Uwe Sonnewald is head of the division of biochemistry at the Friedrich-Alexander-University Erlangen-Nuremberg (FAU). He leads a research group trying to improve plant yield under optimal and stressful environmental conditions. Molecular genetics, genomics and biochemical methods are used to identify and characterize yield components, primarily for potato and cassava plants. Distribution of photoassimilates, mainly fixed during photosynthesis in source leaves, to harvestable plant organs, such as seeds, tubers or roots, is the most important determinant of crop yield. Allocation of photoassimilates is influenced by environmental and endogenous factors. In several crop plants temperature and day length significantly determine the switch between vegetative and generative growth. In this context the group used genetic and biotechnological approaches to overcome the heat-mediated of tuberization. Overexpression of the tuber-inducing FT homolog SP6A resulted in potato plants able to tuberize under elevated temperatures and achieving higher yields as compared to control plants. Beside this, many factors influencing source-to-sink relations have been deciphered and this knowledge has been used to design transgenic plants with improved biomass allocation. One example is the "push-pull" strategy which allowed the simultaneous stimulation of sucrose synthesis in leaves and the conversion of sucrose into starch in developing sink tubers. Source-to-sink interaction | Potato | Cassava