karmoisin and cardinal ortholog genes participate in the ommochrome synthesis of Nilaparvata lugens (Hemiptera: Delphacidae).

Ommochrome is the major source for eye coloration of all insect species so far examined. Phenoxazinone synthetase (PHS) has always been regarded as the terminal step enzyme for ommochrome formation, which is encoded by cardinal or karmoisin gene. Our previous study indicated that the karmoisin ortholog gene (Nl-karmoisin) product in the brown planthopper (BPH) was a monocarboxylate transporter, while not a PHS. Here, based on the full-length cDNA, the cardinal ortholog gene in BPH (Nl-cardinal) product was predicted to be a haem peroxidase rather than a PHS either. We suggested that neither karmoisin nor cardinal encodes the PHS for the first time, whether the PHS participated in BPH eye pigmentation needs further research. Nymphal RNAi experiments showed that knockdown Nl-cardinal transcript led the BPH ocelli and compound eye color changed from brown to red, while knockdown Nl-karmoisin only made the ocelli present red phenotype. Notably, not only the Nl-cardinal transcript, dscd injection (Nl-cardinal targeting dsRNA) also significantly reduced the Nl-karmoisin transcript by 33.7%, while dska (Nl-karmoisin targeting dsRNA) injection did not significantly change the Nl-cardinal transcript. Considering above RNAi and qRT-PCR results, we propose that Nl-cardinal play a more important role in ommchrome synthesis than Nl-karmoisin, and it may be an upstream gene of Nl-karmoisin. The present study suggested that both karmoisin and cardinal ortholog genes play a role in ommochrome synthesis in a hemimetabolous insect. This article is protected by copyright. All rights reserved.