The plant that doesn’t feel the cold

Scientists at the John Innes Centre in Norwich, UK, have discovered that plants have a built-in thermometer that they use to control their development.

Plants are exposed to huge variations in temperature through the seasons as well as big differences between night and day. To cope with this, they sense the temperature around them, and adjust their growth accordingly. Publishing in the journal Cell, they have now identified a thermometer gene, which could be crucial for breeding crops able to cope with the effects of climate change.

Plants can sense differences of just 1ºC, and climate change has already had significant effects, bringing forward when some plants flower and changing global distributions of species. While the effect of temperature on plants has been known for hundreds of years, it has been a mystery until now how temperature is sensed.

To solve this problem, Vinod Kumar and Phil Wigge at the John Innes Centre, an institute of the Biotechnology and Biological Sciences Research Council (BBSRC), looked at all of the genes in the model plant Arabidopsis to see which are switched on by warmer temperature.  They connected one of these genes to a luminescent gene to create plants that give off light when the temperature is increased. In this way, the team could screen for mutants that could no longer sense the proper temperature. One mutant was particularly interesting, since it lost the ability to sense temperature correctly.  The plant behaved as though it was hot all the time, and the scientists could see this as the plant was luminescent when it was warm and cold.

“It was amazing to see the plants,” said Dr Vinod Kumar, who discovered the mutant plant. “They grew like plants at high temperature even when we turned the temperature right down.”

This plant has a single defect that affects how a special version of a histone protein works. Histone proteins bind to DNA and wrap it around them, and so control which genes are switched on. Remarkably, when this specialised histone is no longer incorporated into DNA, plants express all their genes as if they are at a high temperature, even when it is cold. This told the scientists that this specialised histone is a key regulator of temperature responses.

The histone variant works as a thermometer by binding to the plant’s DNA more tightly at lower temperatures, blocking the gene from being switched on.  As the temperature increases, the histone loses its grip and starts to drop off the DNA, allowing the gene to be switched on.

The temperature sensing histone variant was found to control a gene that has helped some plant species adapt to climate change by rapidly accelerating their flowering.  Species that do not adjust their flowering time are going locally extinct at a high rate. Plants must continually adapt to their environment as they are unable to move around, and understanding how plants use temperature sensing will enable scientists to examine how different species will respond to further increases in global temperatures.

“We may be able to use these genes to change how crops sense temperature,” said Dr Wigge.  “If we can do that then we may be able to breed crops that are resistant to climate change.”