title: The structural sheath protein of aphids is required for phloem feeding.
abstract: Aphids produce two types of saliva that mediate their interactions with plants. Watery saliva is secreted during cell penetration and ingestion, whereas gel saliva is secreted during stylet movement through the apoplast where it forms a sheath around the stylet to facilitate penetration and seal puncture sites on cell membranes. In order to study the function of the sheath when aphids interact with plants, we used RNA interference (RNAi) to silence the aphid structural sheath protein (SHP) in the pea aphid Acyrthosiphon pisum. The injection of 50 ng of double stranded RNA completely disrupted sheath formation, as confirmed by scanning electron microscopy. Aphid behavior was monitored using the electrical penetration graph technique, revealing that disrupted sheath formation prevented efficient long-term feeding from sieve tubes, with a silencing effect on reproduction but not survival. We propose that sealing the stylet penetration site in the sieve tube plasma membrane is part of a two-step mechanism to suppress sieve-tube occlusion by preventing calcium influx into the sieve tube lumen. The SHP is present in several aphid species and silencing has a similar impact to aphid-resistant plants, suggesting that SHP is an excellent target for RNAi-mediated pest control.
authors.affiliation: Institute for Phytopathology and Applied Zoology, Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32, D-35392, Giessen, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Will
authors.affiliation: Institute for Phytopathology and Applied Zoology, Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32, D-35392, Giessen, Germany; Project Group "Bioresources", Fraunhofer Institute of Molecular Biology and Applied Ecology IME, Winchesterstrasse 2, D-35394 Giessen, Germany. Electronic address: Andreas.Vilcinskas@agrar.uni-giessen.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Vilcinskas
mesh_terms: D000818:Animals; D001042:Aphids / Q000378:metabolism / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology; D019476:Insect Proteins / Q000378:metabolism / Q000502:physiology; D052585:Phloem / Q000502:physiology; D034622:RNA Interference; D012463:Saliva / Q000737:chemistry / Q000378:metabolism*; D031307:Vicia faba / Q000469:parasitology*
chemical_list: D019476:Insect Proteins
keywords: Acyrthosiphon pisum; Aphid; Behavior; Phloem; RNAi; Salivary sheath