Sensing temperature
Plants sense temperature, but whether this is the actual temperature, or a perceived difference in temperature, that’s what the scientists are not sure about. Now a group of Japanese scientists think they have the answer, at least for the liverwort Marchantia polymorpha.
Temperature sensing is important to avoid cold-related damage. For example, moving the chloroplasts away from the light-irradiated area of the cell to suppress photoinhibition. Chloroplast movement is regulated by the blue light photoreceptor kinase called phototropin or phot for short. Phot likes blue light and gets excited when it detects it, moving the chloroplast closer. However, phot does not like the cold so much, then it moves the chloroplasts away from the light.
To find out if phot is directly sensing the temperature or only a difference in temperature, the researchers designed two experiments, one in which they lowered the temperature by a 5°C difference, and another in which they lowered the temperature by 15°C. But there was a catch in the first experiment the absolute temperature was lower than in the second experiment.
Directly sensing the temperature
The researchers noticed for the first experiment that the chloroplasts moved away from the light. In the second experiment, where the temperature difference was bigger, but the lowest temperature was higher than in the first experiment (12°C in the second vs 5°C in the first experiment) the researchers did not see any movement of the chloroplasts. Suggesting that the plants sense the actual temperature.
To confirm that it was indeed phot that was sensing the temperature, the researchers modified phot so that it became cold insensitive, then even at 5°C the chloroplasts stayed in the light. But only by low levels of blue light, when the researchers increased the blue light intensity, then these chloroplasts with modified phot did move out of the light when it got cold.
A little phosphorylation
To find out how phot manages the sensing of the temperature, the researchers looked at a feature that phot uses to regulate its activity, autophosphorylation. This autophosphorylation takes place randomly at one or multiple spots on the protein. The researchers noticed that how lower the temperature, the more phot is phosphorylated.
But the type of autophosphorylation decides if the chloroplasts are actually moving out of the light. Up to a point the phot protein can autophosphorylate itself, but after that it needs a sister phot protein to do the autophosphorylation for it. As if it needs someone else to find an empty spot. It is only at this point that the chloroplasts start moving out of the light.
Showing both that the level of phosphorylation is a measure of the temperature and that the way of phosphorylation an indication if more action is required.
Literature
Noguchi, M., Fukushima, T., Wakasugi, S. et al. Phototropin monitors actual temperature, not temperature difference, to regulate temperature-dependent chloroplast movement via cis–trans autophosphorylation mode switching in Marchantia polymorpha. Planta 263, 55 (2026). https://doi.org/10.1007/s00425-026-04923-1
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