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Investigations on the Influence of Cellular Sugar and Endoplasmic Reticulum Dynamics on Plastid Pleomorphy in Arabidopsis Thaliana

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Investigations on the Influence of Cellular Sugar and Endoplasmic Reticulum Dynamics on Plastid Pleomorphy in Arabidopsis Thaliana Investigations on the Influence of Cellular Sugar and Endoplasmic Reticulum Dynamics on Plastid Pleomorphy in Arabidopsis thaliana by Kiah A. Barton A Thesis presented to The University of Guelph In partial fulfilment of requirements for the degree of Doctor of Philosophy in Molecular and Cellular Biology Guelph, Ontario, Canada © Kiah A. Barton, April, 2020 ABSTRACT INVESTIGATIONS ON THE INFLUENCE OF CELLULAR SUGAR AND ENDOPLASMIC RETICULUM DYNAMICS ON PLASTID PLEOMORPHY IN ARABIDOPSIS THALIANA Kiah A. Barton Advisor: University of Guelph, 2020 Dr. Jaideep Mathur Plastids exhibit continuous changes in shape over time, seen either as alterations in the form of the entire plastid or as the extension of thin stroma-filled tubules (stromules). Live-imaging of fluorescently-highlighted organelles was used to assess the role of cellular sugar status and endoplasmic reticulum (ER) rearrangement in this behaviour. Plastids in the pavement cells of Arabidopsis are shown to be chloroplasts and a brief summary of their physical relationship with other cellular structures, their development, and their stromule response to exogenous sucrose is presented. Of the several sugars and sugar alcohols tested, plastid elongation in response to exogenously applied sugars is specific to glucose, sucrose and maltose, indicating that the response is not osmotic in nature. Sugar analogs, used to assess the contribution of sugar signalling to a process, and the sucrose signalling component trehalose-6-phosphate have no effect on stromule formation. Stromule frequency increases in response to multiple nutrient stresses in a sugar- dependent manner. Mutants with increased sugar accumulation show corresponding increases in stromule frequencies, though plastid swelling as a result of excessive starch accumulation negatively affects stromule formation. The elongation and retractions of plastids is seen to correlate with the rearrangement of the ER. Transient dilations in tubular portions of plastids, as iii well as gaps in stromal fluorescence, are associated with regions of spatial interaction with the ER. The degree of plastid elongation correlates with the size of the ER polygons both regionally and at the level of individual plastids, with more elongated etioplasts seen alongside smaller ER polygons. The disruption of ER structure or rearrangement through treatment with Latrunculin B, Brefeldin A or cold temperatures corresponds with a decrease in general plastid elongation and the inhibition of stromule induction by sucrose. The endoplasmic reticulum morphology 1-1 mutant has compromised ER structure and this correlates with a general reduction in plastid tubulation. The evidence presented here suggests that cellular sugar has a pivotal role in inducing plastid pleomorphy in an ER-mediated manner. iv ACKNOWLEDGEMENTS The number of people who have been there to help, support and encourage me throughout this journey seems innumerable. The only conceivable place to begin is by thanking Dr. Jaideep Mathur for encouraging me to think critically, to speak when I have something to say, and to see the beauty as well as the science. You have given me a sense of awe at both the complexity and the majesty of life, fostered a desire to understand it, and encouraged me to appreciate the mystery as much as the answer. My many wonderful co-conspirators in the Mathur Lab were indispensable to both my sanity and my progress throughout. Thank you Ashley, for enabling my addiction to hot chocolate and donuts, and for always being there to chat, to assist, or to escape the lab as necessary; Alena, for your helpfulness and for introducing me to frozen yoghurt; Michael, for being an endless source of scientific know-how and music; Cole, for your optimism and for the fun you brought to the lab; and Kate, for gallivanting across the world with me and being a wonderful friend. I’d also like to thank all of the undergraduate students for their enthusiasm and help, and my ducklings, Jacqueline and Nailah, for their wonderful and hilarious attempts to drag me out into the world. And of course I cannot thank Neeta enough, for being just plain awesome. Neither the plants nor the students would survive without her cheerfulness and care. I would like to thank the members of my advisory committee: Dr. Joseph Colasanti, Dr. Ian Tetlow, and Dr. Barry Shelp, for your encouragement, your constructive criticism, and your thoughtful suggestions. A huge thank you to Bertilla Moroni as well, for being so very kind and helpful. To fellow grad students, thank you for your conversation, commiseration, and words of support. Most especially, thank you Jenelle, for being an awesome roommate and an amazing friend, and for providing me with both encouragement to write and cats to cuddle. My friends and family were with me always. Thank you Mom, for your perpetual willingness to read and edit this thesis, and for never tiring of playing the synonym game when I was struggling to write ‘The Beast’; Dad, for being an endless source of groan-worthy jokes and fun; Grandma and Grand Dad, for your support and encouragement; and Nathan, for providing me with a weekly escape from writing and thus helping me to maintain some pretence of sanity. And a millions thanks to my beloved friends, Andrea, Elizabeth, Meghan, Sheridan, and Bruce, for being your amazing selves. Always there to talk, listen, or create mayhem as required. I apologize that I have not yet managed to create either a tomato that tastes like cake or a dragon made of vegetation, and thank you for supporting me regardless of this oversight. And of course, I would like to acknowledge the Natural Sciences and Engineering Research Council, the Ontario Graduate Scholarship, the Canada Foundation for Innovation, the Dr. Donald R. Phillips Scholarship, and the Molecular and Cellular Biology department of the University of Guelph for providing funding for this research. Last, but definitely not least, I would like to thank the plants for not staging an uprising despite all the things I subjected them to over the years in the interest of science, both standard and mad. v TABLE OF CONTENTS Abstract ........................................................................................................................................... ii Acknowledgements ........................................................................................................................ iv Table of Contents ............................................................................................................................ v List of Tables .................................................................................................................................. ix List of Figures .................................................................................................................................. x List of Abbreviations ..................................................................................................................... xv List of Appendices ........................................................................................................................ xvi 1 General Introduction ................................................................................................................ 1 1.1 Plastids: Types and general characteristics ..................................................................... 1 1.2 Plastid pleomorphy: Stromules, protrusions, and plastid dynamics ................................ 5 1.3 Proposed functions of stromules ..................................................................................... 7 1.4 Potential mechanisms of plastid elongation .................................................................... 9 1.5 Hypotheses .................................................................................................................... 10 2 Pavement cell chloroplasts in Arabidopsis ............................................................................ 11 2.1 Pavement cells in Arabidopsis have chloroplasts .......................................................... 11 2.1.1 Letter to the Editor ................................................................................................. 12 2.2 Chloroplast behaviour and interactions with other organelles in Arabidopsis thaliana pavement cells. .......................................................................................................................... 18 2.2.1 Introduction ........................................................................................................... 18 2.2.2 Results ................................................................................................................... 20 2.2.3 Discussion .............................................................................................................. 37 2.2.4 Methods ................................................................................................................. 42 3 Plastid pleomorphy and cellular sugar status ........................................................................ 45 vi 3.1 Introduction ................................................................................................................... 45 3.2 Results ........................................................................................................................... 51 3.2.1 Confocal imaging of chloroplasts influences plastid behaviour ............................ 51 3.2.2 Short and long-term exogenous sucrose
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