Plant-Biochemistry and Biotechnology – Group Uwe Sonnewald

The working group is concerned with application-oriented basic research in the areas of plant growth and development as well as aspects of synthetic biology. Plant growth is regulated by internal and external factors, and anticipated climate changes pose a major challenge for agriculture. In this context, we investigate the molecular basis of plant adaptation to periods of heat and drought in order to make them fit for climate change. In order to increase the productivity of crops such as potatoes or cassava, we are pursuing a biotechnological approach to improve assimilate production, distribution and utilization. In the field of synthetic biology, we are trying to reprogram plant metabolism through targeted protein-protein interactions so that it is better adapted to future climate conditions. At the heart of this work are intermolecular, break-resistant and specific protein linkages ( doi: 10.1186/s13007-020-00663-9 ; doi: 10.1371/journal.pone.0179740 ).

Adaptation to climate change:

According to independent climate models, a redistribution of annual precipitation and an increase in mean temperature in Germany can be expected within the next few decades. However, little research has been carried out to determine which adaptation mechanisms can protect crops particularly effectively against combined heat and drought stress. Even a moderate increase in atmospheric temperature can have drastic effects on the yield potential of potato plants. In this context, the impact on tuber formation plays a key role (doi.org/10.1146/annurev-arplant-080720-084456 ).

In order to better understand the molecular background of drought- and heat-induced yield losses, different potato genotypes are grown under controlled greenhouse and field conditions in international and national research projects and their yield development under stress is comparatively analyzed. Through the combination of genotyping by sequencing, molecular, biochemical, physiological and agronomic phenotyping, yield-relevant genome regions are predicted and validated. This identifies relevant processes, genes and alleles that can be used for breeding and biotechnological purposes. In addition, specific studies are being carried out on known processes. Current results indicate that elevated temperatures suppress the expression of a tuber-inducing FT signal, which greatly reduces tuber formation ( doi: 10.1111/pce.13366 ). The FT protein known as SP6A (Self-Pruning 6A) belongs to the Phosphatidyl Ethanolamine Binding Proteins (PEBP) which, among other factors, support the assimilate supply of tubers by inhibiting the activity of SWEET proteins ( doi: 10.1016/j.cub.2019.02.018 ). By specifically influencing the expression of SP6A, we are looking for ways to produce potato genotypes that can withstand the expected climate change. Both traditional breeding and biotechnological (genome editing, transgenic plants) methods are being used to achieve this goal. Promising results of transgenic SP6A overproducing potato plants, which are characterized by increased tuber formation, show that this could indeed be successful (doi.org/10.1016/j.jplph.2021.153530). Similar to the analyses on heat tolerance, we are trying to improve the potato’s adaptation to drought stress. To this end, we are pursuing approaches to optimize water loss through transpiration or water uptake by improving root growth. In this context, the combined expression of a guard cell-specific hexokinase and SP6A has produced the first potato plants that can withstand combined drought and heat under greenhouse conditions (doi.org/10.3389/fpls.2020.614534). These promising results provide the basis for further research that will hopefully lead to climate-adapted potato varieties.

Improving source-sink relations in crop plants:

The yield of crop plants is largely determined by the interplay between leaves and storage organs. The leaves convert atmospheric carbon dioxide into organic carbon compounds (a process called photosynthesis), whereby oxygen is produced as a “waste product”. Since mature leaves produce more carbohydrates during the day than they consume at night, they can make the surplus available to other organs. The leaves are referred to as source organs. The excess organic compounds are transported from the leaves via the plant’s vascular system to consuming or storing tissues (sink organs). Once in heterotrophic tissues, the compounds are either used for growth (e.g. roots) or storage (in seeds, tubers, etc.). The more assimilates are used to build up storage substances, the greater the yield. Therefore, the interests of plant breeding are focused on storing as many assimilates as possible in storage organs. Based on an increasing understanding of the processes involved in both leaf metabolism and storage metabolism, a number of biotechnological approaches have been developed that promise to increase crop yields (summarized in doi.org/10.1016/j.molp.2022.11.015). The ratio between total biomass and harvestable biomass is referred to as the harvest index. As part of two international research projects ( www.photoboost.org ; cass-research.org ), we are specifically trying to change the interaction between the leaf and storage root of cassava plants and between the leaf and storage tuber of potato plants so that higher yields can be realized. The focus here is on the simultaneous improvement of both the leaf metabolism (source), the transport (phloem) and the metabolism of the storage roots/tubers (sink). The approaches of the cassava project are summarized in the publication by Sonnewald et al., 2020 ( doi: 10.1111/tpj.14865 ). Higher-level approaches are described in Fernie et al, 2020 ( doi: 10.1038/s41477-020-0590-x ).