Image: A. Heddergott / TUM
As a result of a changing climate, the past few decades have seen increased incidences of heat waves with record highs around the globe. In fact, July 2021 was the hottest month ever documented on the planet. In the U.S., the mean temperature was higher than the average for July by 2.6 degrees Fahrenheit, and many southern European countries saw temperatures above 113º including an all-time high temperature of 120º recorded on the eastern coast of Sicily in Italy.
These heat waves are occurring more frequently, are hotter, and have been lasting longer, with severe consequences not only for humans and animals but also for plants. “Heat stress can negatively affect plants in their natural habitats and destabilize ecosystems while also drastically reducing crop harvests, thereby threatening our food security,” says Brigitte Poppenberger, Professor for Biotechnology of Horticultural Crops.
But they do have a way to increase their chances of survival. They activate the “heat shock response,” a molecular pathway like the one used by human and animal cells for stress protection. Now, thanks to work by researchers at the Technical University of Munich (TUM), we’ve learned they have additional tools to protect themselves. Internally produced plant steroid hormones can increase the heat shock response in plants and improve their chances of survival.
Cells activate a molecular defense pathway for heat stress protection
Here’s what we know.
To survive short periods of heat stress, plants activate a molecular pathway called the heat-shock response. This heat-shock response (common to all organisms) protects cells from damage inflicted by proteotoxic stress, which damages proteins. Such stress is not only caused by heat but can also result from exposure to certain toxins, UV light, or soil salinity.
The heat shock response protects cells in various ways, one of them being production of so-called heat-shock proteins, which serve as molecular shields that protect proteins by preventing misfolding.
Brassinosteroids can increase the heat stress resistance of plants
Plants respond to heat stress by activating heat shock factors and other molecular players, including hormones as chemical messengers. Among the hormones that plants produce are the brassinosteroids, which primarily regulate plant growth and development. More importantly for heat-stressed plants, brassinosteroids can increase the heat stress resistance of plants, and researchers at TUM have recently discovered what contributes to this protective ability.
Using the model plant Arabidopsis thaliana, a research group led by Prof. Brigitte Poppenberger has been able to explain how a special protein responsible for switching certain sections of the DNA on or off is regulated by brassinosteroids. This protein, BES1, can interact with heat shock factors to allow genetic information to be targeted towards increased production of heat shock proteins.
When BES1 activity is increased, plants become more resistant to heat stress, and when it is decreased, they become more sensitive to it. Dr. Poppenberger and her group also found that BES1 is activated by heat stress and that this activation is stimulated by brassinosteroids.
Why Do We Care?
“These results are not only of interest to biologists trying to expand our understanding of the heat shock response but also have potential for practical application in agriculture and horticulture,” says Prof. Poppenberger.
Bio-stimulants containing brassinosteroids are available and can be tested for their ability to increase heat stress resistance in plants. Such substances are natural products that are approved for organic farming and thus could be used without problems. Alternatively, BES1 may be an interesting target for breeding approaches. This could be used to create crop and forage varieties that are more resistant to heat stress and thus provide more stable yields in the event of future heat waves.
