Plants can smell, now researchers know how

Plants don't need noses to smell. The ability is in their genes. Researchers at the University of Tokyo have discovered the first steps of how information from odour molecules changes gene expression in plants. Manipulating plants' odor detection systems may lead to new ways of influencing plant behaviour.

The discovery is the first to reveal the molecular basis of odor detection in plants and was more than 18 years in the making.
"We started this project in 2000. Part of the difficulty was designing the new tools to do odor-related research in plants," said Professor Kazushige Touhara of the University of Tokyo.
Plants detect a class of odour molecules known as volatile organic compounds, which are essential for many plant survival strategies, including attracting birds and bees, deterring pests, and reacting to disease in nearby plants. These compounds also give essential oils their distinctive scents.
Touhara's team exposed tobacco cells and 4-week-old tobacco plants to different volatile organic compounds. They discovered that odour molecules change gene expression by binding to other molecules called transcriptional co-repressors that can turn genes on or off.
In plants, the odour molecules must move into the cell and accumulate before they affect plant behaviour. In animals, odour molecules are recognised by receptors on the outside of cells in the nose and immediately trigger a signaling pathway to recognise the odour and change behaviour.
"Plants can't run away, so of course they react to odours more slowly than animals. If plants can prepare for environmental change within the same day, that is probably fast enough for them," said Touhara.
Speed is unnecessary for plants, but they may be able to recognise a much greater variety of odour molecules.
"Humans have about 400 odour receptors. Elephants have about 2,000, the largest number in animals. But based on how many transcription factor genes are in plants, plants may be able to detect many more odours than animals," said Touhara.
Touhara imagines applying these discoveries to influence crop quality or character without the complications of gene editing or pesticide use. Farmers could spray their fields with an odour associated with a desired plant behaviour. For example, an odour that triggers plants to change the taste of their leaves to deter insects.
"All creatures communicate with odour. So far, our lab has studied within-species communication: insect to insect, mouse to mouse, human to human. This understanding of how plants communicate using odor will open up opportunities to study 'olfactory' communication between all creatures," said Touhara.
The University of Tokyo research team made their discoveries using tobacco plants, a common model organism. They expect research teams around the world will soon verify the discovery in many other types of plants.