Growth control and stress resistance of plants

Plants constantly adapt to changes in their environment in order to adjust their growth and development and increase their chances of survival. For example, during droughts or in winter, the germination of seeds is prevented; shading by neighboring plants leads to increased elongation growth away from the shading and towards the light; Flowering and fruit development are specifically controlled by recognizing the length of the day.

Hormones play an important role in the adaptation of plant development to external conditions and one class of hormones are the brassinosteroids (BR), which are similar in structure to human and animal steroid hormones. BRs promote cell elongation and control essential development processes, such as root and shoot development, the increase in biomass, the control of flowering time and fruit development and ripening. However, they also play a decisive role in the ability of plants to develop resistance against stress (a process called stress adaptation).

A central goal of our research is to clarify how BRs regulate growth, in particular in terms of adaptation to environmental factors. We also try to understand how BRs act in plants when abiotic stress, triggered by extreme temperatures such as heat and frost, or biotic stress, triggered by fungal and bacterial pathogens, prevails. We elucidate molecular and biochemical mechanisms that make it possible to regulate BR concentrations, investigate factors that control BR signal transduction and study the interaction of BRs with other hormones such as the gibberellins and abscisic acid.

Figure 1: Using molecular genetics and Arabidopsis thaliana as a model system we investigate modes that are utilized to adjust BR homeostasis with a focus on glycosyltranferases and acyltransferases in BR catabolic inactivation. Moreover, we aim to understand signaling events that enable for BR function in growth control and stress responses. In this context, we focus on BR-controlled transcription factors, both atypical and typical bHLH proteins and how they are regulated by and interact with other factors, for an integration of different stimuli into BR-controlled physiological processes. To facilitate BR research and their application in plant production, we develop chemical inhibitors that interfere with BR activity at different steps of the pathway (chemical biology).

In our work we use models such as the thale cress Arabidopsis thaliana, and test whether our findings can be transferred to crops, using the cultivated tomato (Solanum lycopersicum).

Selected publications:

Albertos, P., Duendar, G., Schenk, P., Carrera, A., Cavelius, P., Sieberer, T., & Poppenberger, B. (2022) Transcription factor BES1 interacts with HSFA1 to promote heat stress resistance of plants. EMBO J. 3108664

Ramirez, V. & Poppenberger, B. (2017) MAP Kinase Signaling Turns to ICE. Dev. Cell 43: 545-46

Eremina, M., Unterholzner, S.J., Rozhon, W., Kugler, K.G., Castellanos, M., Ratnajaka, A., Khan, M., May, S., Mayer, K.M.  & Poppenberger, B. (2016) Brassinosteroids contribute to the control of basal and acquired freezing tolerance in plants. Proc. Natl. Acad. Sci. USA 113: E5982-91.

Unterholzner ,S.J., Rozhon, W., Papacek, M., Lange, T., Kugler, K.G., Mayer, K.M., Sieberer, T. & Poppenberger, B. (2015) Brassinosteroids Are Master Regulators of Gibberellin Biosynthesis in Arabidopsis. Plant Cell 27: 2261-72    

Khan, M., Rozhon, W., Unterholzner, S.J., Chen, T., Eremina, M., Wurzinger, B., Bachmair, A., Teige, M., Sieberer, T., Isono, E. & Poppenberger, B. (2014) Interplay between phosphorylation and SUMOylation events determines CESTA protein fate in brassinosteroid signalling. Nature Communic. 5: 4687

Poppenberger, B., Rozhon, W., Khan, M., Husar, S., Adam, G., Luschnig, C., Fujioka, S. & Sieberer, T. (2011) CESTA a positive regulator of brassinosteroid biosynthesis. EMBO J. 30: 1149-61


Improving important traits of the sunflower

The sunflower Helianthus annuus is the second most important oilseed crop in Europe. Sunflower oil is obtained by cold pressing from the achenes, nuts formed in the center of the large composite flower and known as sunflower seeds. It is rich in the polyunsaturated fatty acid linoleic acid (C18: 2) and is very popular as an edible oil. In addition, it also has potential for use in the chemical-technical industry as a replacement for petroleum-based products.

For applications in the technical field, but also for high-quality edible oils, a high content of the monounsaturated fatty acid oleic acid (C18: 1) is desired, since high oleic acid (HO) oils with contents of >85% have high oxidation and heat stability. With an oleic acid content of <50%, sunflower oil does not have an ideal composition and one goal of sunflower breeding is therefore to create new varieties that are rich in oleic acid.

We use methods of molecular biology and analytical chemistry to accelerate classical plant breeding work and create new varieties that are rich in oleic acid. We are also looking for ways to increase the resistance of sunflowers to fungal diseases, with a focus on the pathogen Sclerotinia sclerotiorum, which causes great damage to sunflower and a large variety of other important crops. To this end, we develop laboratory-based screening methods and test the relevance of semi-dwarfism, caused by a lack of activity of brassinosteroids or gibberellins, for resistance against Sclerotinia and other relevant traits.

Figure 2: Phenotyping of semi-dwarf sunflower lines in standardized conditions, next to our institute building. Image courtesy: Veronica Ramirez.

Research with African orphan crops

Our planet hosts a rich treasure of plant species that we can use, be it as food sources, as medicinal plants, as ornamentals or as renewable resources. Around 300,000 plants are edible and could contribute to sustaining the world's population, but we only consume a fraction of them. Three crops, rice, wheat and corn, feed half of the world's population. These cereals provide high yields and satisfy hunger. They are rich in carbohydrates and therefore efficient suppliers of calories. In some countries, however, they are often the only food sources for the poorest, and since some cereals, such as rice, contain hardly any vitamins and minerals, malnutrition and resulting diseases are the consequences.

In order to prevent malnutrition, to increase biodiversity on our fields and to reduce our great dependence on the productivity of the major crops, further plant species must be developed, and in this context fruit and vegetables are of crucial importance. Although they are often of great local importance and are perfectly adapted to regional climatic conditions, they are neglected in research and breeding work because there is a lack of sufficiently large global trade. In order to promote the work with neglected plants from Africa, the 'African Orphan Crops Consortium' was founded, a consortium of universities, industrial partners and NGOs, which decodes the genome of the 101 most important cultivated plant species in Africa, to create essential resources for research and breeding. Some of these crops are known worldwide, such as mango, papaya and avocado. Others are hardly known in Europe, such as leafy vegetables of the genus Crassocephalum, named Ebolo in Nigeria, and this species we are investigating in detail.

Ebolo is rich in minerals, vitamins and essential oils and is used as leafy vegetables and medicinal plants in sub-Saharan Africa, parts of Asia and Australia. The species is still mainly collected from the wild, but efforts are made to promote its domestication. For this purpose, cultivation technology must be established and important traits must be improved. We investigate traits such as toxin formation (phyrrolizidine alkaloids), seed development and germination capacity, as well as abiotic stress resistance, with a focus on the activity of plant hormones in these processes. To this end, we establish ecotype collections, generate mutagenized populations for mutation breeding and mutant screens, and establish other tools of molecular genetics, such as regeneration and transformation techniques.

Figure 3: Crassocephalum crepidioides accumulates the pyrrolizidine alkaloid jacobine in response to nitrogen depletion. The hydroponics system developed and used for nitrogen depletion experiments is shown. For details see Schramm et al., 2021, Frontier in Plant Sciences.