Interaction of light and temperature on the phytochrome: PIF signalling complex

Light and temperature are two of the most important non-biological signals that plants must be able to sense and respond to. However, it is not just the individual signals, but the interaction between them that is important. In the dark, Arabidopsis has strongly reduced temperature plasticity. The red light photoreceptor phyB and the PIF family of transcription factors have previously been identified as key regulators of this response. Computer modelling was used to study the interaction between the proteins, to explain counter-intuitive behaviour at certain light conditions. A fluence rate dependent response to temperature was uncovered, where high temperature causes a reversal of the normal seedling response to light. In a PIF and phyB dependent manner, increasing light intensity in the warm can lead to an increase in hypocotyl elongation, the opposite of what has been previously published. This was shown to be dependent on an apically derived response to high fluence rates, independent of the Phytochromes. To extend the analysis beyond the seedling stage, the adult phenotypes of light signalling mutants were subsequently characterised at different temperatures. The temperature dependent control of flowering time and leaf growth were both dependent on Phytochrome and the PIFs, but in apparent opposite directions. This demonstrates that the light signalling system in plants is a complex network of signalling factors, affecting each other in a dynamic process to respond to light and temperature