Enzymatic promiscuity and the evolution of bioluminescence.

Bioluminescence occurs when an enzyme, known as a luciferase, oxidizes a small-molecule substrate, known as a luciferin. Nature has evolved multiple distinct luciferases and luciferins independently, all of which accomplish the impressive feat of light emission. One of the best-known examples of bioluminescence is exhibited by fireflies, a class of beetles that use d-luciferin as their substrate. The evolution of bioluminescence in beetles is thought to have emerged from ancestral fatty acyl-CoA synthetase (ACS) enzymes present in all insects. This theory is supported by multiple lines of evidence: Beetle luciferases share high sequence identity with these enzymes, often retain ACS activity, and some ACS enzymes from nonluminous insects can catalyze bioluminescence from synthetic d-luciferin analogues. Recent sequencing of firefly genomes and transcriptomes further illuminates how the duplication of ACS enzymes and subsequent diversification drove the evolution of bioluminescence. These genetic analyses have also uncovered candidate enzymes that may participate in luciferin metabolism. With the publication of the genomes and transcriptomes of fireflies and related insects, we are now better positioned to dissect and learn from the evolution of bioluminescence in beetles.