Cloning and Characterization of karmoisin Homologue Gene (Nlka) in Two Brown Planthopper Strains with Different Eye Colors

The brown planthopper (BPH), Nilaparvata lugens, is a destructive insect pest of rice throughout Asia. Different from brown-eye color wild type, BPH also has red-eye color mutation phenotype. As a visible genetic marker, the red-eye mutant in BPH is a valuable material. To reveal the eye color mutation mechanism, a karmoisin homologue gene (named as Nlka) was cloned from BPH. And karmoisin is always deemd as a xanthommatin-related gene in other insects, encoding phenoxazinone synthetase (PHS). Nlka is consisted of 7 exons and encodes a protein with 502 amino acids (NlKA). NlKA showed high amino acid identities with its insect homologues (48.8%–51.8%). Nlka transcripts can be detected at all the developmental stages and in all tissues tested, including egg, nymph, adult, body wall, ovary, fat body, midgut and Malpighian tubule. However, no constant In/Del or non-synonymous mutation was observed between the mutant and the wild type strains. Quantitative real-time PCR experiment also showed that Nlka transcript level had no significant differences between them. These results indicated that Nlka is not the target gene causing the red-eye color mutation phenotype of BPH. Through the second structure and motif analysis, the present study also showed that all the proteins deduced from the karmoisin genes in insects may be members of monocarboxylate transporters (MCTs) rather than PHSs.