Researchers discover new mechanism for plants to perceive light and heat

Researchers from the University of Bayreuth and the Heinrich Heine University of Düsseldorf have described a previously unknown mechanism in the perception of light and heat in plants. The results contribute to a better understanding of plant physiological processes. The results are published in the journal The plant cell.

Plants can perceive light and heat via so-called phytochromes and use these pigments to trigger vital reactions such as growth. Climate change and ever-rising temperatures can disrupt plant metabolism, slowing growth and potentially leading to the death of plants, including crops.

In this context, an understanding of the molecular basis of the mechanisms that control light and heat perception in plants is essential. The results may also lead to advances in the control of cellular activity by light (optogenetics), in biotechnology and in fundamental research.

Plants must constantly adapt to different environmental conditions, such as different temperature and light conditions throughout the day. These stimuli are perceived at the molecular level via phytochromes, which change state when temperature or wavelength changes. They interact with other proteins such as phytochrome-interacting factors (PIFs), which trigger physiological responses to stimuli, such as growth.

Phytochromes react to red light: in the dark, phytochromes are in the inactive Pr state; when irradiated by red light, they are converted to the active Pfr state. This change of state can be reversed by changing the temperature or by irradiating with far-red light between 710 and 740 nm wavelength. This reaction illustrates the dual function of phytochromes in the perception of heat and light, that is to say as thermoreceptors and photoreceptors.

A central element of the thermoreception of phytochrome B from Thale watercress (Arabidopsis thaliana) is the pronounced temperature dependence of the transition from the Pfr state to the Pr state. This conversion is increased more than tenfold at temperatures between 4 °C and 27°C. However, it was not yet known to what extent the interaction between phytochrome B and different PIFs could contribute to plant thermoreception.

This is where Professor Andreas Möglich and doctoral student Chengwei Yi from the Photobiochemistry working group at the University of Bayreuth come in. Together with researchers from Heinrich Heine University Düsseldorf, they studied the rate of formation and dissolution of phytochrome B complexes and various PIFs under red and far-red light and at different temperatures. The dissolution of complexes accelerated several times between 15°C and 30°C, while this did not apply to the formation of complexes.

By studying the interaction between phytochrome and PIF under red light, the researchers discovered an unexpected effect: under continuous strong light, the extent of complex formation decreased with the intensity of the red light instead of increase as expected. The reason is a rapid, red light-driven bidirectional conversion between the Pr and Pfr states.

“Plant phytochromes can therefore convert different intensities and temperatures of red light into physiological reactions via an additional molecular mechanism, previously unknown and therefore unexplored,” explains Chengwei Yi, first author of the study.

The results help advance the use of plant phytochromes in biotechnology, for example for the precise control of gene activation for protein production. They also impact the perception and integration of light and thermal signals in plants.