New Mechanism Of Plant Immune Defense Discovered

Higher yield and more resilient: TUM researches mechanisms of disease resilience in plants

Growth or disease defense? In higher organisms, scarce resources are constantly being allocated between these two priorities. As in humans, this balance is also regulated by hormones in plants. Researchers at the Technical University of Munich (TUM) have now discovered a mechanism by which plant steroid hormones can inhibit the immune response and thereby free up resources for growth.

Shortly

• Plant steroid hormones regulate the immune system.
• Mechanism important for balance between growth and defense
• Potential for disease-resistant crops with less yield loss

When plants are exposed to pathogens, they activate their immune system and simultaneously halt their development. For plant production, this means lower yields. This interaction is of great importance for breeding disease-resistant varieties. "Plant breeders try to develop varieties that can effectively ward off pathogens without reducing their yield potential. However, they encounter biological limits: increased immune defense often comes at the expense of growth," explains Brigitte Poppenberger, Professor of Biotechnology of Horticultural Crops at TUM.

With her team, she has now discovered a mechanism that could help to push these biological boundaries: plant steroid hormones regulate a molecular switch that controls the immune system.

Steroid hormones inhibit the immune system in healthy plants.
When plants are not exposed to pathogens, they suppress their immune defenses to invest all resources in growth. Steroid hormones play a role in this process by switching off immune receptors that plants need to activate their immune response. They do this using transcription factors, proteins that bind to DNA and determine how the genetic information stored within it is processed. Through these transcription factors, steroid hormones alter the structure of the immune receptors, thereby inactivating them. The plant can then redirect resources to growth.

When plants are infected by pathogens, they need active immune receptors to initiate defense responses. The steroid hormone-regulated transcription factors then become inactive, and relevant immune receptors can develop correctly. This activates the immune system and slows growth. Researchers were able to demonstrate this using the model plant Arabidopsis thaliana (thale cress) when infected with a pathogen that causes powdery mildew.

Epigenetics relevant to breeding
Researchers at TUM have identified for the first time this mechanism, which steroid hormones use to regulate the balance between growth and immune defense. They were particularly surprised by how the transcription factor influences immune receptors: "The transcription factor doesn't simply switch immune receptor genes on or off," explains Brigitte Poppenberger. "Through an epigenetic mechanism, it influences which immune receptor variant is produced by altering the DNA marker, thereby regulating the processing of the affected genes." Thus, under the influence of the transcription factor and ultimately the steroid hormones, the number of active immune receptors is reduced. Plants in which the amount of these transcription factors was reduced showed increased resistance to powdery mildew without any loss of growth.

"If future breeding programs succeed in utilizing this mechanism, high-yielding varieties could be developed that are better prepared for infestation by pathogens and are therefore more resistant."