Role of Fatty Acid Omega-Hydroxylase 1 and Abscisic Acid in Potato Tuber Suberin Formation
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Western University Scholarship@Western Electronic Thesis and Dissertation Repository 5-18-2016 12:00 AM Role of Fatty Acid omega-Hydroxylase 1 and Abscisic Acid in Potato Tuber Suberin Formation Meg Haggitt The University of Western Ontario Supervisor Dr. Mark Bernards The University of Western Ontario Graduate Program in Biology A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Meg Haggitt 2016 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Plant Biology Commons Recommended Citation Haggitt, Meg, "Role of Fatty Acid omega-Hydroxylase 1 and Abscisic Acid in Potato Tuber Suberin Formation" (2016). Electronic Thesis and Dissertation Repository. 4074. https://ir.lib.uwo.ca/etd/4074 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Role of Fatty Acid omega-Hydroxylase 1 (FAωH1) and Abscisic Acid in Potato Tuber Suberin Formation Thesis format: Integrated-Article By Meghan L. Haggitt Department of Biology, Faculty of Science A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy SCHOOL OF GRADUATE AND POSTDOCTORAL STUDIES THE UNIVERSITY OF WESTERN ONTARIO LONDON, ONTARIO, CANADA © Meghan L. Haggitt 2016 Abstract Suberin is a complex biopolymer composed of two distinct but covalently-linked domains. The first domain is composed of polymerized phenolic monomers, whereas the second domain is predominately fatty acid derivatives esterified with glycerol. Deposited in specialized cells during development or in response to abiotic stress, suberin functions as a barrier against water loss and pathogen attack. In potato, more than 65% of suberin monomers undergo ω-hydroxylation, representing a major class of fatty acids in the final biopolymer. The ω-hydroxylation reaction is catalyzed by Cytochrome P450 (CYP) proteins, of which few have been characterized to date. In 2009, CYP86A33 from potato was identified and implicated as the main suberin-associated ω-hydroxylase by another research group through RNAi gene silencing; although functional characterization of in vitro protein was unsuccessful. Simultaneously, I identified and characterized gene expression patterns for three CYP86A and CYP94A ω-hydroxylase genes in potato. From this expression analysis, I identified CYP86A33 as the primary candidate for a suberin- associated ω-hydroxylase, from which ω-hydroxylase activity was confirmed through an in vitro enzyme assay with recombinant protein. Following an in silico analysis of the CYP86A33 promoter region, which identified many ABA-responsive promoter elements, an extensive analysis of the effects of ABA on gene expression and suberin biosynthetic regulation was conducted. Using a biosynthetic inhibitor of ABA production, fluridone, I investigated the effects of ABA on suberin regulation by inhibiting ABA de novo biosynthesis with or without the addition of exogenous ABA. Using wounded potato tubers, three parallel timecourse experiments were conducted with different treatments to quantify the ABA concentration, suberin-associated gene expression, and soluble and i insoluble aliphatic monomer deposition into the suberin biopolymer. Expression of suberin-associated genes, including CYP86A33, was reduced post-wounding with fluridone treatment. Similarly, insoluble aliphatic monomer accumulation was nearly eliminated from suberin in fluridone-treated tissues, exhibiting both chain length and monomer class specific effects. These fluridone effects on gene expression and suberin deposition were rescued through the addition of exogenous ABA. Overall, ABA was shown to have a regulatory post-wounding effect on the gene expression of key suberin- associated genes, with concomitant downstream impact on aliphatic suberin deposition. Key words: Solanum tuberosum, potato, suberin, CYP86A33, FAωH1, ω-hydroxylation, abscisic acid, fluridone, wounding ii Statement of Co-Authorship The following people contributed to the publication of the work undertaken as part of this thesis: University of Western Ontario, London, Canada: Meghan L. Haggitt University of Western Ontario, London, Canada: Anica Bjelica Author details and their roles: Bjelica A, Haggitt ML, Woolfson KN, Lee DNP, Makhzoum AB, Bernards MA. 2016. Fatty Acid ω-Hydroxylases from Solanum tuberosum. Accepted pending revisions to Plant Cell Reports Located in Chapter 2, discussed in Chapter 4 Candidate was the secondary author, who identified CYP86A33, cloned CYP86A33 and its promoter, created promoter deletion construct library (12 constructs), and conducted semi-quantitative RT-PCR tissue-specific expression analysis. AB completed all complementation assays, including aliphatic suberin analysis, and promoter analyses. KNW conducted qPCR to repeat tissue-specific expression for publication. DNPL created the CYP86A33 minimal promoter construct for the P2 allele. ABM established hairy root cultures in the lab group. MAB supervised the lab work and wrote the manuscript. Haggitt ML, Woolfson KN, Zhang Y, Kachura A, Bjelica A, Bernards MA. Differential Regulation of Polar and Non-Polar Metabolism During Wound-Induced Suberization in Potato (Solanum tuberosum) tubers. In preparation for submission to The Plant Cell Located in Chapter 3, discussed in Chapter 4 Candidate was the first author, who co-designed and conducted ABA and FD treatments on wound-healing potato tissue, isolated the wounded tissue, conducted semi-quantitative RT-PCR and non-polar metabolite analysis. KNW conducted qPCR to repeat tissue-specific expression for publication. YZ conducted the parallel ABA quantification in treated potato tissued. AK repeated the ABA and FD experiment and prepared the polar metabolites for analysis. AB conducted the polar metabolite analysis. MAB evaluated the polar metabolites, supervised the lab work and wrote the manuscript. iii Acknowledgements Firstly, I extend my sincere and utmost gratitude to my supervisor, Dr. Mark Bernards. Your guidance and leadership throughout my Ph.D study created a truly enjoyable environment to work in, and I learned a great deal that far exceeded my field of study. In addition, I thank my advisory committee, Dr. Denis Maxwell and Dr. Chris Guglielmo. You have both impacted my development as a researcher and provided guidance throughout my degree, for which I am truly grateful. Special thanks to Dr. Maxwell for acting as a reader for my thesis, your thoughtful insights were appreciated. Besides my formal advisors, there were so many other professors who provided guidance throughout my time at Western, including but not limited to Dr. Kathleen Hill, Dr. Susanne Kolhami, Dr. Norm Huner, Dr. Yolanda Morbey, Dr. Sheila Macfie and Dr. Charlie Trick. Thank you for your generosity with your time, it will be remembered. I also thank my fellow lab mates over the years whom I have had the pleasure of working with, in particular Andrea Neculai, Dr. Dimitre Ivanov, Anica Bjelica, Dr. Yanni Zhang, Dr. Leon Kurepin and Trish Tully. Many hours we spent pondering the world while we worked at our lab benches, and I truly enjoyed the lively and diverse discussions. Also, thank you to all the past and present fellow graduate students on 4th floor NCB and beyond. Thank you for the stimulating and often unpredictable discussions. I will remember the many grad club lunches and laughs we had over the years. iv I am very grateful to my parents, Lois and Glenn Hayter, for their incredible support and guidance. As I have grown up I have realized the incredible gifts you gave me, including the solid belief I could achieve whatever I put my mind to and the knowledge that you will always be there to encourage and support me every step of the way. I have not always chosen the conventional path, but you never doubted that I would get there in my own time. I love you both and I am grateful to have you in my life. Words cannot express the extraordinary gratitude I have for my incredible partner in life, Dave Haggitt. So often I am asked how I balance it all in my life, and the answer is being partnered with you. I have never met another person who approaches the world with such a kindness, generosity and true appreciation for how to fully support others in their goals. Saying that I am lucky to have chosen you as my partner in life is an understatement and, with having spent more than half our lives together already, I can’t imagine it any other way. As you have been right alongside me through my entire education, I feel this achievement belongs in part to you. You handled the many, many nights of solo childcare with amazing grace, and I am so thankful for your love and leadership in our family. Last but definitely not least, my two beautiful little ladies, Taya and Lexi. As you grow up I know you too will have the chance to build a life you love to live, find incredible people to surround yourself from which to learn, and choose follow your passions. I hope I can infuse in you a love of learning as great as mine, so that you may find your own amazing opportunities to explore the world. v Table of Contents Abstract ................................................................................................................................ i Statement of Co-Authorship ..........................................................................................