Increasing Oil Content by Redirecting Carbon Flux During Seed Development – SYNERGY (Seeds Yield eNERGY)

Genetic screens are labour intensive and so we will develop novel technology to increase the efficiency of screening for regulatory genes by the use of a combination of a fluorescent reporter and a powerful positive or negative selectable marker under the control of genes linked to the synthesis of seed reserves. This selection strategy will minimise effort and cost and allow us to perform several complementary screens for genes controlling carbon partitioning, for example screens that allow isolation of components of regulatory complexes via protein-protein interactions or regulatory factors that act in the same or alternative pathways as certain master regulatory genes that control many aspects of seed development including the synthesis of oil and protein reserves.
We will conduct Protein-DNA interaction screens in yeast to isolate plant genes which directly control storage oil synthesis. Screening large populations of mutagenised Arabidopsis plants has proved a successful approach to isolate genes that alter oil content in seeds which we will adopt by optimising and extending this type of screen to new collections. This type of screen has allowed us to characterise mutations that affect carbohydrate synthesis in the seed coat and result in increased oil content in the embryo.
We will investigate the relationship between carbohydrate metabolism, seed size and seed oil content by deciphering the regulation of genes that control the synthesis of carbohydrate to provide an understanding of how genes expressed in the seed coat in influence oil accumulation in the embryo. This knowledge of the network of genes controlling carbohydrate synthesis in cell walls and seed coats of Arabidopsis will allow us to silence similar genes in Camelina sativa in the expectation to increase oil yield in this non-food crop emerging as a platform for industrial oils.

At the conclusion of the project, we expect to have developed prototype Camelina sativa lines with improved oil yield for biodiesel production and /or industrial applications as a proof of concept of the SYNERGY project. Significant scientific results from this project are expected to include the identification of novel protein factors that control reserve accumulation in seeds and insight as to how these factors integrate into a regulatory network that controls the synthesis and accumulation of reserves in seeds. An understanding of the mechanism of how carbon assimilated by the plant during photosynthesis is converted into carbohydrate, lipid and protein in the developing seed will aid engineering and selection of cultivated plants with a greater yields of oil or protein in seeds. We therefore expect that the results generated in the SYNERGY project will be of value to understand the mechanisms of regulation of carbon partitioning into sugar, starch, lipid and protein among reproductive tissues (fruit, seed coat, endosperm, embryo) and also in vegetative tissues (leaves stems, tubers and roots).
Our early results include the isolation of putative regulators of genes that are important in the control of oil biosynthesis and the identification of a large number of seeds from mutated Arabidopsis lines that seem to have high or low amounts of oil.

The research in the SYNERGY project lays the foundation for the creation of high yielding oilseed non-food crops that are agronomically successful on marginal land. The creation of novel oilseed crops will increase the supply of vegetable oils independent of the food supply chain thereby facilitating the expansion of biodiesel that will in turn aid greenhouse gas mitigation. We anticipate that this will lead to an increased use of Brassica oil as a renewable heavy transport fuel with a positive effect on the environment by reducing greenhouse gases and the use of fossil fuel. We believe that the project will have a further impact on the potential for energy densification in plant biomass and the production of high value products in seeds.
Transfer of the knowledge and genes resulting from the SYNERGY project to conventional oilseed crops will alleviate the food-fuel conflict by increasing the availability of vegetable oils for human and animal nutrition. By isolating factors that control carbon partitioning between oil and protein we should be able to increase either reserve to eventually obtain high oil-low protein or low oil-high protein seeds depending on the intended use of the crop.

Poster:
Dean G, Shi L, Roscoe T, Devic M, Smith M, Haughn G, Kunst L. (2013) Investigating the links between oil accumulation and seed coat development in Arabidopsis and Camelina. Gordon Research Conference, Plant Lipids: Structure, Metabolism & Function Galveston, USA January 26-27, 2013.

This poster explains how mutations in genes that control the synthesis of mucilage in the seed coat lead to an increase in oil content of the seed of Arabidopsis, a model plant. Knowledge of these genes allows us to reduce the production of mucilage in the seed coat of Camelina sativa, an emerging non-food oil crop, to increase oil yield in the seed. We also describe how we screen seeds for high or low oil content.

There are urgent environmental and economic imperatives to develop renewable sources of energy for heat, electricity and transport fuels. Bioenergy in the form of biomass and biofuels, will constitute an increasingly important component for sustainable energy only if their production does not compromise land use for food production and that an ecological and carbon neutrality is assured. For liquid transportation fuels, biodiesel derived from the triacylglycerols of oilseed crops is preferred over starch or sugar-derived ethanol because of its greater energy density per volume and more efficient energy conversion of feedstocks. A barrier to a more widespread adoption of biodiesel is associated with the cost and limited supply of seed oils. Therefore, to alleviate the problem of an increased demand for vegetable oil production for nutritional, industrial and biodiesel uses it is essential to improve oilseed yields. One approach to enhancing oil yield would be to alter the partitioning of carbon in seeds to favour the synthesis of triacylglycerol over storage protein and other seed components. Such an approach requires knowledge of the genetic determinants governing seed development and reserve accumulation in seeds.

The aim of the SYNERGY project is to investigate the extent to which carbon can be re-directed from structural and other reserve components of the seed to triacylglycerol in order to enhance oil yield in a model oilseed plant combined with the perspective to translate this knowledge to emerging non-food crop platforms which are performant on marginal land. The specific objectives are to identify and characterise novel transcriptional regulators of seed oil synthesis and assess their ability to influence carbon partitioning between oil and protein. Secondly, elucidate gene regulatory networks controlling specific metabolic pathways in the seed coat and to determine the extent to which altering metabolism in the seed coat alters the metabolic fate of carbon assimilate during seed development.

By isolating and characterising transcription factors that control the expression of acyltransferases essential for triacylglycerol synthesis in seeds, the SYNERGY project will address our lack of knowledge of the regulation of the genes that control triacylglycerol assembly. The genetic screens employed will lead to the identification of factors that will include novel transcriptional regulators, co-regulators and repressors that control both the production of fatty acids destined for TAG assembly and those that control seed storage protein synthesis. Genetic dissection of the gene regulatory network controlling the expression of the high seed oil mutant glabra2 will lead to an understanding as to the transcriptional control of the pathway of mucilage synthesis in the seed coat and insight to the signalling of carbon repartition to lipid synthesis in the embryo during development. With this knowledge we will be in a unique position to test the engineering of seed oil content by re-directing carbon flow from diverse metabolic products of the seed. Candidate genes anticipated to be of interest for increasing seed oil content will be transferred to Camelina sativa. The translational biology component of the project adds value to the fundamental research that underpins SYNERGY programme since it will represent a validation of this emerging industrial crop platform.

In conclusion, we expect to identify novel regulators of fatty acid modification, triacylglycerol assembly and storage protein synthesis and we expect to elucidate the influence of seed coat expressed factors AP2, TTG1, TTG2 and GL2 and their relations with FUS3 on oil synthesis in embryo. We anticipate that knowledge acquired during the SYNERGY project will lead to the development of novel oilseed platforms engineered for enhanced seed oil content.