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  Modulating seed size in oilseed rape

Seed size plays a key role in the yield, quality and profitability of oilseed rape (Brassica napus), with ancillary effects on the early stages of crop establishment through its contribution to seedling vigour. In this project we will test the hypothesis that specific mechanisms that have been found to regulate seed size in the Brassicaceae reference species Arabidopsis are able to provide a route to significant increases in seed size in the related Brassica crop species. We are able to capitalise on a unique combination of recent findings in Arabidopsis, together with access to genetic and genomic tools for comparative analysis in Brassica. In particular, we will determine which specific developmental mechanisms contribute to existing natural variation within the Brassica genepool, and account for the observed variation in seed size. We will then test the hypothesis that Brassica orthologues of specific candidate genes that are up-regulated in 'large' seeds of Arabidopsis and are either not up-regulated or are down-regulated in 'small' seeds are also responsible for seed size variation in Brassica. The information and insights we obtain will be available for use in developing gene-specific molecular markers to screen allelic diversity within Brassica genepools. This will facilitate identification of valuable alleles for exploitation in breeding programmes aimed at boosting seed size and yield.

The specific objectives are to:
1. Identify developmental mechanisms that control final seed size in Brassica
2. Assign known variation in Brassica seed size to specific mechanisms
3. Test the hypothesis that early endosperm proliferation due to paternal excess can contribute to significant increases in Brassica seed size
4. Test the hypothesis that gene(s)/alleles on specific chromosomes of the oilseed rape C genome contribute to variation in seed size.
5. Test the ability of candidate genes to modulate seed size in Brassica

  Molecular biology of embryo development and germination

For seed development to proceed the expression of a large number of genes is co-ordinately controlled in response to an array of developmental signals. These signals control embryogenesis, embryo maturation and germination and the transition from one phase of development to another. Of particular interest is the transition from the embryo maturation phase to the germination phase, and the separation of embryogenic and vegetative development.

Our objective is to identify loci essential for germination, which would potentially be involved in the regulation of dormancy, desiccation tolerance, the initiation of vegetative development, and the mobilisation of energy reserves.

To this end we have screened for germination mutants in a population of Arabidopsis seeds subjected to fast neutron bombardment. Eight mutant lines with a reduced germination potential were selected for further study. One line, mutated at the locus we have called COMATOSE (CTS), has been partially characterised. Genetic analysis of CTS indicates that the phenotype is only expressed in the embryo (Development 127: 3769-3767 (2000)).

  Molecular cell biology of plant development

Our objective is:
a) To identify new loci in Arabidopsis that play a role in the cellular development and specification of cell fate, with emphasis on embryogenesis and meristem development.
b) To understand signalling cues that establish developmental patterns.

Plant development depends on asymmetric cell division. The final form of plants is due to different patterns of cell division and cell expansion. The control of plant development is determined both by cell lineage and positional information from individual cells. The basic features of a plant’s body plan are established during embryogenesis. Embryo and seed development are vital developmental processes, but very few transcription factors that regulate these stages are known. The use of targeted gene expression, enhancer trap lines and marking developmental stages during embryogenesis will help identify new candidate genes that play a major role in embryo, seed and meristem development. These studies are designed to identifiy genes or regulators that are expressed at a particular developmental stage and facilitate elucidation of the function of these regulators.

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  Genomic and epigenetic regulation of Brassica oilseed traits

Brassica oilseed rape is the primary renewable vegetable oil grown in N. Europe and the main break crop in the cereal rotation, grown on increasing acreage in the UK. The variety of food and non-food end uses require continuity of supply, with consistent high yield and predictable seed composition. These need to be achieved with reduced levels of inputs and in variable growing environments.
The project integrates several approaches to develop an understanding of the genes and mechanisms underlying regulation of key traits affecting oilseed yield and composition.

Specific targets:
1. Using comparative genomics and quantitative genetics to resolve loci affecting seed development and associated traits
2. Establishing how the rate of seed development affects harvestable seed size and quality
3. Determining how epigenetic processes affect plant development in different environments

  Regulation of plant phospholipid biosynthsis

Phospholipids are essential for the construction of eukaryotic cell membranes, which play a fundamental role in compartmentalising the biochemistry of life. The quantity and composition of phospholipids are tightly regulated during growth and development, and in response to environmental change, so that membranes always maintain their structure and function. Research in mammals and yeast has uncovered elegant metabolite signalling mechanisms, both transcriptional and post-translational, that allow the cell to sense changes in key lipid intermediates and adjust phospholipid synthesis (and turnover) accordingly. Analogous mechanisms are also likely to exist in plants but surprisingly they have not been elucidated. We have recently isolated an Arabidopsis thaliana double mutant in two phosphatidate phosphatases (pah1 pah2) that produces approximately twice as much phospholipid in its leaves as wild type plants. The objective of this work is to use the pah1 pah2 mutant (and corresponding genes) to discover how phospholipid biosynthesis is regulated in Arabidopsis and to investigate how it is coordinated with cell cycle progression, which requires membrane biogenesis.

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