title: Foliar aphid feeding recruits rhizosphere bacteria and primes plant immunity against pathogenic and non-pathogenic bacteria in pepper.
abstract: OBJECTIVE
  Plants modulate defence signalling networks in response to different biotic stresses. The present study evaluated the effect of a phloem-sucking aphid on plant defence mechanisms in pepper (Capsicum annuum) during subsequent pathogen attacks on leaves and rhizosphere bacteria on roots.
  
  
  METHODS
  Plants were pretreated with aphids and/or the chemical trigger benzothiadiazol (BTH) 7 d before being challenged with two pathogenic bacteria, Xanthomonas axonopodis pv. vesicatoria (Xav) as a compatible pathogen and X. axonopodis pv. glycines (Xag) as an incompatible (non-host) pathogen.
  
  
  RESULTS
  Disease severity was noticeably lower in aphid- and BTH + aphid-treated plants than in controls. Although treatment with BTH or aphids alone did not affect the hypersensitive response (HR) against Xag strain 8ra, the combination treatment had a synergistic effect on the HR. The aphid population was reduced by BTH pretreatment and by combination treatment with BTH and bacterial pathogens in a synergistic manner. Analysis of the expression of the defence-related genes Capsicum annum pathogenesis-related gene 9 (CaPR9), chitinase 2 (CaCHI2), SAR8·2 and Lipoxygenase1 (CaLOX1) revealed that aphid infestation resulted in the priming of the systemic defence responses against compatible and incompatible pathogens. Conversely, pre-challenge with the compatible pathogen Xav on pepper leaves significantly reduced aphid numbers. Aphid infestation increased the population of the beneficial Bacillus subtilis GB03 but reduced that of the pathogenic Ralstonia solanacearum SL1931. The expression of defence-related genes in the root and leaf after aphid feeding indicated that the above-ground aphid infestation elicited salicylic acid and jasmonic acid signalling throughout the whole plant.
  
  
  CONCLUSIONS
  The findings of this study show that aphid feeding elicits plant resistance responses and attracts beneficial bacterial populations to help the plant cope with subsequent pathogen attacks.
authors.affiliation: Molecular Phytobacteriology Laboratory, Systems and Synthetic Biology Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon 305-806, South Korea.
authors.forename: Boyoung
authors.initials: B
authors.lastname: Lee
authors.forename: Soohyun
authors.initials: S
authors.lastname: Lee
authors.forename: Choong-Min
authors.initials: CM
authors.lastname: Ryu
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000378:metabolism; D001042:Aphids / Q000502:physiology; D001412:Bacillus subtilis / Q000502:physiology; D002212:Capsicum / Q000235:genetics / Q000276:immunology* / Q000382:microbiology* / Q000469:parasitology; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006790:Host-Parasite Interactions / Q000276:immunology; D054884:Host-Pathogen Interactions / Q000276:immunology*; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D057865:Plant Immunity / Q000502:physiology; D018515:Plant Leaves / Q000276:immunology / Q000382:microbiology / Q000469:parasitology*; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000382:microbiology*; D011551:Pseudomonas fluorescens / Q000502:physiology; D043368:Ralstonia solanacearum / Q000502:physiology; D058441:Rhizosphere; D012988:Soil Microbiology; D013830:Thiadiazoles; D014774:Virulence; D014974:Xanthomonas / Q000502:physiology*
chemical_list: D000890:Anti-Infective Agents; D010940:Plant Proteins; D013830:Thiadiazoles; C053376:pathogenesis-related proteins, plant; C015700:benzo-1,2,3-thiadiazole