Tohoku University discovers plant temperature sensor molecule: The Rain Tree folds its leaves in the rain

A research group led by Professor Minoru Ueda and Graduate Student Yuki Muraoka of the Graduate School of Science at Tohoku University announced that they have clarified the identity of temperature-sensitive ion channels in plants. Focusing on the phenomenon of the legume tree Samanea saman (also known as the Rain Tree), which folds its leaves when it rains, the researchers found that a decrease in leaf temperature triggers the folding movement. Aside from the temperature effect on leaf folding, the research group also found that the ion channel SPORK2, which is present in cells at the base of the leaf, functions as a sensor molecule to detect temperature changes. These findings are expected to lead to the elucidation of the temperature-sensing mechanism in plants and were published in the November 28 issue of the journal Current Biology.

Temperature sensing is an essential function of all living organisms. Animals, including humans, use so-called transient receptor potential (TRP) channel molecules to sense temperature. These channel molecules are ion channel proteins that transport ions across cell membranes. They also act as temperature-sensing molecules because their function changes in response to temperature variation. By contrast, plants do not have temperature-sensing molecules such as TRP channels. Therefore, the mechanism by which plants sense temperature has been a mystery.

In this study, the research group focused attention on the fact that S. saman, which performs nyctinasty by folding its leaves at night and opening them in the morning, also folds its leaves when it rains. According to another report in 2018, nyctinasty in S. saman is regulated by SPORK2, an ion channel found in cells at the base of the leaf. This time, the research group found that this leaf folding is also triggered by temperature changes. They also found that SPORK2, like the TRP channel, changes its ion transport activity in response to temperature. Genes similar to SPORK2 (orthologs: genes derived from a common ancestral gene through species divergence) are found in other plants aside from S. saman.

Ion channels are proteins that form holes in the cell membrane through which ions are allowed to pass. The TRP channel creates holes for sodium and calcium ions, whereas SPORK2 generates holes for potassium ions. The activities of SPORK2 orthologs in Arabidopsis thaliana were also examined and they were found to be temperature-sensitive ion channels.

Crop production has been severely affected by climate change. Shedding light on the mechanisms by which plants adapt to temperature changes is an urgent issue for stable food production. Professor Ueda said, "When I was in Hawaii for an international conference, I saw the leaves of Samanea saman folding in the rain, and I found it very strange. I had been researching nyctinasty for a long time, and it was thanks to the persistent experiments of my student in charge, Muraoka, that I came to this 'detour' discovery. It will be interesting to see how changes in ion homeostasis due to temperature variations affect plant responses other than leaf movement."

Journal Information
Publication: Current Biology
Title: An outward-rectifying plant K⁺ channel SPORK2 exhibits temperature-sensitive ion transport activity
DOI: 10.1016/j.cub.2023.10.057