Butterfly wing iridescence is regulated byaraucan, a direct target of optix and spalt

Abstract

ABSTRACTButterfly wings are notable for the diversity of structural colors they display, including many striking hues of iridescence. Little is known, however, about how iridescent coloration is genetically determined. Here we show that theIroquois-complex transcription factoraraucanhas a highly specific effect on wing scale iridescence hue in the common buckeye butterfly,Junonia coenia. CRISPR knockouts ofaraucancause dorsal wing scales to shift from gold to blue iridescence, and eyespot focus scales to shift from purple iridescence to colorless. These effects are associated with a change in thickness in the scale cell basal lamina, as also seen in knockouts of the color pattern transcription factoroptix. We further show that optix and the eyespot transcription factor spalt both bind to the promoter ofaraucan, suggesting that these two factors directly regulatearaucan.Together, our data lead us to propose thataraucanplays a specialized role in determining the hue ofJ. coeniawing scale iridescence and is directly regulated by core wing patterning transcription factors to modulate structural coloration.