Cyanobacterial origin of plant phytochromes.

Phytochromes are widely distributed photoreceptors with similar domain arrangements. The evolutionary origin of plant and green algal phytochromes is currently under debate. We used different algorithms to generate multiple phylogenetic trees for the N-terminal chromophore module and the C-terminal histidine kinase domains. The evolution of the chromophore module and the histidine kinase (like) regions follows different patterns, indicating several rearrangements between both parts of the protein. Out of 22 trees, 19 revealed a close relationship between cyanobacteria and Archaeplastida, the group encompassing plants and green algae. Opposed to other studies, a cyanobacterial origin of plant phytochromes is strongly supported by our results.