One of the main factors that determine the economic viability of biofuel production is the efficiency of photosynthetic CO2 assimilation into storage and structural products by the plant. Improvements in these areas require a thorough understanding of the metabolic fluxes in plant sinks and of the mechanisms that regulate source-sink interactions. For example, little is known about the molecular switches that partition photosynthate to growth and storage. We also don't understand the mechanisms that control feedback inhibition of photosynthesis by sink demand. When we understand these regulatory networks it should be possible to engineer current crops to allocate more carbon to cellulose, starch or other carbohydrates. We study source-sink interactions during cereal development. The long-term objective is to obtain a comprehensive map of the metabolic and regulatory events controlling photosynthetic capacity and sink strength. One direction will be to identify the set of transcription factors that govern sucrose utilization in source and sink tissues. Candidate transcription factors include the SUSIBA family, identified by us (Sun et al., 2003, 2005, 2007). References Sun, C., Ahlandsberg, S., Palmqvist, S., Ohlsson, H, Borén, M. and Jansson, C. (2003) Plant Cell 15, 2076-2092. Sun, C., Olsson, H., Höglund, A.-S., Mangelsen, E. and Jansson, C. (2005) Plant J. 44, 128-138. Sun, C., Ridderstråle, K., Larsson, L.-G., Jansson, C. (2007) Plant J., in press.