Phytochrome-interacting factor from Arabidopsis to liverwort

- PIFs have diverged to regulate various aspects of plant life cycles.
- PIF is conserved from seed plants to liverwort.
- Tomato PIF1a regulates carotenoid synthesis in fruits.
- Liverwort PIF regulates gemma germination and LHCB and POR mRNA expression.
- The phy-PIF regulon emerged early in land plant evolution.

Phytochromes are red and far-red light photoreceptors that regulate the responses of plants to light throughout their life cycles. Phytochromes do this in part by inhibiting the function of a group of basic helix-loop-helix transcription factors called phytochrome-interacting factors (PIFs). Arabidopsis has eight PIFs that function sometimes redundantly and sometimes distinctively depending on their expression patterns and protein stability, as well as on variations in the promoters they target in vivo. PIF-like proteins exist in other seed plants and non-vascular plants where they also regulate light responses. The mechanism by which phytochrome regulates light responses by promoting the degradation of the PIFs is conserved in liverwort, suggesting it must have evolved some time before the last common ancestor shared by seed plants and non-vascular plants.