Project: Designing starch: harnessing carbohydrate polymer synthesis in plants
Starch is a natural product produced by most land plants and algae with remarkable physico-chemical properties. Starch is composed of two polymers of glucose: amylose, a predominantly linear polymer of α-1,4 linked glucose units, and amylopectin, which also contains α-1,6 linkages (branch points) resulting in a tree-like structure. The simple constituents of starch (one type of monomer and two types of linkages) is contrasted by its complex and highly ordered structure, in which crystalline and amorphous layers alternate in a defined and regular fashion. This structure gives starch unique physicochemical properties, which make it an exceptionally tightly packed energy storage that is of such tremendous importance for the human diet and economy as a whole. Despite decades of intense research, it is still not understood how precisely starch granule biogenesis initiates and progresses. A relatively small number of enzymes are involved, but it is unclear how their activities are coordinated in order to ultimately control the structure and properties of starch. The objective of our project is to gain a profound understanding of the regulation and control of the biophysical and biochemical processes involved in the formation of the complex polymeric structure that is the starch granule. We will apply this understanding to recreate the synthesis of starch in vitro and learn to control its physical and chemical properties in a targeted way. By expressing starch synthesising enzymes in yeast, an organism not natively producing starch, we will design starches with desired properties in vivo. This will be translated back in planta to genetically engineer plants producing starch with desired, pre-defined physico-chemical properties. To achieve our goal, we will simultaneously follow bottom-up and top-down approaches, complemented by synthetic and theoretical biology activities. We will systematically analyse the components of the starch synthesis systems by characterising all involved enzymes in vitro in order to understand their functional specialisations (WP1). These data will inform the mathematical models (WP4) used to predict the combined actions of enzymes in vitro (WP1) and the behaviour of engineered pathways in vivo (WP2&3). The characterised components (WP1) will be used to engineer starch synthesis in Saccharomyces cerevisiae (WP2). Using controllable promoters, we will systematically regulate the levels of individual enzymes, allowing the production of insoluble polymers to be fine-tuned, thereby testing test model predictions (WP4) and forming the basis for the transformation of plants (WP3). In summary, we will generate a systems-wide understanding of the synthesis of the complex starch polymers and implement design strategies to create starches with desired properties in vitro and in vivo.
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