Peptidomics-driven insights into Diaphorina citri physiology and response to ‘Candidatus Liberibacter asiaticus’

Authors: Fleites, Laura; IGWE, DAVID - Boyce Thompson Institute; JOHNSON, RICHARD - University Of Washington; Hall, David; Nachman, Ronald; MACCOSS, MICHAEL - University Of Washington; Heck, Michelle

Submitted to: Journal of Proteome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2020
Publication Date: 3/10/2020
Citation: Fleites, L.A., Igwe, D., Johnson, R., Hall, D.G., Nachman, R.J., Maccoss, M., Heck, M.L. 2020. Peptidomics-driven insights into Diaphorina citri physiology and response to ‘Candidatus Liberibacter asiaticus’. Journal of Proteome Research. https://doi.org/10.1021/acs.jproteome.9b00509.
DOI: https://doi.org/10.1021/acs.jproteome.9b00509

Interpretive Summary: Huanglongbing (HLB), also referred to as citrus greening disease, is the most serious disease of citrus world-wide. In the USA, HLB in citrus is associated with plant infection by bacterium called CLas that is spread by a tiny invasive insect called the Asian citrus psyllid. Current management strategies that rely on insect vector control using pesticides are ineffective at controlling the spread of HLB in groves. Insect neuropeptides are produced by a variety of insect tissues and control different facets of insect physiology, such as flight, molting and reproduction. In this work, ARS scientists and University partners used quantitative mass spectrometry to discover and quantify neuropeptides and other peptides in the psyllid that change in structure and abundance when the insects are feeding on HLB-infected trees. The results show that at this level of metabolism, CLas-infected trees have a major impact on the psyllid vector, in contrast to the effects of CLas on other types of psyllid molecules. Feeding a subset of analogs of these neuropeptides causes an acceleration of psyllid death, indicating that these peptides may prove to be a new source of insecticides.

Technical Abstract: As the primary vector of ‘Candidatus Liberibacter asiaticus’ (CLas), the bacteria associated with Huanglongbing (HLB) disease of citrus, the Asian citrus psyllid (ACP; Diaphorina citri) has caused severe damage to the citrus industry across the globe. This hemipteran insect forms an intimate relationship with CLas, where the bacteria infect numerous insect tissues during the circulative, propagative transmission process. CLas-infected insects exhibit changes in host plant seeking behavior, fecundity, flight and immunity consistent with vector manipulation, but the molecular basis of these phenotypes is poorly understood. In this work, we leveraged a previously optimized peptidomics extraction protocol coupled with high-resolution mass spectrometry to quantitatively compare the peptidomes of healthy and CLas-infected psyllids. This approach has uncovered an unprecedented response to CLas exposure in adult ACP: almost half of the proteins identified (47.2%) were up- or down-regulated in CLas infected psyllids and numerous peptidoforms, or native peptide isoforms, were specific to psyllids reared on CLas-infected or healthy trees. An array of candidate bioactive peptides were identified, including peptides with strong structural or sequence homology to antimicrobial peptides. Of particular interest, 8 of 13 proteins from the psyllid’s bacterial symbiont, ‘Candidatus Profftella armatura’, including several stress-responsive proteins, and 11 of 14 psyllid neuropeptide precursors detected were down-regulated with CLas exposure, providing evidence of symbiotic proteome plasticity and neuromodulation as a result of bacterial infection. Furthermore, a biostable analog of cardio acceleratory peptide 2b, one of the differentially regulated neuropeptides, expedited ACP mortality in artificial diet feeding experiments. The peptides described herein hold promise as environmentally friendly alternatives to pesticides and antimicrobials, which are sorely needed for the control of HLB and viability of the US citrus industry.