulate more GA synthesis to antagonize the stimulation of exogenous auxin. Exogenous auxin regulates multi-metabolic networks controlling seed secondary dormancy and germination, of which the most important thing was that we found the auxin-responsive seed secondary dormancy refers to epigenetic regulation and germination to enhance Met pathway. Therefore, this study uncovers a previously unrecognized transcriptional regulatory networks and physiological development process of seed dormancy and germination with superfluous auxin signal activate.
authors: College of Agriculture and Biotechnology, China Agricultural University, Yuanmingyuan West Road, Beijing, 100094, China. lixing_19841014@126.com.|Molecular Genetics Key Laboratory of China Tobacco, Guizhou Academy of Tobacco Science, GuiYang, 550081, China. lixing_19841014@126.com.
authors: Zhenhua
authors: Z
authors: Li
authors: Molecular Genetics Key Laboratory of China Tobacco, Guizhou Academy of Tobacco Science, GuiYang, 550081, China. zhechen361023@163.com.
authors: Jie
authors: J
authors: Zhang
authors: Institute of Tobacco, Guizhou University, Guiyang, 550025, China. yiyi610@126.com.
authors: Yiling
authors: Y
authors: Liu
authors: Molecular Genetics Key Laboratory of China Tobacco, Guizhou Academy of Tobacco Science, GuiYang, 550081, China. zhaojiehong@126.com.
authors: Jiehong
authors: J
authors: Zhao
authors: Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100081, China. fujunjie@caas.cn.
authors: Junjie
authors: J
authors: Fu
authors: Molecular Genetics Key Laboratory of China Tobacco, Guizhou Academy of Tobacco Science, GuiYang, 550081, China. renxuel@126.com.
authors: Xueliang
authors: X
authors: Ren
authors: Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100081, China. wangguoying@caas.cn.
authors: Guoying
authors: G
authors: Wang
authors: College of Agriculture and Biotechnology, China Agricultural University, Yuanmingyuan West Road, Beijing, 100094, China. wangjh63@cau.edu.cn.
authors: Jianhua
authors: J
authors: Wang
mesh_terms: D000040:Abscisic Acid / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000235:genetics; D007210:Indoleacetic Acids; D053858:Metabolic Networks and Pathways; D057445:Plant Dormancy; D010937:Plant Growth Regulators / Q000502:physiology*; D012639:Seeds / Q000235:genetics / Q000254:growth & development*; D014026:Nicotiana / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D059467:Transcriptome
chemical_list: D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D000040:Abscisic Acid