Three Melanin Pathway Genes, TH, yellow, and aaNAT, Regulate Pigmentation in the Twin-Spotted Assassin Bug, Platymeris biguttatus (Linnaeus)

Abstract

Pigmentation plays a vital role in insect survival and reproduction. Many melanin pathway genes have been studied in holometabolous insects; however, they have only been studied in two hemimetabolous insect genera, <i>Oncopeltus</i> and <i>Periplaneta</i>. Here we analyzed three melanin pathway genes (<i>TH</i>, <i>yellow</i>, and <i>aaNAT</i>) using RNA interference (RNAi) in another hemimetabolous insect, namely the twin-spotted assassin bug, <i>Platymeris biguttatus</i>. <i>TH</i> was highly expressed in freshly molted nymphs and adults. <i>TH</i> RNAi resulted in a complete loss of black pigment, with yellow coloration maintained. Therefore, black pigment in this assassin bug is solely generated from the melanin pathway, whereas yellow pigment is generated from other unknown pigmentation pathways. <i>yellow</i> and <i>aaNAT</i> were highly expressed in the white spot of the hemelytra. Downregulation of <i>yellow</i> caused a brown phenotype with high mortality, indicating an important role of <i>yellow</i> functions in cuticle formation and in the process of converting melanin from brown to black. Interestingly, <i>aaNAT</i> RNAi caused not only loss of white pigment, but also loss of yellow and red pigments. This phenotype of <i>aaNAT</i> has not been reported in other insects. Our results provide new information for understanding the melanin pathway in which <i>aaNAT</i> is essential for the formation of colorless patterns.