Meeting Abstract
31.3 Sunday, Jan. 5 08:30 Origin of luciferase genes in cypridinid ostracods (Crustacea) by gene duplication OAKLEY, TH*; LEUNG, N; TORRES, E; Univ. of California, Santa Barbara; Univ. of California, Santa Barbara; Univ. of California, Santa Barbara oakley@lifesci.ucsb.edu
How new traits originate is a central question in evolutionary biology, but the molecular changes that lead to evolutionary novelty are often difficult to determine. We aim to identify the molecular changes that gave rise to bioluminescence in cypridinid ostracods, which use bioluminescence for anti-predator displays and mating signals. Cypridinid bioluminescence occurs when luciferase proteins are secreted from the “upper lip”, a glandular structure above the mouth also involved in digestion. To date, only two luciferases are described from cypridinid ostracods, even though bioluminescence is present in approximately 100 species in the family. We obtained sequences similar to known luciferases from Illumina transcriptomes of multiple luminescent and non-luminescent cypridinid species. We also found genes similar to luciferase that lack secretion signals and therefore could not function in the behavior. We confirmed luciferase function of a multiple genes by expressing the proteins in cell culture and performing light reaction assays. We hypothesize that cypridinid luciferase originated by duplication of vWF-D-domain containing digestive proteins secreted from the upper lip of non-luminescent ostracods. We characterized the efficiency of light reactions for three different paralogs that we call luciferase 1, luciferase 2 and protoluciferase. We see a step wise increase in enzyme efficiency from no activity in protoluciferase to highest activity in luciferase 1. Most of the protein is under purifying selection, but two sites show a pattern consistent with diversifying selection. We also report differences in enzyme kinetics in the luciferase proteins of species that differ in bioluminescence behavior. We pose the hypothesis that enzyme kinetics could be related to bioluminescence behavior.
