title: Functional analysis of an immune gene of Spodoptera littoralis by RNAi.
abstract: Insect immune defences rely on cellular and humoral responses targeting both microbial pathogens and metazoan parasites. Accumulating evidence indicates functional cross-talk between these two branches of insect immunity, but the underlying molecular mechanisms are still largely unknown. We recently described, in the tobacco budworm Heliothis virescens, the presence of amyloid fibers associated with melanogenesis in immune capsules formed by hemocytes, and identified a protein (P102) involved in their assembly. Non-self objects coated by antibodies directed against this protein escaped hemocyte encapsulation, suggesting that P102 might coordinate humoral and cellular defence responses at the surface of foreign invaders. Here we report the identification of a cDNA coding for a protein highly similar to P102 in a related Lepidoptera species, Spodoptera littoralis. Its transcript was abundant in the hemocytes and the protein accumulated in large cytoplasmic compartments, closely resembling the localization pattern of P102 in H. virescens. RNAi-mediated gene silencing provided direct evidence for the role played by this protein in the immune response. Oral delivery of dsRNA molecules directed against the gene strongly suppressed the encapsulation and melanization response, while hemocoelic injections did not result in evident phenotypic alterations. Shortly after their administration, dsRNA molecules were found in midgut cells, en route to the hemocytes where the target gene was significantly down-regulated. Taken together, our data demonstrate that P102 is a functionally conserved protein with a key role in insect immunity. Moreover, the ability to target this gene by dsRNA oral delivery may be exploited to develop novel technologies of pest control, based on immunosuppression as a strategy for enhancing the impact of natural antagonists.
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Di Lelio
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Varricchio
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Gennaro
authors.initials: G
authors.lastname: Di Prisco
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Adriana
authors.initials: A
authors.lastname: Marinelli
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy; Istituto di Genetica e Biofisica "A. Buzzati-Traverso", CNR, via P. Castellino 111, 80131 Napoli, Italy; Istituto di Bioscienze e Biorisorse, CNR, via P. Castellino 111, 80131 Napoli, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Lasco
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Caccia
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy.
authors.forename: Morena
authors.initials: M
authors.lastname: Casartelli
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Giordana
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy.
authors.forename: Rosa
authors.initials: R
authors.lastname: Rao
authors.affiliation: Istituto di Genetica e Biofisica "A. Buzzati-Traverso", CNR, via P. Castellino 111, 80131 Napoli, Italy; Istituto di Bioscienze e Biorisorse, CNR, via P. Castellino 111, 80131 Napoli, Italy. Electronic address: silvia.gigliotti@ibbr.cnr.it.
authors.forename: Silvia
authors.initials: S
authors.lastname: Gigliotti
authors.affiliation: Dipartimento di Agraria, Università degli Studi di Napoli "Federico II", via Università 100, 80055 Portici (Napoli), Italy. Electronic address: f.pennacchio@unina.it.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pennacchio
mesh_terms: D000818:Animals; D001483:Base Sequence; D020868:Gene Silencing; D006434:Hemocytes / Q000276:immunology; D007113:Immunity, Innate; D007300:Insect Control; D019476:Insect Proteins / Q000235:genetics* / Q000276:immunology*; D007814:Larva / Q000276:immunology; D008543:Melanins / Q000378:metabolism; D008969:Molecular Sequence Data; D034622:RNA Interference; D012330:RNA, Double-Stranded; D018411:Spodoptera / Q000235:genetics* / Q000276:immunology*
chemical_list: D019476:Insect Proteins; D008543:Melanins; D012330:RNA, Double-Stranded
keywords: Encapsulation; Gene silencing; Hemocytes; Immunity; Melanization