Plant roots grow longer when the soil is not only slightly warmer but also a bit drier. Researchers at Wageningen University & Research (WUR) have discovered that these two environmental factors work together to boost growth, with main roots growing up to 30 percent faster.
Their findings were recently published in the scientific journal Current Biology.
© Elizabeth van Veen
Plant roots grow longer when the soil is not only slightly warmer but also slightly drier
Synergy between heat and drought
In soil-based growth experiments, researchers exposed the roots of the model plant Arabidopsis thaliana, commonly known as thale cress, to a temperature of 28°C instead of the usual 20°C. At the same time, the plants received slightly less water, inducing mild drought stress. This combination led to a significant increase in root length, demonstrating that soil temperature and moisture levels work together to stimulate root growth.
This growth response to heat, known as thermomorphogenesis, has already been widely studied in stems and leaves. However, much less was known about how plant roots respond to changes in soil temperature and moisture.
This study shows that roots operate with their own signaling network, allowing them to independently adjust their growth to suit the conditions underground.
Advantage of longer roots
Longer roots help plants absorb water and nutrients more effectively, especially under stressful conditions like heat and drought. By growing deeper into the soil, plants can reach more humid layers below the surface, improving their chances of survival when the upper soil dries out.
The researchers identified three key proteins involved in regulating this combined growth response:
SnRK2.2 and SnRK2.3
These proteins, known as kinases, are essential for the enhanced root growth that occurs under both heat and drought stress. Without them, the growth boost simply doesn't happen.
COP1
This protein acts as a suppressor. It inhibits the enhanced root growth when there's no drought stress present.
HY5 in Trichoblasts
HY5 is a transcription factor that determines which genes are turned on or off in root hair cells (trichoblasts). SnRK2.2 and SnRK2.3 increase HY5 stability, while COP1 reduces it. The more stable HY5 is, the more vigorous the root elongation becomes.
© WUR; Hayes, Leong et al., Current Biology, CC-BY Open Access publication
Synergy between heat (28°C) and mild drought stress stimulates root growth in Arabidopsis via the kinases SnRK2.2/2.3, the E3-ligase COP1, and the transcription factor HY5
Valuable knowledge for breeders
Climate change is causing greater fluctuations in soil temperature and increasingly irregular rainfall, making growing conditions less predictable for crops. This research sheds light on the specific molecules that control root growth under both heat and mild drought stress.
Plant breeders can use this knowledge to develop crop varieties with stronger, more resilient root systems. At the same time, growers can fine-tune their cultivation strategies to better respond to shifting soil temperatures and moisture levels.
According to the researchers, these insights could lead to more stable harvests and more efficient water use in the future.
Research on climate-resistant plants continues at WUR, including in the growth fund program CropXR.
For more information:
Wageningen University & Research 
https://www.wur.nl/
