Award details

Elucidating the mechanism of starch granule initiation in developing wheat grains

Reference	BB/P010814/1
Principal Investigator / Supervisor	Dr David Seung
Co-Investigators / Co-Supervisors
Institution	John Innes Centre
Department	Metabolic Biology
Funding type	Research
Value (£)	304,886
Status	Completed
Type	Fellowships
Start date	01/05/2017
End date	31/12/2018
Duration	20 months

Abstract

Little is known about the mechanisms that initiate starch granule synthesis in plastids of higher plants. A breakthrough was achieved when I revealed a suite of previously uncharacterised "initiation proteins" required for normal granule initiation in Arabidopsis leaf chloroplasts. These initiation proteins are conserved among higher plants, including cereal crops such as wheat, and are expressed in the endosperm during grain development. It is unknown how they influence granule initiation in developing wheat grains, where initiations occur in two temporally-separate waves during grain filling - the initial wave forming large A-type granules, and the later wave forming smaller B-type granules. The aim of my proposed work is to elucidate the molecular mechanism of granule initiation in the wheat endosperm, using the initiation proteins as a starting point. Firstly, I will characterise the function of initiation protein orthologs in A- and B-type granule initiation in hexaploid bread wheat by isolating TILLING mutants deficient in these proteins. Granule initiation phenotypes will be observed during grain filling using electron microscopy and biochemical techniques. Secondly, as the initiation proteins contain coiled-coils that can mediate protein-protein interaction, I will use co-immunoprecipitation and mass spectrometry to discover interaction partners of the initiation proteins in wheat amyloplasts. These new candidate proteins will be characterised by isolating and analysing wheat TILLING mutants deficient in these proteins, as above. Finally, I will investigate the potential of exploiting starch granule initiation genes to modify industrially-relevant starch properties, by measuring gelatinisation temperature, gel viscosity and digestibility of starch in the wheat mutants. This research has important future implications for improving the quality of wheat, providing modified starch properties for the industry as well as resistant starch for a healthier diet.

Summary

Despite its importance to humankind, we still do not fully understand how starch is made in plants. Starch is a complex carbohydrate that is composed of a large number of glucose units joined together into polymers, and is produced by plants as an energy store. It is found in leaves of most plants where it provides energy for growth at night, but it also accumulates in large amounts in many of our staple foods, such as wheat, rice and potato. Starch is therefore a major component of our diets, but it is also essential in manufacturing a variety of everyday items such as paper, textiles and pharmaceuticals. A full understanding of how plants make starch will lead to new ways of improving the nutritional value of our staple foods, with added health benefits, and also improving the quality of starch used for manufacturing. The polymers in starch assemble into insoluble 'granules'. While we have a good understanding of how the polymers in starch are synthesised, we do not yet understand how the process of making the starch granule begins in the plant. Without this knowledge of the granule initiation process, we can not understand what controls the number of granules that are made. The number of granules affects the size and shape of granules, which strongly influences how starch behaves during digestion, and also during manufacturing processes. Over the last decades, researchers have been using the model plant, a small weed named Arabidopsis thaliana, to better understand the starch synthesis process. Recently, I have made a breakthrough in understanding starch granule initiation in Arabidopsis leaves, and identified several new proteins involved in the process. Interestingly, all of these proteins are also present in other plants, including our staple crops such as wheat. Therefore, it is now time to move beyond the model and apply this new knowledge to our crops. The aim of this project is understand how starch synthesis is initiated in developing wheat grains. Using the latest advances in wheat genetics and breeding, I will find wheat mutants that do not have functional versions of the newly-discovered proteins involved in granule initiation. I will then study how the pattern of granule initiation changes within the developing grain as a result of the mutation. In parallel, I will also aim to discover new proteins involved in initiating starch granules in the grain by finding other proteins that bind to the existing ones. I will also study whether the wheat mutants have altered starch properties that are important for manufacturing food and non-food products. This will include tests for whether the flour milled from the grains have altered digestibility, which may alter the calorific value of foods. This research will contribute to the development of innovative crops in the UK, as it will lead to the development of new wheat varieties with altered starch properties that are healthier to eat, or of higher quality for use in manufacturing.

Impact Summary

The wider public will benefit from my proposed research, as they are ultimately the end consumers of food and non-food products of wheat starch. This research falls into the BBSRC's research priority of 'Agriculture and food security,' because understanding starch synthesis in the UK's major crop will lead to innovative ways to optimise starch quality for different end uses. Achieving food security is not only about increasing crop yields, but also about improving the quality of the crop. The latter is important for reducing waste and optimising productivity in subsequent manufacturing processes, thus minimising additional energy inputs. My research will also address BBSRC's priority for 'Bioscience for health', because alterations in starch digestibility can lead to wheat with altered nutritional value and health benefits, such as increased resistant starch. Therefore, the benefits passed on to the UK public will be in the area of food security, sustainability and health. Since these issues resonate globally, the research will have similar impacts abroad, and will be applicable to other starch crops. The wheat mutants generated in this project, as well as the method of altering starch properties by targeting granule initiation genes, will attract interest from industry. Specifically, the starch processing industry will benefit from having novel wheat starches with altered properties (e.g: lower gelatinisation temperature, or decreased size variation) that are more economically processed. The manufacturing industries that utilise starch (e.g: paper-making, textiles and pharmaceuticals) will also benefit from having access to starch with altered properties that better suit end-use requirements. The food industry will also benefit if the observed changes in starch properties improve the quality of the product (e.g. better mouthfeel, taste, or improved economy of manufacture). If the digestibility of starch has been altered, this would greatly interest food manufacturers aiming to produce healthier wheat-based foods. Representatives from these industries will be engaged in discussions regarding results and outcomes of my project (see Pathways to Impact). Holding these consultations will in itself have a positive impact for both JIC and the companies, as collaborations between academia and industry is important for continued innovation. Wheat breeders and farmers will benefit from wheat crops with altered starch properties if the public and/or industries create demand for such wheat products with the benefits listed above. This will raise the value of the crop, which in the short-term could benefit growers. The continued development of new varieties with novel traits will have positive impacts on the UK wheat industry in terms of economic competitiveness, and will be viewed as innovative by the rest of the world. Beyond wheat, this research is applicable to other starch crops - including orphan crops of the developing world, in which modified starch properties could generate business opportunities, and thus provide increased income for farmers. Academic researchers in various fields of biology will benefit from this research (see Academic beneficiaries). The mechanism of granule initiation is likely to involve concepts that are of common interest to all cell biologists and biochemists, and the research will be communicated to them through publications and conferences. As an academic researcher myself, I will also benefit from the training opportunity this fellowship offers, particularly in transferable skills important for establishing independent research. I will also develop specific scientific skills that I require for addressing future research goals (see career development plan). Furthermore, I will train students in the laboratory and involve myself in teaching during the fellowship. This will ensure further training of skilled people in plant biology, thus contributing to the UK knowledge economy.

Committee	Research Committee B (Plants, microbes, food & sustainability)
Research Topics	Crop Science, Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	Fellowship - Future Leader Fellowship (FLF) [2014-2015]
Funding Scheme	X – not Funded via a specific Funding Scheme

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