Unravelling novel mechanisms of starch granule biogenesis in potato

本计画将发展马铃薯块茎发育过程中淀粉粒形成的机制。淀粉是植物储存碳水化合物的主要形式，并且作为我们饮食中的主要卡路里来源对人类至关重要。尽管它的重要性，我们仍然不完全了解植物如何产生淀粉。在其天然形式中，淀粉形成由葡萄糖聚合物组成的不溶性颗粒。颗粒的大小在物种之间变化很大，并影响淀粉在烹饪过程中的物理和化学行为，以及最终食品的质地。最近，我们已经取得了突破性进展，了解淀粉颗粒启动（或引发）的模式植物，拟南芥的叶片，并在谷物颗粒的机制。在这些植物中，颗粒大小受每个质体起始的颗粒数量的影响。然而，尚未研究马铃薯中的颗粒起始，马铃薯在淀粉作物中含有最大的颗粒尺寸。从其他物种中获得的知识使其特别及时地发现马铃薯中颗粒大小和数量的控制。此外，马铃薯淀粉颗粒具有明显的椭圆形，但决定颗粒形态的过程在任何物种中都不清楚。本项目旨在发现淀粉颗粒起始和形态发生的分子机制。首先，我们将研究哪些颗粒起始蛋白建立正确的颗粒数量和大小在发展块茎，通过创建和研究一系列的突变体缺陷的每个起始蛋白。然后，我们将测试的假设，有活跃的颗粒形态发生在马铃薯，根据初步数据，这一过程需要一个特定的起始蛋白亚型。最先进的3D电子显微镜和荧光显微镜将用于研究淀粉体的结构（合成和储存淀粉的质体细胞器）-显示每个造粉体通常有多少颗粒起始，每个细胞的造粉体数量，以及新颗粒的形成如何与新造粉体的形成协调。作为促进进一步影响的最终目标，我们将使用本项目过程中产生的独特材料来评估颗粒大小和形态对淀粉在烹饪过程中的物理和化学行为、淀粉消化率以及各种马铃薯食品的质地和感官质量的影响。总的来说，该项目将极大地推进我们对马铃薯淀粉粒生物合成基本机制的理解。

This project will develop a mechanistic understanding of starch granule formation in developing potato tubers. Starch is the major form in which plants store carbohydrates, and is vitally important to humankind as a major source of calories in our diet. Despite its importance, we still do not fully understand how plants produce starch. In its native form, starch forms insoluble granules that are composed of glucose polymers. The size of the granules is highly variable between species, and influence the physical and chemical behaviour of starch during cooking, as well as on the texture of the final food products. Recently, we have made breakthroughs in understanding the mechanism by which starch granules are initiated (or primed) in leaves of the model plant, Arabidopsis thaliana, and in cereal grains. In these plants, granule size is influenced by the number of granules initiated per plastid. However, granule initiation has not been investigated in potato, which contains the largest granule sizes among starch crops. The knowledge gained from other species make it particularly timely to discover the control of granule size and number in potato. Further, potato starch granules have a distinct ellipsoid shape, but the processes that determine the morphology of the granules are not understood in any species.This project aims to discover molecular mechanisms of starch granule initiation and morphogenesis. Firstly, we will investigate which of the granule initiation proteins establish correct granule number and size in developing tubers, by creating and studying a series of mutants defective in each initiation protein. We will then test the hypothesis that there is active granule morphogenesis in potato, based on preliminary data that this process requires a specific initiation protein isoform. State-of-the-art 3D electron microscopy and fluorescence microscopy will be used to study the structure of amyloplasts (the plastid organelle in which starch is synthesised and stored) in detail through tuber development - showing how many granules are typically initiated per amyloplast, the number of amyloplasts per cell, and how new granule formations are coordinated with new amyloplast formation.As a final objective to facilitate further impact, we will use the unique materials generated through the course of this project to assess the effects of granule size and morphology on the physical and chemical behaviour of starch during cooking, starch digestibility, as well as textural and sensory qualities in a variety of prepared potato food products. Overall, this project will greatly advance our understanding of fundamental mechanisms of starch granule biogenesis in potato.