Molecular Plant Physiology and Crop Biotechnology
Nutzpflanzenbiotechnologie, Getreidebiotechnologie, Zellbiologie/Intrazellulärer Proteintransport und -deposition, Molekulares Farming.
Produktion von rekombinanten Proteinen in Pflanzengeweben mit Schwerpunkt auf Samen, Zellbiologische Untersuchungen von Speichergeweben mit grundlagenwissenschaftlichen Fragestellungen und anwendungsorientierten Zielen, genetische Veränderung von Nutzpflanzen einschliesslich Getreidearten.
Leader: Univ. Prof. Mag. Dr. Eva Stoeger
- Cereal Biotechnology
Our commitment to biotechnological applications comprises two main areas: Nutritional improvement of food and feed crops, and the production of pharmaceutical proteins in cereal grains. In this context we are engaged in programs targeting the molecular manipulation of the micronutrient content and bioavailability. These activities allowed us to generate and study germplasm with significantly increased amounts of bioavailable iron as a result of engineering individual genes, and we are now embarking on a study aiming at increased phosphorous uptake from cereal-based animal feed.
The use of transgenic crops for the production of value added compounds is a popular target of contemporary plant biotechnology. Using crop plants as “bioreactors” is particularly sensible for recombinant pharmaceutical proteins that are normally too expensive to produce through conventional means. This applies mostly to proteins that are required in large amounts for potential use in diagnosis and treatment of serious conditions such as certain cancer types, infectious diseases and allergies. Cereals are convincing candidate production vehicles because they do not contain toxic alkaloids, and because recombinant proteins are very stable in dry cereal seeds facilitating long-term storage and easy distribution prior to processing. We have recently demonstrated that recombinant therapeutic and diagnostic antibodies remain functional in dry transgenic wheat seeds even after storage at room temperature for more than two years. Wheat, maize and rice are particularly suitable because they are among the most important crops, with well-established agricultural and processing practices world-wide.
Over the last 10 years, recombinant protein expression in plants has progressed from proof-of-principle demonstrations to the point where several plant-made pharmaceuticals have already proven successful in clinical trials. Despite these advances, key limitations remain that hamper the transition from laboratory models to useful crop production systems.One constraint is for example the considerable variability in the levels of expression and accumulation that have been reported with different recombinant proteins. It is therefore essential to study the factors involved in recombinant protein accumulation, and to understand how they can be controlled. This can be achieved by understanding in detail the processes that regulate intracellular protein assembly and sorting: the efficiency of such processes correlates directly to the overall yield of biologically active protein. The optimization of protein folding, assembly and deposition is therefore to be envisaged as a key step for maximizing production and for meeting the specific requirements of a recombinant protein for a particular application. One of our main objectives is therefore to create a sound scientific basis to elucidate underlying processes that affect the expression and accumulation of recombinant proteins in the grain.
The study of protein trafficking within the secretory pathway of plant cells is particularly complex in the cereal endosperm because of prominent and functionally distinct types of protein bodies. Unlike dicotyledonous plants, cereals synthesize different classes of storage proteins with different solubility. Prolamines are soluble in dilute alcohol, whereas globulins are salt-soluble. Most globulins are, after initial translocation into the lumen of the endoplasmic reticulum (ER), transported via the Golgi apparatus and utilize targeting information to reach the storage vacuole. Prolamines are synthesized on the ER but their transportation and deposition as protein bodies differ between cereal species. In maize and rice, prolamines remain within the ER and aggregate into protein bodies by direct enlargement of the ER. In wheat, the situation is less clear with observations indicating either a similar direct deposition in the ER, transport to the protein bodies via the Golgi apparatus, or a combination of both routes. Gliadins appear to follow the standard secretory pathway, via the Golgi to the vacuole, whereas glutenins appear to accumulate directly within the lumen of the ER. Over the last years, we have gathered information on the expression and targeting of immunoglobulins and other mammalian and plant proteins in different plant species, including cereals. Interestingly, we found that different recombinant proteins that are controlled by the same regulatory and targeting sequences behave differently according to tissue and plant type. We are now investigating the mechanisms that determine the fate of these recombinant molecules in the endosperm of cereals. Seeds are attractive targets for a number of molecular farming applications, and therefore these results will help us to define methods for optimising the yield and ease of purification of complex multimeric proteins in transgenic crop plants, including cereals, such as rice, maize and wheat.
Scanning Electron Microscopy (SEM)