Thesis Submitted for the Degree of Doctor of Philosophy
Total Page:16
File Type:pdf, Size:1020Kb
University of Bath PHD Phytochemistry of hydroxycoumarins from Manihot esculenta Euphorbiaceae (cassava) Alhalaseh, Lidia Award date: 2017 Awarding institution: University of Bath Link to publication Alternative formats If you require this document in an alternative format, please contact: [email protected] General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 07. Oct. 2021 Phytochemistry of hydroxycoumarins from Manihot esculenta Euphorbiaceae (Cassava) Lidia Kamal Jameel Alhalaseh A thesis submitted for the degree of Doctor of Philosophy University of Bath Department of Pharmacy and Pharmacology August 2017 COPYRIGHT Attention is drawn to the fact that copyright of this thesis rests with its author. A copy of this thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and they must not copy it or use material from it except as permitted by law or with the consent of the author. This thesis may be made available for consultation within the University Library and may be photocopied or lent to other libraries for the purposes of consultation. Signed on behalf of the Faculty of Science. Signed: ……………………………… Date: …………………….. 1 Abstract This is an interdisciplinary research project on cassava (Manihot esculenta Crantz, Euphorbiaceae) ultimately working towards producing cassava roots which are long-lasting, free of post-harvest physiological deterioration (PPD). It aims to contribute to ensuring food security. In cassava, scopoletin and its -glycoside scopolin are considered phytoanticipants, not phytoalexins, due to their increasing accumulation during the PPD process compared to their barely detectable levels in fresh roots. Starting with a focussed literature review on the potential of cassava, contrasted with its limitations on harvesting due to PPD, and biosynthesis along the phenylpropanoid pathway of key hydroxycoumarins, e.g. scopoletin and esculetin, the associated gaps in our current knowledge have been set out. Whether scopoletin is biosynthesized de novo from L-phenylalanine in response to stress, or whether stress prompts its release from the corresponding glycoside is unknown. Therefore, assessing hydroxycoumarin biosynthesis and quantifying their accumulation patterns have been undertaken in wild-type and transgenic plants in order to elucidate the divergence in scopoletin biosynthetic pathways. The identification of key genes on each pathway leading to scopoletin in cassava, and then exploring their functional identities using the model plant A. thaliana and genetically engineered E. coli, where the genes were isolated, cloned, and expressed, were also undertaken. Transgenic A. thaliana lines with no activity of the key enzymes on the proposed pathway, namely F6ʹH1, CCoAOMT, and EOMT, were developed. Competition feeding experiments using stable isotopically labelled potential biosynthetic intermediates showed the incorporation of labelled ferulate into scopoletin in transgenic A.t-F6´H1 and M.e-F6´H. This confirmed the activity of other hydroxylase enzymes rather than F6´H1 in the ortho-hydroxylation steps. The hydroxycoumarins of interest were isolated, characterized, and quantified in the wild type and mutant lines using chromatographic and spectroscopic techniques, mainly NMR, HR-MS, and LC- MS. Taken together, a significant contribution to knowledge about hydroxycoumarin biosynthesis has been made. 2 This Thesis is dedicated to my late father 3 Acknowledgements I express my deepest gratitude to my main supervisor Dr Ian S. Blagbrough for giving me the chance to explore freely during the 3-labworking years, and for his tireless efforts in proofreading my dissertation during writing-up. Also, for his guidance, persistent assistance, and support especially in family-related issues. I also thank my co-supervisors Dr John R. Beeching and Dr Michael G. Rowan without their valuable constructive suggestions, constant support and guidance over the course of my PhD the completion of this project would not have been achievable. Dr Shaun B. Reeksting has my gratefulness for his assistance with the LC- MS spectroscopic experiments, and for being patient and welcoming despite my fussy comments and endless repetitive analysis. I thank Dr Tim J. Woodman for his assistance with the NMR spectroscopic experiments. Thank you also to Don Perry, Andrew James, and all the technical staff in the Department of Pharmacy and Pharmacology and the Department of Biology and Biochemistry, University of Bath, for helping me to overcome many technical issues. I gratefully thank Mu´tah University, Jordan for granting me this PhD scholarship. Very special thanks to my colleagues in 5W3.20 and 4S1.52 for the friendly working environment and for all the useful scientific discussions we had which contributed considerably to this project. A special thanks to Dr Soad A. Bayoumi and Dr Shi Liu whose previous work got me inspired in cassava. Finally, my deepest thanks to my parents, parents in law, sisters and brother who were always encouraging and supportive. My greatest thanks go to my husband Dr Mohannad J. Al-Zregat for showing faith in me, for his selfless love, and for his moral and financial support. Words will never be enough to express how grateful I am to my daughters Diana and Katia for having the magical tools to draw a smile on my face even in the most difficult and stressful moments I have ever experienced. 4 Abbreviations µg microgram 4CL 4-coumarate CoA ligase 4-MU 4-methylumbelliferone ACMV African Cassava Mosaic Virus aq. aqueous att attachment site bp base pair C3´H p-coumaroyl shikimate/quinate 3´-hydroxylase C4´H cinnamate-4´-hydroxylase CAMBIA Centre for the Application of Molecular Biology to International Agriculture CBM cassava basic medium CCoAOMT caffeoyl CoA 3´-O-methyltransferase cDNA complementary DNA COMT caffeic acid methyltransferase CTAB cetyl trimethyl ammonium bromide Da Dalton DMSO dimethylsulfoxide DNA deoxyribonucleic acid EDTA ethylene diamine tetra acetic acid ESI electrospray ionization F6´H feruloyl CoA 6´-hydroxylase Fw forward GMO genetically modified organisms GST glutathione-S-transferase GT glucosyltransferase GUS β-glucuronidase gene h hour HCT shikimate: quinate hydroxycinnamoyl transferase HPLC high performance liquid chromatography HRMS high resolution mass spectrometry 5 HSQC heteronuclear single quantum coherence Hz Hertz IAA iso-amyl alcohol LB Luria-Bertani medium LB1 left border primer LC-MS liquid chromatography-mass spectrometry LLD lower limit of detection LLQ lower limit of quantification LP left primer M molar m/z mass over charge MCS multiple cloning sites MES 2-(N-morpholino)ethane-sulfonic acid mg milligram MHz mega-Hertz ml millilitre MS mass spectrometry NASC Nottingham Arabidopsis Stock Centre NCBI the National Centre for Biotechnology Information ng nanogram NMR nuclear magnetic resonance ºC degree Celsius OD optical density OMT O-methyl transferase PAL phenylalanine ammonia lyase PCR polymerase chain reaction PPD post-harvest physiological deterioration ppm parts per million PVP poly vinyl pyrrolidone RCF relative centrifugal force RE restriction enzyme Rev reverse Rf retention factor 6 RH relative humidity RNA ribonucleic acid RNAi RNA interference RNase ribonuclease ROS reactive oxygen species RP right primer RT reverse transcriptase SAM S-adenosyl-L-methionine SDS sodium dodecyl sulfate SOC super optimal broth with catabolite repression SOD superoxide dismutase SPE solid phase extraction TAE tris-acetate EDTA TIGER The Institute for Genome Research TLC thin layer chromatography Tris tris(hydroxymethyl)methylamine UDP-glucose uridine diphosphate-glucose UTR untranslated region v/v volume/volume w/v weight/volume w/w weight/weight X-Gal 5-bromo-4-chloro-3-indoyl-β-D-galactoside 7 Contents Abstract 2 Dedication 3 Acknowledgements 4 Abbreviations 5 Chapter 1. General introduction and literature review 10 1.1. Aims and objectives 10 1.2. Cassava 12 1.3. Phenylpropanoids 21 Chapter 2. The roles of hydroxycoumarins in M. esculenta and A. thaliana under normal and abiotic stress conditions 32 2.1. Introduction 32 2.2. Materials 34 2.3. General methods 36 2.4. Results and discussion 41 Chapter 3. Complementation of Arabidopsis thaliana mutants through expressing cassava O-methyltransferase genes 58 3.1. Introduction 58 3.2. Materials 61 3.3. General methods 67 3.4. Results and discussion 84 Chapter 4. Tracing scopoletin biosynthesis in wild type and transgenic M. esculenta and A. thaliana 100 4.1. Introduction 100 4.2. Materials 103 4.3. General methods 103 4.4. Results and discussion 108 8 Chapter 5. Functional expression of cassava O-methyltransferase enzymes in transgenic Escherichia coli 150 5.1. Introduction 150 5.2. Materials 154 5.3. General methods