Combining 'omics and microscopy to visualize interactions between the Asian citrus psyllid vector and the Huanglongbing pathogen Candidatus Liberibacter asiaticus in the insect gut

Authors: KRUSE, ANGELA - Cornell University; FATTAH-HOSSEINI, SOMAYEH - Boyce Thompson Institute; SAHA, SURYA - Boyce Thompson Institute; JOHNSON, RICHARD - University Of Washington; WARWICK, ERICA ROSE - University Of Florida; STURGEON, KASIE - University Of Florida; MUELLER, LUKAS - Boyce Thompson Institute; MACCOSS, MICHAEL - University Of Washington; Shatters, Robert - Bob; Heck, Michelle

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2017
Publication Date: 6/20/2017
Citation: Kruse, A., Fattah-Hosseini, S., Saha, S., Johnson, R., Warwick, E., Sturgeon, K., Mueller, L., Maccoss, M.J., Shatters, R.G., Cilia, M. 2017. Combining 'omics and microscopy to visualize interactions between the Asian citrus psyllid vector and the Huanglongbing pathogen Candidatus Liberibacter asiaticus in the insect gut. PLoS One. https://doi.org/10.1371/journal.pone.0179531.

Interpretive Summary: The Asian citrus psyllid is the insect vector responsible for the spread of Huanglongbing, also known as citrus greening disease. Control of the psyllid is the most effective way of preventing the spread of Huanglongbing. The Huanglongbing-associated bacterium, Candidatus Liberibacter asiaticus (CLas) is deadly to citrus trees and has to spread throughout the body of the psyllid vector before it can infect a new tree. This study revealed that the process of CLas entry, also known as acquisition, into the insect gut is regulated by highly tuned interactions between psyllid and CLas genes and proteins. Surprisingly, we showed that a second insect-infecting bacterium present in the psyllid gut, Wolbachia, may participate in the entry of CLas into psyllid cells. We used microscopy to visualize CLas and Wolbachia in the insect gut and showed these two bacteria can reside within the same gut cells but do not overlap within individual cells. Our results show that CLas has more diverse patterns of localization in the gut as compared to Wolbachia. We describe how this knowledge can be used to develop interdiction molecules that block the CLas bacteria from entering into psyllid guts and ultimately transmission in the grove.

Technical Abstract: Huanglongbing, or citrus greening disease, is an economically devastating bacterial disease of citrus. It is associated with infection by the gram-negative bacterium Candidatus Liberibacter asiaticus (CLas). CLas is transmitted by Diaphorina citri, the Asian citrus psyllid (ACP). For insect transmission to occur, CLas must be ingested during feeding on infected phloem sap and cross the gut barrier to gain entry into the insect vector. To investigate the effects of CLas exposure at the gut-pathogen interface, we performed RNAseq and mass spectrometry-based proteomics to analyze the transcriptome and proteome, respectively, of ACP gut tissue. CLas exposure resulted in changes in pathways involving the TCA cycle, iron metabolism, insecticide resistance and the insect’s immune system. We identified 83 long non-coding RNAs that are responsive to CLas, two of which appear to be specific to the ACP. Proteomics analysis also enabled us to determine that Wolbachia, a symbiont of the ACP, undergoes proteome regulation when CLas is present. Fluorescent in situ hybridization (FISH) confirmed that Wolbachia and CLas inhabit the same ACP gut cells, but do not co-localize within those cells. Wolbachia cells are prevalent throughout the gut epithelial cell cytoplasm, and Wolbachia titer is more variable in the guts of CLas exposed insects. CLas is detected on the luminal membrane, in puncta within the gut epithelial cell cytoplasm, along actin filaments in the gut visceral muscles, and rarely, in association with gut cell nuclei. Our study provides a snapshot of how the psyllid gut copes with CLas exposure and provides information on pathways and proteins for targeted disruption of CLas-vector interactions at the gut interface.