‘Candidatus Liberibacter asiaticus’ minimally alters expression of immunity and metabolism proteins in the hemolymph of Diaphorina citri, the insect vector of Huanglongbing

Authors: KRUSE, ANGELA - Cornell University; Ramsey, John - John; JOHNSON, RICHARD - University Of Washington; Hall, David; MACCOSS, MICHAEL - University Of Washington; Heck, Michelle

Submitted to: Journal of Proteome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2018
Publication Date: 9/7/2018
Citation: Kruse, A., Ramsey, J.S., Johnson, R., Hall, D.G., MacCoss, M., Heck, M.L. 2018. ‘Candidatus Liberibacter asiaticus’ minimally alters expression of immunity and metabolism proteins in the hemolymph of Diaphorina citri, the insect vector of Huanglongbing. Journal of Proteome Research. 17(9):2995-3011. https://doi.org/10.1021/acs.jproteome.8b00183.
DOI: https://doi.org/10.1021/acs.jproteome.8b00183

Interpretive Summary: Citrus greening disease is a fatal disease of citrus and is destroying the Florida citrus industry. The disease is now also found in California and Texas. The Asian citrus psyllid (ACP, Diaphorina citri) is the insect vector responsible for the spread of citrus greening disease. The objective of this work is to increase our understanding of the immune response of the ACP to the bacteria that causes citrus greening disease. The blood (hemolymph) plays an important role in the insect immune response, and we performed this research to discover which proteins in the blood of the ACP are involved in the transmission of the citrus greening bacterium. Out of 2000 proteins which we identified in the insect blood, only 13 were found at different abundance between healthy ACP and ACP exposed to CLas through feeding on diseased plants. The proteins found at higher levels in ACP which have been exposed to CLas include immunity and metabolism proteins. This research reveals specific details about the response of CLas to the citrus greening pathogen which informs the development of novel control strategies.

Technical Abstract: Huanglongbing (HLB), also known as citrus greening disease, is the most serious disease of citrus plants in the United States and worldwide. It is associated with the Gram-negative bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), which is transmitted between host plants by the insect vector the Asian citrus psyllid (ACP, Diaphorina citri) in a circulative pathway involving specific interactions with various insect tissues, including the hemolymph, a fluid akin to insect blood. High resolution quantitative mass spectrometry was performed to investigate the effect of CLas exposure on ACP hemolymph at the proteome level. In contrast to the broad proteome effects on hundreds of proteins previously reported in gut and whole insect proteome analyses, the effect of CLas on the hemolymph was observed to be highly specific, restricted to key immunity and metabolism pathways. The most abundant hemolymph proteins included several lipid-binding proteins and proteins involved in lipid metabolism, including ten different variants of the lipoprotein vitellogenin. Vitellogenin proteins have predicted functions in reproduction and immunity, and several were found at higher levels in hemolymph of CLas-exposed ACP. This research reveals changes in ACP metabolism in response to CLas exposure, which may impact life history traits critical to the ability of the insect to transmit the citrus greening pathogen between trees.