Shade avoidance in the context of climate change.

When exposed to changes in the light environment caused by neighbouring vegetation, shade-avoiding plants modify their growth and/or developmental patterns to access more sunlight. In Arabidopsis (Arabidopsis thaliana), neighbour cues reduce the activity of the photo-sensory receptors phytochrome B (phyB) and cryptochrome 1 (cry1), releasing photoreceptor repression imposed on PHYTOCHROME INTERACTING FACTORs (PIFs) and leading to transcriptional reprogramming. The phyB-PIF hub is at the core of all shade-avoidance responses, whilst other photo-sensory receptors and transcription factors contribute in a context-specific manner. CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) is a master regulator of this hub, indirectly stabilising PIFs and targeting negative regulators of shade avoidance for degradation. Warm temperatures reduce the activity of phyB, which operates as a temperature sensor, and further increases the activities of PIF4 and PIF7 by independent temperature sensing mechanisms. The signalling network controlling shade avoidance is not buffered against climate change; rather, it integrates information about shade, temperature, salinity, drought, and likely flooding. We therefore predict that climate change will exacerbate shade-induced growth responses in some regions of the planet while limiting the growth potential in others.