Knockdowns of red Malphigian tubules reveal pigmentation roles in the milkweed bug

Classical Drosophila eye color mutations have unearthed a toolkit of genes that have permitted candidate gene studies of the outstanding diversity of coloration patterns in other insects. The gene underlying the eye color phenotypes of the red Malphigian tubules (red) fly mutant was mapped to a LysM domain gene of unknown molecular function. Here, we used RNAi to test the role of a red ortholog in the pigmentation of the milkweed bug Oncopeltus fasciatus, and contrast its effect with the ommochrome biosynthetic pathway gene vermilion (ver). Pigmentation was reduced in the cuticle of embryonic legs and first instar abdomens following parental RNAi against red, but not against ver, likely reflecting an effect on pterin biogenesis. Nymphal RNAi of red and ver both resulted in adult eye depigmentation, consistent with an effect on ommochrome content. These results suggest red loss-of-function impacts biochemically distinct types of pigments, and we discuss its putative role in the biogenesis of lysosome-related organelles such as ommochromasomes and pterinosomes.