Color morphology of Diaphorina citri influences interactions with its bacterial endosymbionts and 'Candidatus Liberibacter asiaticus'

PLoS One. 2019 May 16;14(5):e0216599. doi: 10.1371/journal.pone.0216599. eCollection 2019.

Abstract

Diaphorina citri is a vector of 'Candidatus Liberibacter asiaticus,' (CLas), associated with Huanglongbing, (HLB, or citrus greening) disease in citrus. D. citri exhibits three different color morph variants, blue, gray and yellow. Blue morphs have a greater capacity for long-distance flight as compared to non-blue morphs, but little else is known about how color morphology influences vector characteristics. In this study, we show that the color morphology of the insect is derived from pigmented cells of the fat body. Blue morphs acquire a lower level of CLas in their bodies from infected trees as compared to their gray and yellow conspecifics, referred to in this paper collectively as non-blue morphs. Accordingly, CLas titer in citrus leaves inoculated by non-blue insects was 6-fold higher than in leaves inoculated by blue insects. Blue color morphs harbored lower titers of Wolbachia and 'Candidatus Profftella armatura,' two of the D. citri bacterial endosymbionts. Expression of hemocyanin, a copper-binding oxygen transport protein responsible for the blue coloration of hemolymph of other arthropods and mollusks, was previously correlated with blue color morphology and is highly up-regulated in insects continuously reared on CLas infected citrus trees. Based on our results, we hypothesized that a reduction of hemocyanin expression would reduce the D. citri immune response and an increase in the titer of CLas would be observed. Surprisingly, a specific 3-fold reduction of hemocyanin-1 transcript levels using RNA silencing in blue adult D. citri morphs had an approximately 2-fold reduction on the titer of CLas. These results suggest that hemocyanin signaling from the fat body may have multiple functions in the regulation of bacterial titers in D. citri, and that hemocyanin is one of multiple psyllid genes involved in regulating CLas titer.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Citrus / microbiology*
  • Citrus / parasitology
  • Color
  • Hemiptera / microbiology*
  • Hemiptera / physiology
  • Hemocyanins / metabolism
  • Host-Pathogen Interactions*
  • Insect Vectors / microbiology*
  • Insect Vectors / physiology
  • Plant Diseases / microbiology*
  • Rhizobiaceae / isolation & purification
  • Rhizobiaceae / physiology*
  • Symbiosis*

Substances

  • Hemocyanins

Grants and funding

Funding for this project was provided to Michelle Heck and David Hall by the California Citrus Research Board grants 5300-163 and 5300-155, USDA NIFA Specialty Crops Program grant 60-8062-6-002 and the USDA Agricultural Research Service projects 8062-22410-006-00D and 6618-22320-001-00D. The funding organizations played no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.