Functional and evolutionary diversification of luciferase genes in Metridia lucens

Bioluminescent organisms have developed extraordinary adaptations to produce light using a luciferin-luciferase reaction, fulfilling various ecological functions such as predator evasion, prey attraction, and intraspecies communication. Although the earliest record in the marine environment dates back some 540 millions of years, the evolutionary origins of this phenomenon are still largely unknown in most species. In Metridinidae copepods light production capability is facilitated by a luciferase gene duplication. This study focuses on characterizing the luciferase genes of Metridia lucens, a copepod widely distributed throughout global oceans, excluding the high Arctic. Despite being the first described species in this genus, the genomic sequences of its luciferase genes remained unknown prior to this investigation. Here, using an integrated approach combining molecular cloning and high-throughput sequencing, we isolated and characterized M. lucensluciferase genes. Our results revealed an unexpectedly high genetic diversity both within and between specimens, consistent with the presence of an extended gene family in this copepod's genome. We identified three distinct luciferase gene lineages, each represented by several copies, expanding our knowledge of marine bioluminescence evolution.