Plants allocate sugars produced by photosynthesis from sites of net production (Source) to sites of net consumption or storage (Sink). Crop plants like potato (Solanum tuberosum) or cassava (Manihot esculenta) usually maintain a steep source to sink gradient of sugars to efficiently feed their starch storing sinks. Together with potato, cassava is the 4th most produced starch crop worldwide and represents an important source of income for smallholder farmers in Sub Saharan Africa, where cassava ranks number one in starch crop production. As part of the Bill and Melinda Gates Foundation-funded project CASS, we are exploring molecular and biochemical factors influencing source-sink relationships of cassava organs. Being part of a multinational research endeavor, we ultimately aim to improve source-sink interaction in Cassava and to increase yield and starch quality of cassava tubers. Accordingly, special emphasis is given to study and optimize mechanisms and elements involved in transfer of sugars from leaves into roots in the phase of starch accumulation. Such transfer of sugars requires the efficient movement of these molecules on short and long distance transport pathways, e.g. across single membranes or by mass flow within the phloem system. This transport is catalyzed by various types of sugar carrier pro­teins and corresponding activities, the mode of transport and the source of energy required to move sugars can be studied in various systems such as recombinant yeast cells or selected Arabidopsis mutants.

Fernie AR, Bachem CWB, Helariutta Y, Neuhaus HE, Prat S, Ruan Y-L, Stitt M, Sweetlove LJ, Tegeder M, Wahl V, Sonnewald S, Sonnewald U (2020) Synchronisation of developmental, molecular and metabolic aspects of source-sink interactions. Nat. Plants. 6, 55-66 doi: 10.1038/s41477-020-0590-x

Obata T, Klemens P, Rosado de Sousa L, Schlereth A, Gisel A, Stavolone L, Zeier W, Morales N, Mueller L, Zeeman S, Ludewig F, Stitt M, Sonnewald U, Neuhaus HE, Fernie A (2020) Metabolic profiles of six African cultivars of cassava (Manihot esculenta Crantz) highlight bottlenecks of root yield. Plant J. 102, 1202-1219 doi: 10.1111/tpj.14693