Starch synthesis and degradation in storage organs:
We aim to understand how starch granules are synthesised and degraded in the major starch-storing organs of crop plants. Historically, we studied peas carrying mutations that affect starch synthesis in the seed, and transgenic potatoes with reduced activities of specific proteins involved in starch synthesis. Currently, we are working in close collaboration with Kay Denyer on starch synthesis and degradation in cereal seeds, and on starch synthesis in cassava.
Current research in the Smith Lab:
Barley starch degradation
In collaboration with Kay Denyer and Rob Field, we are studying the control of starch degradation in germinating barley seeds. This process is central to the production of malt for beer and whisky manufacture. It is also relevant to understanding pre-harvest sprouting and related problems in cereal crops, and to the production of bioethanol from cereals. A great deal is known about the synthesis and structure of the individual enzymes involved, and many genetic factors that influence the malting process have been identified. Much less is known about how the rate of starch degradation is controlled in vivo during germination. We are taking two approaches:
- Chemical genetics. With Rob Field and colleagues, we are discovering new specific and class inhibitors for the major enzymes believed to be involved in starch degradation, and applying libraries of compounds to germinating seeds to identify novel inhibitors. This research is in collaboration with Birte Svensson, Danish Technical University.
- Reverse genetics. Using RNAI technology, Wendy Harwood and the BRACT transformation service are producing mutant lines of barley with altered amounts or properties of the major enzymes of starch degradation.
Other colleagues involved in this work are John Flintham,Stephen Bornemannand David Lawson.
Barley seeds germinated in the absence (left) and presence (right) of the α-glucosidase inhibitor deoxynojirimycin.
The Smart Carbohydrate Centre:
The Smart Carbohydrate Centre (http://www.monogram.ac.uk/SmartCarb/intro.php) will provide new resources for end-users and breeders of wheat and barley, paving the way for the development of new cultivars with improved or novel food and industrial value, and of new, renewable raw materials for industry.
· With Kay Denyer, and with Andy Greenland at the National Institute of Agricultural Botany, Cambridge, we have set up the Smart Carbohydrate Centre to uncover and exploit novel variation for starch properties in wheat and barley.
· We have already found lines of barley with unusual starches. Discovery of the genes responsible for this variation will provide new, fundamental information about the synthesis of starch in cereal seeds. In addition, flours and starches from these lines are of potential value in baking, brewing, functional foods, industrial and food applications of starch and bioethanol production.
· We will produce systematic information about the functional properties of these starches, and look for further variation in barley and in wheat. We will generate new breeding lines of wheat and barley containing these starches, for bulking up and commercial testing.
· The Smart Carbohydrate Centre depends for its success on a consortium of end-users of barley and wheat. The consortium has access to all of the information and materials generated by the Centre. Members evaluate and test the Centre’s outputs in an iterative fashion. The outcome will be a breeding programme that will introduce novel, valuable functionalities into UK wheat and barley.
New cassava starches:
In collaboration with Kay Denyer, we are helping colleagues at CIAT in Colombia in their efforts to identify new variation for starch properties in cassava. Screens of starch from mutant and inbred populations have already discovered novel variation, including a naturally-occurring waxy (amylose-free) trait.
Left to right: Kay Denyer screening starch samples from a mutant, inbred population of cassava at CIAT; a cassava crop; cassava harvest
Recent relevant publications:
Hussain H., Mant A., Seale R., Zeeman S., Hinchcliffe E., Edwards A., Hylton C., Bornemann S., Smith A.M., Martin C. and Bustos R. (2003) Three isoforms of isoamylase contribute different catalytic activities for the debranching of potato glucans. Plant Cell 15, 133-149
Fulton D.C., Edwards A., Pilling E., Robinson H.L., Fahy B., Seale R., Kato L., Donald A.M., Geigenberger P., Martin C. and Smith A.M. (2002) Role of granule-bound starch synthase in determination of amylopectin structure and starch granule morphology in potato. J. Biol. Chem. 277, 10834-10841
Pilling E. and Smith A.M. (2003) Growth ring formation in the starch granules of potato tubers. Plant Physiol. 132, 365-371
Bustos R., Fahy B., Hylton C.M. Seale R., Nebane N.M., Edwards A., Martin C. and Smith A.M. (2004) Starch granule initiation is controlled by a heteromultimeric isoamylase in potato tubers. Proc. Natl Acad. Sci., 101,2215-22220.
Smith A.M., Zeeman, S.C. and Smith S.M. (2005) Starch degradation. Ann. Rev. Plant Biol. 56, 73-07.
Smith AM, Zeeman SC (2006) Quantification of starch in plant tissues. Nature Protocols 1, 1342-1345
Smith, AM, Stitt M (2007) Coordination of carbon supply and plant growth. Plant Cell Env. 30, 1128-1149.
Ceballos H, Sáchez T, Morante N, Fregene M, Dufour D, Smith AM, Denyer K, Pérez JC, Calle F, Mestres C (2007) Discovery of a waxy starch mutant in cassava. J. Agric. Food Chem. 55, 7469-7476.
Ceballos H, Sánchez T, Tofiño AP, Rosero EA, Denyer K, Smith A, Dufour D, Morante N, Pérez JC, Fahy B, Fregene M (2008) Induction and identification of a small-granule, high-amylose mutant in cassava (Manihot esculenta Crantz). J. Agric. Food Chem. 56, 7215–7222
Smith AM (2008) Prospects for increasing starch and sucrose yields for bioethanol production. Plant J. 54, 546-558.
