Clemson University TigerPrints All Dissertations Dissertations December 2017 Towards a Better Understanding of the Molecular Mechanisms Underlying Plant Development and Stress Response Peipei Wu Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Recommended Citation Wu, Peipei, "Towards a Better Understanding of the Molecular Mechanisms Underlying Plant Development and Stress Response" (2017). All Dissertations. 2548. https://tigerprints.clemson.edu/all_dissertations/2548 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. TOWARDS A BETTER UNDERSTANDING OF THE MOLECULAR MECHANISMS UNDERLYING PLANT DEVELOPMENT AND STRESS RESPONSE A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Biochemistry and Molecular Biology by Peipei Wu December 2017 Accepted by: Dr. Hong Luo, Committee Chair Dr. Julia Frugoli Dr. Rajandeep Sekhon Dr. Liangjiang Wang ` ABSTRACT The spectacular array of diverse plant forms as well as the predominantly sessile life style of plants raises two questions that have been fascinating to scientists in the field of plant biology for many years: 1) how do plants develop to a specific size and shape? 2) how do plants respond to environmental stresses given its immobility? Plant organ development to a specific size and shape is controlled by cell proliferation and cell expansion. While the cell proliferation process is extensively studied, the cell expansion process remains largely unknown, and can be affected by several factors, such as cell wall remodeling and the incorporation of new wall materials. To better understand the genetic basis of plant development, we identified an Arabidopsis T-DNA insertion mutant named development related Myb-like 1 (drmy1), which showed altered size and shape in both vegetative and reproductive organs due to defective cell expansion. We further demonstrated that the defective cell expansion in the drmy1 mutant is linked to the change in cell wall composition. Complementation testing by introduction of DRMY1 into the mutant background rescued the phenotype, indicating that DRMY1 is a functional regulator of plant organ development. The DRMY1 protein contains a single Myb-like DNA binding domain and is localized in the nucleus, and may cooperate with other transcription factors to regulate downstream gene expression as DRMY1 itself does not possess transactivation ability. DRMY1 expression analysis revealed that its expression is reduced by the plant hormone ethylene (a negative regulator of cell expansion) while induced by ABA (a positive regulator of cell expansion). Furthermore, whole transcriptome profiling suggested that DRMY1 might control cell expansion directly by regulating genes ii ` related to cell wall biosynthesis/remodeling and ribosome biogenesis or indirectly through regulating genes involved in ethylene and ABA signaling pathways. Plants cannot “escape” from salinity stress but have evolved different mechanisms for salt tolerance over the time of adaptation to salinity. About 1% of plant species named halophytes can survive and thrive in environments containing high salt concentrations, which makes it important to understand their salt tolerance mechanisms and the responsible genes. Here, we investigated salt tolerance mechanisms in Supreme, the most salt-tolerant cultivar of a halophytic warm-seasoned perennial grass, Seashore paspalum (Paspalum vaginatum) at the physiological and transcriptomic levels by comparative study with another cultivar Parish, which possesses moderate salinity tolerance. Our results suggest that Na+ accumulation under normal conditions and further increased accumulation under high salinity conditions (400 mM NaCl), possibly by vacuolar sequestration is a crucial mechanism for salinity tolerance in Supreme. Our data suggests that Na+ accumulation in Supreme under normal conditions might trigger the secondary messenger Ca2+ for signal transduction and the resulting upregulation of salt stress related transcription factors in addition to serving as cheap osmolytes to facilitate water uptake. Moreover, the retention of K+ under salt treatment, which can counteract the toxicity of Na+, is a protective mechanism for both cultivars. A strong oxidation-reduction process and nucleic acid binding activity under high salinity conditions are two other contributors to the salinity tolerance in both cultivars. We also identified ion transporters including NHXs and H+- PPases for Na+ sequestration and K+ uptake transporters, which can be used as candidate iii ` genes for functional studies and potential targets to engineer plants for enhanced salinity tolerance, opening new avenues for future research. iv ` DEDICATION I dedicate this dissertation to my parents, Jinlin Lu and Xiuyun Liu, who give me their best love and support. This work is also dedicated to my husband Yijian Qiu, who helped me get through tough times during my PhD study with encouragement and support. v ` ACKNOWLEDGMENTS Firstly, I would like to express my sincere gratitude to my advisor Dr. Hong Luo for his invaluable guidance and enormous support for my PhD study. I also greatly appreciate my committee members Dr. Julia Frugoli, Dr. Liangjiang Wang, and Dr. Rajandeep Sekhon for their insightful and helpful suggestions on my projects. I would also like to thank my current and previous lab members, Qian Hu, Dr. Zhigang Li, Dr. Ning Yuan and Dr. Zhihui Chang for their generous help and support. I’m also very grateful for the following people: Dr. Steven Cogill (Stanford University), Yijian Qiu (Clemson University), Dr. Christopher Saski (CUGI), Dr. Rooksana Noorai (CUGI), Xiaoxia Xia (CUGI), Dr. Vijay Shankar (CUGI), Wei Li (Clemson University) for their help in RNAseq data analysis; Computing experts Dr. Marcin Ziolkowski, Dr. Linh Ngo, Ashwin Srinath, Jeff Denton from Clemson University Computing and Information Technology (CCIT) for their help in programming and troubleshooting; Dr. Rhonda Reigers Powell from Clemson Light Imaging Facility (CLIF) for her guidance in fluorescence imaging; Dr. Cliff Foster from Michigan State University for his help with cell wall composition analysis; Dr. Cora MacAlister from University of Michigan and Dr. David Jackson from Cold Spring Harbor for providing Lat52B-GUS transgenic Arabidopsis seeds and protocols; Dr. Dayong Li from Chinese Academy of Sciences for providing yeast systems for transactivation assay; Dr. Paul Raymer from University of Georgia for providing Seashore paspalum cultivars. vi ` TABLE OF CONTENTS Page TITLE PAGE .................................................................................................................... i ABSTRACT ..................................................................................................................... ii DEDICATION ................................................................................................................. v ACKNOWLEDGMENTS .............................................................................................. vi LIST OF TABLES ......................................................................................................... ix LIST OF FIGURES ......................................................................................................... x CHAPTER ONE LITERATURE REVIEW AND RESEARCH OBJECTIVES ...................... 1 Part I: The Regulation of Plant Development Cell Proliferation ........................................................................................ 2 Cytoplasmic Growth .................................................................................. 7 Endocycle ................................................................................................... 8 Cell Expansion ......................................................................................... 11 Compensation Mechanism: Organ-Wide Regulation .............................. 15 Part II: The Regulation of Plant Salt Stress Response Na+ Transporters and Plant Salt Tolerance .............................................. 18 Compatible Solutes and Osmotic Adjustment ......................................... 21 Antioxidative Defense Mechanism .......................................................... 22 Salt Signaling and Regulatory Pathways ................................................. 22 Salt Tolerance Mechanisms in Halophytes .............................................. 28 Part III: The Objectives of the Current Research ..................................... 30 TWO DRMY1, A NOVEL MYB-LIKE TRANSCRIPTION FACTOR REGULATES CELL EXPANSION DURING PLANT DEVELOPMENT AND AFFECTS SEED PRODUCTION IN ARABIDOPSIS ............................................................................... 31 Abstract .................................................................................................... 32 Introduction .............................................................................................. 32 Methods.................................................................................................... 37 vii ` Results ...................................................................................................... 45 Discussion ...............................................................................................