Paths through the phytochrome network.

Since the discovery of the physical interaction between phytochrome B and the basic helix-loop-helix (bHLH) transcription factor (TF) PIF3 a decade ago, plant phytochrome-signalling research has largely focused on understanding the mechanisms through which phytochromes and members of this bHLH family signal. This concerted effort has revealed how phytochrome and bHLH TF control gene expression and plant growth, and has assigned precise roles to a number of genes in the PIF3-like bHLH TF clade. This work has focused largely on cell autonomous signalling events; however, to synchronize plant growth and developmental events at the tissue and organ level, temporal and spatial signal integration is crucial. This review brings together current knowledge of phytochrome signalling through phytochrome-interacting factors (PIFs)/phytochrome-interacting factor-like (PILs), and it evaluates the current evidence for cross-tissue signal integration.