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Effects of Gibberellin 2-Oxidase, Phytochrome B1, and Bas1

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EFFECTS OF GIBBERELLIN 2-OXIDASE, PHYTOCHROME B1, AND BAS1 GENE TRANSFORMATION ON CREEPING BENTGRASS PHOTOMORPHOGENESIS UNDER VARIOUS LIGHT CONDITIONS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jia Yan, M.S. ***** The Ohio State University 2007 Dissertation Committee: Approved by Dr. Karl Danneberger, Advisor Dr. David Gardner Dr. Lisa Lee Dr. Jim Metzger Advisor Graduate Program in Dr. Guo-liang Wang Horticulture and Crop Science ABSTRACT Sunlight is the primary energy source to drive photosynthesis, as well as the signal to stimulate series of developmental events ranging from germination to flowering in plants. Light can induce leaf formation, leaf expansion, and chloroplast differentiation, and inhibit stem elongation. Light has great impact on turfgrass quality and turfgrass performs best with a minimum of four to six hours of full sun per day. However, under certain circumstances, a grassed area may be shaded for most or all of the day, making it a problem for turfgrass to obtain enough light energy. Modern stadiums create a shaded environment that requires turfgrass for sports usage, while some area of a semi-enclosed arena receives little or no direct sunlight especially during winter season. Moreover, when sunlight penetrates the canopies and reaches the surface of the turf, both light quantity and quality (red/far-red ratio) drop dramatically. Shade stress causes succession of harmful physiological and morphological changes in plants, such as thinner, more delicate leaves, reduced tillering, poor shoot density, altered pigment concentration, and affected carbohydrate reserve. Moreover, it is difficult for turfgrass to recover from wear under shade. Vertical growth remains a critical problem in turfgrass management. Practical methods can be used to control the plant growth. For example, application of chemical regulators can inhibit gibberellin (GA) biosynthesis and reduce the stem ii growth. Alternatively, improving the characteristics of cultivars by biotechnology is a long-term option. GA 2-oxidase (GA2ox) genes are important in control of GA levels. Overexpression of OsGA2ox causes a dwarf phenotype and delay in reproductive development in transgenic rice. Moreover, genetic engineering of phytochrome genes has provided a potential means to control vegetative growth and reproductive development. Phytochrome represents a family of red-light-absorbing photoreceptors that exist in the physiologically inactive Pr form and the active Pfr form. Transformation and overexpression of the PHYB gene in Arabisopsis and tobacco resulted in a dwarf phenotype. Additionally, BAS1 is a gene regulating brassinosteroid (BR) levels and light responsiveness in Arabidopsis. Overexpression of the BAS1 gene leads to decreased BR levels and a BR-deficient dwarf phenotype. The objectives of our studies were: 1) develop creeping bentgrass plants transformed with GA2ox gene from runner bean (Phaseolus coccineus), BAS1 gene from Arabidopsis, and PHYB1 gene from tobacco (Nicotiana tabacum), respectively; 2) evaluate growth responses of transgenic plants under various light conditions and reveal possible interactions between hormones and photo-receptors. Our results showed that vertical growth, internode extension, and leaf growth of transgenic creeping bentgrass plants were inhibited by GA2ox transformation under reduced low light conditions in the field. True GA2ox gene transformants showed increase in overall quality, shoot density, or stolon density compared with control plants. Moreover, GA2ox transgenic lines tended to keep horizontal growth habit, possibly due to the increased GA metabolism by GA2ox overexpression, or the collaborated work of GA and light receptors in signal transduction. Greenhouse studies revealed the similar results to field studies. Strong transformants, such as iii GA6548 and GA6549, displayed dwarfism and superior quality under all light conditions. RT-PCR results confirmed that mRNA level of foreign GA2ox was correlated with the selection indices ranking of creeping bentgrass plants both in the greenhouse and the field. Furthermore, reduction in R:FR increased vertical growth and erectness of both PHB1 gene transformants and control plants. As group, transgenic plants exhibited delayed vertical shoot growth and more horizontal shoot architecture, but did not demonstrate significant change in leaf growth or visual quality. PB0701 exhibited highest visual quality and lowest leaf growth rate among all plants. Leaf growth was observed to be affected mainly by the change of PPF rather than R:FR. Visual quality rating increased with the rise of both PPF and R:FR. RT-PCR results revealed the transcription of PHYB1 gene in all creeping bentgrass lines, with PHYB1 transformant PB0701 displayed highest transcription level. It may also be associated with its high quality and alleviation of shade response under low light conditions. Finally, reduction in R:FR increased vertical growth and erectness of both BAS1 gene transformants and control plants, however, overexpression of BAS1 gene induced dwarfism in transgenic creeping bentgrass by delaying vertical shoot growth and altering shoot architecture. True BAS1 transformants (BS1305, BS1307, BS1701) had the best performance in most traits even under reduced PPF and R:FR. iv To my parents Benxiu Yan and Aihua Zhang my husband Hailu Meng Thank you for the support and dedications v ACKNOWLEDGMENTS My dream may never come true without the support of many intelligent people. I would like to extend my sincere appreciation to my major advisor Dr. Karl Danneberger for his support, guidance, encouragement, and friendship. It has been wonderful experience working with Karl for the past five years. I am also indebted to Dr. David Gardner, Dr. Lisa Lee, Dr. Jim Metzger, and Dr. Guoliang Wang for serving on my committee and providing continuous and generous support. Special thanks to Dr. Bo Zhou and other members in Dr. Guoliang Wang’s lab, to Craig Yenkrek, Adri McKelvey, and other members in Dr. Jim Metzger’s lab, to Pam Sherratt, Jill Taylor, and other turf group members for their support, assistance, and friendship. I am also grateful to Dr. Bob Harriman, Dr. Eric Nelson and other scientists in Scotts Company for their training and support. To Mom and Dad: I want to thank both of you for teaching me the value of diligence and devotion, and for supporting me constantly. To Hailu: Thank you for your consideration and encouragement during my most stressful time. You are a great companion during the long and tough journey. vi VITA February 24, 1978.................Born – Maanshan, Anhui Province, China 2001………………………...M.S. Biology, Nanjing University, Nanjing, China 2001-Present……………......Graduate Research Associate, The Ohio State University PUBLICATIONS Referred Journal Articles Yan, J., J. Li, Y. Xu, and J. Zhang. 2001. Studies on situations, causes and controlling strategies of ecological pollution in Nanjing City. Urban Environment & Urban Ecology 14:36-38. FIELDS OF STUDY Major field: Horticulture and Crop Science Specialization: Turfgrass Physiology and Ecology Turfgrass Molecular Breeding vii TABLE OF CONTENTS Page Abstract ………………………………………………………………………. ii Dedication ……………………………………………………………………. v Acknowledgements …………………………………………………………. vi Vita …………………………………………………………………………. vii List of Tables ………………………………………………………………… x List of Figures ………………………………………………………………... xi Chapters 1. Literature review…………………………………………………………. 1 Creeping Bentgrass……………………………………………………… 1 Genetic Transformation of Creeping Bentgrass………………………….. 2 Shade Studies Review…………………………………………………… 4 Phytochrome B Review…………………………………………………… 8 Gibberellin Review………………………………………………………. 13 Brassinosteroid Review…………………………………………………… 21 References…………………………………………………………………. 27 2 Field and greenhouse evaluation of transgenic creeping bentgrasses transformed with runner bean GA2ox gene………………………………… 43 viii Abstract…………………………………………………………………….…. 43 Introduction……………………………………………………………….…. 44 Materials and Methods………………………..……………………………… 47 Results………………………………………………………………………... 54 Discussion…………………………………………………….……………… 60 References…………………………………………………………………… 79 3 Development and characterization of transgenic creeping bentgrass transformed with tobacco PHYB1 gene……………………………………… 83 Abstract…………………………………………………………………….…. 83 Introduction………………………………………………………………….. 84 Materials and Methods……………………………………………………….. 86 Results…………………….………………………………………………….. 90 Discussion……………………………………………………………………. 94 References……………………………………………………………………. 108 4 Development and characterization of transgenic creeping bentgrass transformed with Arabidopsis BAS1 gene……………………………………. 113 Abstract…………………………………………………………………….…. 113 Introduction………………………………………………………………….. 114 Materials and Methods……………………………………………………….. 115 Results……………….……………………………………………………….. 120 Discussion……………………………………………………………………. 122 References……………………………………………………………………. 132 ix LIST OF TABLES Table Page 2.1 Vertical growth rate, internode length, and leaf length of 40 creeping bentgrass cultivars under neutral shade, canopy shade, and full sun in 62 the field.…………………………………………..…………………….. 2.2 Visual quality, shoot density, and stolon density of 40 creeping bentgrass cultivars under neutral shade, canopy shade, and full sun in 64 the field ……………………...………………………………………….. 2.3 Color and erectness of 40 creeping bentgrass cultivars under neutral shade, canopy shade, and full sun in the
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