David’s research group aims to develop a full molecular understanding of how plants make starch.
Starch plays a crucial role in plants as the major form of carbohydrate storage. Most plants use starch reserves to generate metabolic energy in the dark when photosynthesis is not possible. Growth of plants during the night, or of seedlings underground before they emerge from the soil, is often fuelled by starch.
As one of the most important plant products in our daily lives, starch is all around us. It is the major calorific component of our staple foods, such as wheat, rice and potatoes. It is also an important ingredient in manufacturing many household items – including paper, textiles, packaging, adhesives, pharmaceuticals and biodegradable plastics.
In its native state, starch forms insoluble semi-crystalline granules with complex structure and morphology. These granules are composed solely of glucose molecules that are linked together in polymers.
Two distinct polymers occur within starch – amylopectin and amylose.
In all land plants, starch is made within the plastids of plant cells. The Seung lab are interested in the molecular processes that facilitate the formation of starch granules in the plastid.
They discover and study these processes in both model and non-model plants, as well as in major crops. The identification of key components involved in starch synthesis will ultimately lead to novel approaches to improve the cooking, processing and/or nutritional quality of our starch crops.
The groups’ current research has several sub-objectives;
- Understand the mechanism of starch granule initiation. While the biochemistry of how the starch polymers are made is relatively well understood, very little is known about how the formation of a starch granule initiates within the plastid. Also, factors controlling the number of starch granules initiated per plastid are poorly understood. The Seung group have been involved in the discovery and characterisation of several novel proteins that are required for proper granule initiation – including the Protein Targeting to Starch (PTST) family proteins. This work has led to exciting progress in developing a mechanistic understanding of granule initiation in both Arabidopsis leaves and cereal endosperm
- Identify genes that underpin diversity in starch granule morphology and composition. Starch granules come in all different shapes and sizes depending on botanical origin. There is also substantial variation in the ratio of amylopectin and amylose in starch. However, many questions about starch granule assembly and morphogenesis remain unanswered: How do the starch polymers assemble to form the semi-crystalline starch granule – is it self-assembly, or do specific proteins catalyse the process? How is granule growth directed to form different shapes – such as spheres, discs, or ovoids? What are the key determinants of granule size? What determines how much amylose is made into the granule, relative to the amount of amylopectin? The group have been investigating natural variation in starch granule shape, size and composition in order to identify key genetic differences that underpin the diversity
- Develop novel approaches to improve the quality of starch crops. Starch granule size, shape and polymer composition are all known to affect the physico-chemical behaviour of starch during cooking and processing. As they identify new components involved in starch synthesis, they are examining how they can be used to modify starch properties in the plant to improve quality for different end uses. Their particular focus is on wheat starch, which is of enormous economic, social and cultural importance