Ion transport peptide (ITP) regulates wing expansion and cuticle melanism in the brown planthopper, Nilaparvata lugens.

Ion transport peptide (ITP) and its alternatively spliced homologous ITP-like (ITPL) products play important roles in various insect developmental processes. We found for the first time that alternative 5' untranslated regions (5' UTRs) of ITPL (NilluITPLs-1, -2, -3 and -4) control spatiotemporal expression in the brown planthopper, Nilaparvata lugens, as demonstrated by reverse-transcription quantitative PCR. By using an alternative 5' UTR, NilluITPL-1 was expressed exclusively in the male reproductive system, resulting in the production of the NilluITPL seminal fluid protein. Interestingly, NilluITPLs-3 and -4 were expressed exclusively in the integument, indicating a specialized function for NilluITPL during ecdysis and eclosion. We investigated the functions of NilluITP and NilluITPL using RNA interference (RNAi). We did not observe apparent phenotypes when expression of NilluITPLs was suppressed. However, when NilluITP expression was suppressed, the insect exhibited melanism and failed wing expansion, indicating that NilluITP is a neuropeptide associated with wing expansion in addition to bursicon. Additionally, in contrast to bursicon, the insects showed increased melanism when NilluITP was eliminated by RNAi. Unlike previous studies of ITP/ITPL in other species, NilluITP was very important in the control of N. lugens postecdysial behaviours but was not critical during ecdysis. Thus, the functions of ITP and ITPL are more complex in insects than previously thought.