A group of cell biologists at the University of California, Riverside led by Dr. Meng Chen has identified that the protein called phytochrome B which can sense light and temperature, also triggers plant growth and controls flowering time. In a paper published in Nature Communications, the research group reveals that phytochrome B molecule has unexpected dynamics activated by temperature, and behaves differently depending on the temperature and type of light.
Phytochromes switch between active and inactive forms like a binary switch controlled by light and temperature. In open fields where there is direct sunlight, phytochromes switch "on" and absorb far-red light. This active form inhibits stem elongation, limiting the height of plants in direct sunlight. In shaded areas, phytochromes are less active. This "off" form releases the inhibition of stem growth, so plants grow taller in shade to compete with other plants for more sunlight.
Within the cell, light causes "on" phytochromes to combine into units called photobodies inside the cell nucleus. When phytochrome B is off, it resides outside the cell nucleus. It moves inside the nucleus when "on" and changes the expression of genes and growth patterns. Chen's group examined the behavior of cells exposed to different temperature and light conditions from the leaves and stems of Arabidopsis thaliana. The goal was to monitor how photobodies change in response to temperature. The group found that increases in temperature did not cause all photobodies to disappear at once. Instead, specific photobodies disappeared in specific ranges of temperature. Increasing the temperature incrementally reduced the number of photobodies as they disappeared selectively. The mechanism that makes the photobodies disappear selectively must be different from the mechanism that makes them disappear in shade. This suggests individual photobodies could be sensors for specific temperature ranges.