Protein interaction networks at the host-microbe interface in Diaphorina citri, the insect vector of the citrus greening pathogen

Authors: Ramsey, John - John; CHAVEZ, JUAN - University Of Washington; JOHNSON, RICHARD - University Of Washington; MAHONEY, JACLYN - Boyce Thompson Institute; MOHR, JARED - Cornell University; ROBISON, FAITH - Boyce Thompson Institute; ZHONG, XUEFEI - University Of Washington; Hall, David; MACCOSS, MICHAEL - University Of Washington; BRUCE, JAMES - University Of Washington; Heck, Michelle

Submitted to: Royal Society Open Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2017
Publication Date: 2/8/2017
Citation: Ramsey, J.S., Chavez, J., Johnson, R., Mahoney, J., Mohr, J., Robison, F., Zhong, X., Hall, D.G., Maccoss, M., Bruce, J., Cilia, M. 2017. Protein interaction networks at the host-microbe interface in Diaphorina citri, the insect vector of the citrus greening pathogen. Royal Society Open Science. https://doi.org/10.1098/rsos.160545.

Interpretive Summary: Strategies to block transmission of the citrus greening bacteria by the insect vector are needed to support citrus growers and to maintain the availability of high-quality citrus products for consumers. Using a new method to identify protein interactions in living cells called Protein Interaction Reporter, we identified an insect oxygen-binding protein as a potential master regulator of protein interactions between the insect vector and the citrus greening bacterium. The oxygen binding protein is much more abundant in insects that are carrying the citrus greening bacterium. Other interactions between the insect, the citrus greening bacterium, and beneficial microbes of the insect were identified, suggesting that the bacterium is changing the physiology of the insect to promote tree-to-tree spread.

Technical Abstract: The Asian citrus psyllid (Diaphorina citri) is the insect vector responsible for the worldwide spread of Candidatus Liberibacter asiaticus, the bacterial pathogen associated with citrus greening disease. Developmental changes in the insect vector impact pathogen transmission, such that D. citri transmission of Ca. L. asiaticus is more efficient when bacteria are acquired by nymphs as compared to adults. We hypothesize that expression changes in D. citri immune system, including the insect's commensal microbiota, occur during development and regulate vector competency. In support of this hypothesis, more proteins, with greater fold changes, were differentially expressed in response to Ca. L. asiaticus in adults as compared to nymphs, including insect proteins involved in bacterial adhesion and immunity. Compared to nymphs, adult insects had a higher titer of Ca. L. asiaticus and the bacterial endosymbionts Wolbachia, Profftella, and Carsonella. All Wolbachia and Profftella proteins differentially expressed between nymph and adult are upregulated in adults, while most differentially expressed Carsonella proteins are upregulated in nymphs. Discovery of protein interaction networks has broad applicability in the study of host-microbe relationships. Using Protein Interaction Reporter (PIR) technology, a D. citri hemocyanin protein highly upregulated in response to Ca. L. asiaticus was found to physically interact with the Ca. L. asiaticus coenzyme A (CoA) biosynthesis enzyme phosphopantothenoylcysteine synthetase/decarboxylase. Ca. L. asiaticus pantothenate kinase, which catalyzes the rate-limiting step of CoA biosynthesis, was found to interact with a D. citri myosin protein. Two Carsonella enzymes involved in histidine and tryptophan biosynthesis were found to physically interact with D. citri proteins. These co-evolved protein interaction networks at the host-microbe interface are highly specific targets for controlling the insect vector responsible for the spread of citrus greening.