Resurrecting the Ancient Glow

The color of firefly bioluminescence is primarily determined by the structure of the enzyme luciferase. To date, firefly luciferase genes have been isolated from over 30 extant species producing light ranging in color from deep-green to orange-yellow. We have reconstructed seven ancestral firefly luciferase genes, and characterised the enzymatic properties and crystal structures of the recombinant proteins in order to predict the evolution of firefly light emission. Results showed that the synthetic luciferase for the last common firefly ancestor exhibited blue-shifted emission achieving bright green light caused by a spatial constraint on luciferin molecule in the enzyme, while the fatty acyl-CoA synthetic activity, an original function of firefly luciferase, was diminished in exchange. All known firefly species are bioluminescent in the larval stages, with a common ancestor arising approximately 100 Mya. Combined, our findings propose that within the mid-Cretaceous forest the common ancestor of contemporary fireflies evolved green light luciferase via trade-off of original function, most likely for aposematic display from nocturnal predation.