- Title
- Genetic regulation of embryo development and formation of seed storage products in the legume model Medicago truncatula
- Creator
- Song, Youhong
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2013
- Description
- Research Doctorate - Doctor of Philosphy (PhD)
- Description
- Legumes are increasingly recognised as playing a critical role in addressing the food crisis and meeting growing demands for bioenergy in a framework of sustainable cropping. M. truncatula is a widely used model to study legume biology particularly for legume-specific developmental questions such as nodulation. Accordingly, rich genetic sequencing information and extensive databases with bioinformatic analyses are made available by the legume community. This facilitates the use of M. truncatula as a model to study legume seed biology. A global picture of proteomics and transcriptomics of M. truncatula seed filling has been explored. However, there is still limited information available for M. truncatula as a legume model for studying seed biology and seed filling. This study in the thesis characterised M. truncatula embryo development from embryo sac to protein and oil body formation using histological, biochemical and molecular methods. A multicellular hypophysis, suspensor development and a clear procambial connection between shoot and root apical meristems are featured. TEM images clearly show a specific oil body arrangement aligning the protein bodies and plasma membrane. Gene expression during early seed development and the accumulation of storage protein and oil was profiled, with a focus on transcription factors. Embryogenesis establishes the embryonic pattern that acts as the centre for growth after germination and develops the cotyledons that are a repository for protein bodies and oil bodies in legumes. Early embryogenesis with a series of complex development events is completed in 6-8 days and is tightly regulated by a network of transcription factors. Early embryogenesis is characterised by three distinctive expression patterns, with MtSERF1 and MtWOX9 expression associated with embryo growth, connecting the early and late embryo development. Medicago orbicularis was chosen to compare the accumulation of seed storage products with M. truncatula because of its lower seed protein and oil. Further biochemical and histology studies clearly showed a contrasting seed nutritional spectrum in terms of protein, oil, starch and cell wall between M. truncatula and M. orbicularis, which provides a pair of close species to investigate genetic mechanisms of seed storage accumulation. The major regulators of seed maturation and seed filling are LEC1/L1l, LEC2, FUS3 and ABI3 in Arabidopsis while in Medicago only L1L and ABI3 are shown to be possible equivalent regulators. The expression of selected pathway genes further confirmed the transcriptional regulation. Reduced oil content in M. orbicularis is also associated with increased seed coat mucilage and cotyledon cell wall material, and gene expression of associated biosynthetic pathways. The storage compounds can potentially be influenced by modifying carbon flow (e.g. the mucilage biosynthesis pathway), or modifying regulatory genes (e.g. L1L). Apart from the biosynthesis of protein and oil, the process of packing protein and oil is also important for the final storage in the cotyledons. A highly efficient plant transformation system is essential for gene functional analysis and creating transgenic lines. Accordingly, an improved transformation procedure was developed using a new hormonal combination of ABA+GA (an unusual synergism) imposed from the beginning of tissue culture. In essence, the study in this thesis completed a detailed examination of morphological, cellular and molecular aspects of embryogenesis in M. truncatula, providing a legume perspective to complement studies in Arabidopsis embryogenesis. By comparing the cellular, biochemical and molecular basis of seed storage between M. truncatula and M. orbicularis, these species were found to be a promising pair for investigating mechanisms of regulating partitioning of legume seed storage compounds. The improvement of transformation efficiency further facilitates the genetic modification of specific genes of interest in M. truncatula in this context. Therefore, this thesis lays a foundation for further studies in legume seed biology and the regulation of seed filling and storage partitioning.
- Subject
- legumes; Medicago truncatula; legume tissue culture; legume transformation; GA and ABA; somatic embryogenesis; zytotic embryogenesis; embryogenesis; Medicago orbicularis; seed/ovule development; seed maturation and genetic regulation; oil and protein storage; oil body and protein body; oil and protein partitioning; transcriptional regulation; mucilage
- Identifier
- http://hdl.handle.net/1959.13/1036769
- Identifier
- uon:13358
- Rights
- Copyright 2013 Youhong Song
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT02 | Thesis | 10 MB | Adobe Acrobat PDF | View Details Download |