Growth or immune response? Higher organisms must constantly balance these two priorities. As in humans, hormones regulate this balance in plants as well. Researchers at the Technical University of Munich (TUM) have now discovered a mechanism by which plant steroid hormones can inhibit immune responses and thereby make resources available for growth.
Andreas Heddergott / TUM In brief
- Plant steroid hormones regulate immune responses
- Mechanism crucial for balancing growth and defense
- Potential for disease-resistant crops with fewer yield losses
When plants are exposed to pathogens, they activate their immune system and simultaneously stop their growth. For crop production, this results in lower yields. This interplay is of great importance for the breeding of disease-resistant varieties. "Plant breeders are trying to develop varieties that can effectively ward off pathogens without reducing their yield potential. In doing so, however, they encounter biological limits: an increased immunity often comes at the expense of growth," explains Brigitte Poppenberger, professor for Biotechnology of Horticultural Crops at TUM.
Together with her team, she has now discovered a mechanism that could help push these biological boundaries: plant steroid hormones regulate a molecular switch that controls the immune response.
In healthy plants, steroid hormones inhibit the immune response
When plants are not challenged by pathogens, they repress their immune responses to invest all their resources in growth. Steroid hormones play a role in this process, by keeping immune receptors that are needed to trigger an immune reaction, inactive. They do this via transcription factors-proteins that bind to DNA and influence how genetic information is processed. These factors alter the structure of immune receptors and keep them inactive until they are needed. The plant can then utilize resources to grow.
However, when plants encounter pathogens, functional receptors are required to initiate defense reactions. The steroid hormone-regulated transcription factors are then inactivated, allowing the receptors to assemble correctly. Defense responses are activated, while growth is reduced. The researchers demonstrated this in the model plant Arabidopsis thaliana after infection with a powdery mildew pathogen.
Epigenetics Relevant to Plant Breeding
The researchers were the first to identify this steroid hormone-controlled mechanism. They were particularly surprised by how the transcription factor influences immune receptors: "The transcription factor doesn't simply turn receptor genes on or off," explains Brigitte Poppenberger. "Through an epigenetic mechanism, it influences which receptor variant is produced by altering DNA modifications, thereby regulating the processing of the affected genes."
"If future breeding programs succeed in harnessing this mechanism, high-yielding varieties could become more resilient to pathogens."
Ramirez, V.E. et al., Brassinosteroid-regulated transcription factors confer epigenetic changes that repress plant immunity, Proceedings of the National Academy of Sciences, 123/34 (2026), e2532739123, https://doi.org/10.1073/pnas.2532739123
The professorship for for Biotechnology of horticultural crops is part of the TUM School of Life Sciences and the World Agricultural Systems Center Hans Eisenmann-Forum at TUM .
