Group Uwe Sonnewald


Plant-Biochemistry and Biotechnology

The research group plant biochemistry and biotechnology concentrates on application-oriented basic science in the field of plant growth and development. In addition aspects of Synthetic Biology are considered. Research interests fall into the following areas:

1. Interaction between plants and the enviroment

According to independent climate models, global temperature will increase and distribution of annual rain falls will change. However, little is known about plant responses to combined heat and drought stress. In case of potato a moderate rise in temperature has already profound effects. Potato is the third most important food crop in the world after rice and wheat. Because of its widely distributed cultivation and high yields, it is considered a critical species in terms of food security in face of a growing world population. However, potato is particularly vulnerable to high temperature during various stages of its life cycle. Elevated temperatures strongly suppress tuberisation, negatively affect storage and shelf life of tubers and reduce fitness of seed potatoes. Breeding new heat-stress tolerant cultivars is an urgent need for sustainable increases in potato production, given the negative impact of the rises in temperature due to global warming.

To unravel the molecular background of the temperature-dependent decline in potato yield, different potato varieties are tested within the interational resarch consortium   HotSol   under field and controlled conditions. This allows a comparison between varieties and identification of mechanisms which are causally linked to heat-tolerance. According to current data, elevated temperatures cause a reduction in the expression of the tuber-inducing FT-signal. Reduced FT expression causes adelayed tuberization and hence reduced tuber yields. Ongoing work aims at better understanding the heat-induced suppression of FT expression. In this respect we also studying metabolic signals (i.e. trehalose-6-phosphate) which might be involved in the fine tuning of plant responses to environmental and developmental signals.

The impact of drought and combined drought and heat stress on barley plants is studied in   BAYKLIMAFIT . Utilizing genetic resources and state of the art omics-technologies the project aims at improving the yield stability of barley under changing environmental conditions. Heat and drought combinations are studied since both cause opposing physiological responses which are likely to lead to a clash of defense reactions. Heat naturally results in the opening of stomata to increase transpiration and hence to cool the leaf surface. On the contrary, drought results in stomata closure. In this context, guard cells, controlling water and gas exchange, as well as antioxidative defense systems play important roles.

Mechanisms underlying plant responses to combinatory stresses are studied. In this context we aim at identifying cellular processes which are linked to stress-tolerance in barley plants. To this end we utilize genetic resources and collaborat we barely breeders.

Consequences of combined biotic and abiotic stresses are studied using the model plant Arabidopsis thaliana. Here we could demonstrate that susceptibility to viral infections is significantly altered by additional abiotic stress applications. Plants exposed to heat and drought are significantly more susceptible to virus infections. Molecular analysis revealed that stress combinations lead to significantly altered signal transduction pathways, which may explain the increased susceptibility. Ongoing work aims at identifying the molecular details of this reprogramming.

2. Manipulation of source-sink relations in crop plants

Distribution of photoassimilates, mainly fixed during photosynthesis in source leaves, to harvestable plant organs is the most important determinant of crop yield. Allocation of photoassimilates is effected by environmental and endogenous factors. In several crop plants temperature and day length significantly determine the switch between vegetative and generative growth. In potato for instance, elevated temperatures promote shoot growth and at the same time inhibits tuber-induction, leading to a reduced tuber yield. Similarly, biotic stress often alters source-to-sink relations to support growth of the invading pathogen. This is achieved by reprogramming primary carbon metabolism and leads to a reduced photoassimilate supply of developing sink tissues. Source-to-sink interactions are not static but change during development. In young growing plants the rate of photosynthesis often exceeds sink demand. Thus photoassimilates accumulate in leaves and reduce photosynthetic efficiency (sink inhibition of photosynthesis). After flowering or induction of vegetative sink tissues (such as roots or tubers), this relation shifts and photoassimilate supply to developing sink tissues can get limiting (source limitation). Over the last decades, many factors influencing source-to-sink relations have been deciphered and this knowledge has been used to design transgenic plants with improved biomass production and yield.

In frame of the project   Metabolic engineering of carbon pathways to enhance yield of root and tuber crops   we try to specifically alter the interaction between leaves and storage roots of cassava plants to increase cassava yield. Here we simultaneously improve leaf (Source) and root (Sink) metabolism.

3. Reprogramming of host metabolism by viral effector proteins

The role of viral effectors in reprogramming plant metabolism is studied in frame of the   CRC796 . The CRC796 elucidates host-pathogen interactions at the molecular and cellular level in order to gain insight into microbial strategies to hijack or reprogram cellular processes of the host. Cellular functions are not static, but dynamic and respond to developmental and environmental stimuli. Responsiveness of cells is mediated by higher order protein networks which associate and dissociate based on dynamic changes in protein composition and/or conformation. These processes are modulated by alterations in gene expression, ligand interactions and post-translational protein modifications resulting in either modified protein functions, altered compartmentation or controlled degradation of proteins. Successful infection by viral or bacterial pathogens requires host recognition and (in many cases) entry into host cells, suppression of host defense, reprogramming of cellular processes, efficient multiplication and systemic spreading of the invader. These processes require specific interactions between microbial effectors and host target structures. Pathogens have evolved numerous strategies to interfere with the host surveillance and defense systems by manipulating protein expression, protein interactions and turnover. Despite the obvious importance of these interactions and the dynamic changes induced by effector proteins, many targets and cellular functions of these effectors are still vaguely known. Therefore, research of CRC796 has focused on the structural basis of effector-host target interactions and on the elucidation of cellular functions of known effector proteins, such as the movement of organelles, endo-membrane trafficking, signal transduction, programmed cell death or nuclear processes. As an example, this revealed insight into the structural basis of the HCMV core nuclear egress pUL50/pUL53 complex, opening new avenues for the development of novel therapeutic strategies using small molecular weight inhibitors to block the nuclear exit of HCMV and hence potentially stop viral replication. Based on the results of the previous funding periods, we will keep analyzing so far unrecognized protein-protein interactions and posttranslational modifications initiated or suppressed by microbial effector proteins. In addition we will focus on strategies to develop and test small molecules interfering with established protein-protein interactions. This will be enabled by designing and using synthetic peptides as protein binding site mimics and by X-ray crystallography-based fragment screening to identify novel binding sites as potential drug targets.

Successful invasion of plants by viruses depends on compatible interactions between host and virus-encoded factors to facilitate genome replication, cell-to-cell movement via plasmodesmata (PD) and long distance transport through the vascular system. In the third funding period we would like to further our understanding of the intracellular trafficking of potato leafroll virus (PLRV) movement protein 17 (MP17) and to unravel the role of molecular chaperones during viral infections. Studying the targeting of human PML in plant cells we observed that nucleolar targeting of hPML in plants is strictly dependent on SUMOylation. Inspired by these experiments we are planning to extend the analysis and study SUMOylation of hPML and plant endogenous nucleolar proteins. With this analysis we contribute to a comparative analysis of the role of SUMOylation for nucleolar proteins in plant and mammal cells.

4. Synthetic Biology

Living cells are capable of performing a myriad of complex processes at the nano-scale. Biologists have made enormous progress in understanding these processes over the past decades by using approaches known from structural biology, cell biology, biochemistry and genetics. Tremendous advances in DNA sequencing, DNA synthesis, bioanalytics and bioinformatics lead to the establishment of a new research field, Synthetic Biology (SynBio). SynBio aims at reconstituting biological phenomena in minimal and controllable systems that allow for the direct manipulation and study of the key-players of interest. In this spirit, a major task in SynBio is the engineering of living systems or developing artificial non-living systems with a protocell as the most minimal unit.

With these new technologies at hand, it is envisaged that artificial cells will be designed on the drawing-board. The development of minimal cells benefits significantly from synthetic genomics and the in silico and experimental determination of the minimal core genome encoding all essential cellular functions. Such cells may be able to produce pharmaceuticals that are extremely challenging to synthesize by conventional means. However, cellular metabolism is complex and far from being completely understood. Therefore, substantial efforts are undertaken to design sub-cellular, partial systems able to perform biological reactions in non-living systems. These systems might significantly expand the repertoire of recombinant pharmaceuticals already produced biotechnologically by designing complex artificial synthesis pathways. The invention of multi-compartmentalized nanoparticles might allow the combination of enzymatic reactions requiring incompatible chemical environments and might therefore boost further applications of artificial cells. These complex nano-devices require metabolite transport across several artificial membranes, which can be possibly controlled by application of switchable pore-forming proteins. Engineered bio-inspired nano-devices may not only serve as nano-factories but may also help to detect and respond to changes in the state of health within the human body. Such autonomous molecular devices could combat diseases at a very early stage in development and might also be used for tissue repair and cell regeneration.

In frame of the   EFI-SynBio   project we try to design novel metabolic modules, construct micro reactor systems and develop bio-inspired LEDs. In recent years, white light-emitting diodes (WLEDs) have become interesting lighting source to replace energy inefficient incandescent light bulbs and environmentally not friendly fluorescent lamps. Production of WLEDs requires phosphors of rare earth elements as down-converting materials. In the EFI-SynBio consortium, we have estabilshed a novel approach to obtain white bio-HLEDs combining UV- and blue-LEDs with a novel coating system using blue, green, and red fluorescent protein based rubber materials.

Many applications require optimized proteins and in some cases structured protein arrangements. These arrangements require protein-protein interaction. Covalent and non-covalent linkages between and within polypetides are highly relevant to control protein activity, stability and helps to organize metabolic flux or signal transduction pathways. Non-covalent crosslinks are mainly stabilized by hydrophobic and ionic interactions as well as hydrogen bonds between specific protein interaction domains. Covalent crosslinks described so far are based on reversible disulfide bonds between two cysteine residues or irreversible isopeptide bonds between a Lys -amino group and a main chain -carboxy group of another amino acid. In this context we try to further develop covalent protein linkages enabling sequence specific isopeptide bonding.

5. Hypoallergenic food by genome editing

Approaches to improve food quality by reducing the allergenic potential plant-derived food are followed in the DFG funded project "Multi-target silencing, genome editing and epitope mapping of tomato allergens". Over the years a number of food allergens could be characterized at the molecular level. This enables breeding strategies to design hypoallergenic food. In a collaborative project we aim at reducing minor and major allergens in tomato fruits. This is achieved by RNAi, amiRNA and genome editing. Since many food allergens play an essential role in plant cells, a strategy was developed to substitute essential allergenic proteins by non-allergenic variants.