A Simple Metabolic Switch May Activate Apomixis in <I>Arabidopsis
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Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 12-2018 A Simple Metabolic Switch May Activate Apomixis in Arabidopsis thaliana David Alan Sherwood Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Agronomy and Crop Sciences Commons, and the Molecular Biology Commons Recommended Citation Sherwood, David Alan, "A Simple Metabolic Switch May Activate Apomixis in Arabidopsis thaliana" (2018). All Graduate Theses and Dissertations. 7409. https://digitalcommons.usu.edu/etd/7409 This Dissertation is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. A SIMPLE METABOLIC SWITCH MAY ACTIVATE APOMIXIS IN ARABIDOPSIS THALIANA by David Alan Sherwood A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Plant Science – Molecular Biology Approved: _________________________ _________________________ John G. Carman Ph.D. Bruce Bugbee Ph.D. Major Professor Committee Member _________________________ _________________________ Lee Rickords Ph.D. Steve Larson Ph.D. Committee Member Committee Member _________________________ __________________________ Zhongde Wang Ph.D. Laurens H. Smith Ph.D. Committee Member Interim Vice President for Research and Dean of the School of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2018 ii COPYRIGHT © David Sherwood 2018 All Rights Reserved iii ABSTRACT A Simple Metabolic Switch May Activate Apomixis in Arabidopsis thaliana by David Alan Sherwood, Doctor of Philosophy Utah State University, 2018 Major Professor: Dr. John G. Carman Department: Plants, Soils and Climate Apomixis, asexual or clonal seed production in plants, can decrease the cost of producing hybrid seed and enable currently open pollinated crops to be converted to more vigorous and higher yielding hybrids. Apomixis can also accelerate plant breeding programs by enabling the selection and perpetuation of individuals with unique genetic combinations rather than using uniform inbreds. Facultative apomictic plants can switch between sexual and apomictic reproduction based on stress signaling. RNAseq studies identified differentially expressed genes and enriched GO categories suggesting that a stress-induced down regulation of growth phase genes may be responsible for the shift from apomictic to sexual reproduction. The initiation of stress signaling during female meiosis (megasporogenesis) was analyzed in the wildtype obligately sexual Arabidopsis thaliana by the co-analysis of meiocyte callose accumulation and chromosome condensation. The onset of callose accumulation generally occurred within 3 hours after the lights came on in the morning and coincided with pachytene, the 3rd step of meiotic prophase I that generally fails in apomictic plants. Topical application of glucose or brassinosteroids, within the correct developmental window, was used to halt stress iv signaling and shift metabolism to a pro-growth status. This triggered high rates of 1st division meiotic restitution, reminiscent of Taraxicum type diplospory that lacked callose. Dyads of unreduced megaspores then formed, and the chalazal most cell of the dyad in these ovules produced an unreduced eight nucleate polygonum type embryo sac. A similar topical application of glucose and brassinosteroids near the end of embryosac maturation (8 nucleate stage prior to the fusion of the two central cells) was necessary to trigger parthenogenesis in either haploid or unreduced (diploid) ovules. These results suggest that fully functional apomixis might be achieved in wild-type obligately sexual Arabidopsis thaliana by shifting metabolic signals within appropriate developmental windows. This discovery also suggests that apomixis is not a mutationally derived condition caused by ‘broken genes’, but rather an alternative mode of reproduction anciently imbedded in the genomes of angiosperms that can be triggered by the appropriate metabolic signals. v PUBLIC ABSTRACT A Simple Metabolic Switch May Activate Apomixis in Arabidopsis thaliana David Alan Sherwood Apomixis, asexual or clonal seed production in plants, can decrease the cost of producing hybrid seed and enable currently open pollinated crops to be converted to more vigorous and higher yielding hybrids that can reproduce themselves through their own seed. Sexual reproduction may be triggered by a programmed stress signaling event that occurs in both the meiocyte, just prior to meiosis, and later in the egg just prior to embryo sac maturation. The prevention of stress signaling and the activation of a pro- growth signal prior to meiosis triggered apomeiosis, the first half of apomixis. The same approach was used prior to embryo sac maturation to trigger parthenogenesis, the second half of apomixis. This discovery suggests that apomixis exists as a program that can be activated by the appropriate metabolic signal at the appropriate developmental stages. Therefore, apomixis may be alternative mode of reproduction rather a ‘broken’ form of sexual reproduction. vi ACKNOWLEDGMENTS I would like to pour my heart out in gratitude to my dedicated wife who has sacrificed much of her time with me in raising 3 active boys while school and research consumed most of my daily thoughts, time and energy. We won’t get those years back but we do cherish our days together as they will continue to come one by one for the rest of eternity. A very special thanks to my adviser, Dr. John Carman, who has guided me through my graduate learning process and has engaged me in endless discussions that have bettered my critical thinking. I would like to thank my committee members for their support and contribution, Dr. Bruce Bugbee, Dr. Lee Rickords, Dr. Steve Larson and Dr. Zhongde Wang. David Alan Sherwood vii CONTENTS Page ABSTRACT ...................................................................................................................... iii PUBLIC ASTRACT ...........................................................................................................v ACKNOWLEDGEMENTS .............................................................................................. vi CONTENTS ..................................................................................................................... vii LIST OF TABLES ............................................................................................................ ix LIST OF FIGURES ............................................................................................................x CHAPTER I. INTRODUCTION ......................................................................................................1 LITERATURE CITED ..........................................................................................16 II. STRESS INDUCED SEXUAL REPRODUCTION IN APOMICTIC BOECHERA WAS CORRELATED WITH DOWN-REGULATION OF GROWTH PHASE GENES ...............................................................................25 ABSTRACT ...........................................................................................................25 INTRODUCTION .................................................................................................27 MATERIALS AND METHODS ...........................................................................28 RESULTS AND DISCUSSION ............................................................................30 LITERATURE CITED ..........................................................................................43 III. METABOLICALLY SWITCHING MEIOSIS INTO APOMEIOSIS ....................45 ABSTRACT ...........................................................................................................45 INTRODUCTION .................................................................................................46 MATERIALS AND METHODS ...........................................................................49 RESULTS AND DISCUSSION ............................................................................53 LITERATURE CITED ..........................................................................................68 IV. PROGRAMMING THE EGG FOR PARTHENOGENESIS AND TRIGGERING AUTONMOUS ENDOSPERM FORMATION .............................77 ABSTRACT ...........................................................................................................77 INTRODUCTION .................................................................................................78 MATERIALS AND METHODS ...........................................................................79 viii RESULTS AND DISCUSSION ............................................................................81 LITERATURE CITED ..........................................................................................87 V. SUMMARY ..............................................................................................................89 LITERATURE CITED ..........................................................................................91 VI. CURRICULUM VITAE ..........................................................................................92 ix LIST OF TABLES Table Page 2.1 Differentially expressed genes across species (control growth conditions) ...............31 2.2 Differentially expressed genes