Marine algae and land plants share conserved phytochrome signaling systems
Résumé
Significance Phytochromes are photosensory signaling proteins widely distributed in unicellular organisms and multicellular land plants. Best known for their global regulatory roles in photomorphogenesis, plant phytochromes are often assumed to have arisen via gene transfer from the cyanobacterial endosymbiont that gave rise to photosynthetic chloroplast organelles. Our analyses support the scenario that phytochromes were acquired prior to diversification of the Archaeplastida, possibly before the endosymbiosis event. We show that plant phytochromes are structurally and functionally related to those discovered in prasinophytes, an ecologically important group of marine green algae. Based on our studies, we propose that these phytochromes share light-mediated signaling mechanisms with those of plants. Phytochromes presumably perform critical acclimative roles for unicellular marine algae living in fluctuating light environments.