Designing starch: harnessing carbohydrate polymer synthesis in plants

淀粉是大多数陆生植物和藻类的天然产物，具有显著的理化性质。淀粉由两种葡萄糖聚合物组成：直链淀粉和支链淀粉，直链淀粉是一种主要由α -1,4连接的葡萄糖单元组成的线性聚合物，支链淀粉也含有α -1,6连接（分支点），形成树形结构。淀粉的简单成分（一种单体和两种键）与其复杂而高度有序的结构形成鲜明对比，其中晶体层和非晶态层以明确而规则的方式交替存在。这种结构赋予淀粉独特的物理化学性质，使其成为一种非常紧密的能量储存方式，对人类的饮食和整体经济都具有巨大的重要性。尽管经过几十年的深入研究，人们仍然不清楚淀粉颗粒的生物发生是如何精确地开始和发展的。相对较少的酶参与其中，但目前尚不清楚它们的活动是如何协调的，从而最终控制淀粉的结构和性质。我们项目的目标是深入了解复杂聚合物结构淀粉颗粒形成过程中涉及的生物物理和生化过程的调控。我们将运用这一认识在体外重建淀粉的合成，并学习有针对性地控制其物理和化学性质。通过在酵母（一种不产生淀粉的生物）中表达淀粉合成酶，我们将在体内设计出具有所需特性的淀粉。这将在植物中转化为基因工程植物，生产具有所需的、预先定义的物理化学特性的淀粉。为了实现我们的目标，我们将同时遵循自下而上和自上而下的方法，辅以合成和理论生物学活动。我们将系统地分析淀粉合成系统的组成部分，通过表征所有涉及的酶在体外，以了解他们的功能专门化（WP1）。这些数据将为数学模型（WP4）提供信息，用于预测酶在体外的联合作用（WP1）和体内工程途径的行为（WP2&3）。所表征的组分（WP1）将用于在酿酒酵母（WP2）中进行淀粉合成工程。使用可控启动子，我们将系统地调节单个酶的水平，允许不溶性聚合物的生产进行微调，从而测试测试模型预测（WP4）并形成植物转化的基础（WP3）。总之，我们将对复杂淀粉聚合物的合成产生系统范围的理解，并实施设计策略，以在体外和体内创造具有所需性能的淀粉。

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 alpha-1,4 linked glucose units, and amylopectin, which also contains alpha-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.