Diaphorina citri nymphs are resistant to morphological changes induced by “Candidatus Liberibacter asiaticus” in midgut epithelial cells

Authors: MANN, MARINA - Boyce Thompson Institute; FATTAH-HOSSEINI, SOMAYEH - Boyce Thompson Institute; Ammar, Eldesouky; STRANGE, RICHARD - University Of Florida; WARRICK, ERICA ROSE - University Of Florida; STURGEON, KASIE - University Of Florida; Shatters, Robert - Bob; Heck, Michelle

Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2018
Publication Date: 1/8/2018
Citation: Mann, M., Fattah-Hosseini, S., Ammar, E., Strange, R., Warrick, E., Sturgeon, K., Shatters, R.G., Heck, M.L. 2018. Diaphorina citri nymphs are resistant to morphological changes induced by “Candidatus Liberibacter asiaticus” in midgut epithelial cells. Infection and Immunity. 86(4):e00889-17. https://doi.org/10.1128/IAI.00889-17.
DOI: https://doi.org/10.1128/IAI.00889-17

Interpretive Summary: The bacterium “Candidatus Liberibacter asiaticus” is associated with citrus greening disease and is spread in citrus groves by a tiny insect, the Asian citrus psyllid (Diaphorina citri). The bacterial infection attacks all citrus varieties worldwide, causing reduced fruit marketability and tree death, with no cure available. For adult insects to spread the bacterium, the bacterium must enter into the insect gut cells while the insects are in the nymph stage, or the juvenile form of the insect. In this work, ARS scientists highlight a striking difference between the guts of nymph and adult psyllids. In adults, the bacterium causes massive changes in the shape of the nuclei inside cells of the insect’s gut. The nuclei are critical to gut function, as they regulate how the insect responds to its environment, including infection with the citrus greening bacterium. These massive gut cell nuclei changes in response to the bacterium do not occur in nymph guts, a result that is a clue into why the bacteria have to enter into the gut while the insect is in the nymphal stage. Scientists also show that a microbial partner in the psyllid gut, called Wolbachia, may also play a role in allowing the citrus greening bacterium to infect the gut of the insect. Understanding why the citrus greening pathogen induces cellular changes in adult guts but not nymphs and the extent to which the other microbes in the psyllid gut play a role in the spread of the bacterium are critical to the development of innovative disease control strategies that block pathogen transmission.

Technical Abstract: “Candidatus Liberibacter asiaticus” is the causative bacterium associated with citrus greening disease. “Ca. L. asiaticus” is transmitted by Diaphorina citri more efficiently when it is acquired by nymphs rather than adults. Why this occurs is not known. We compared midguts of D. citri reared on healthy or “Ca. L. asiaticus”-infected citrus trees using quantitative PCR, confocal microscopy, and mitochondrial superoxide staining for evidence of oxidative stress. Consistent with its classification as propagative, “Ca. L. asiaticus” titers were higher in adults as compared to nymphs. Our previous work showed that adult D. citri show basal levels of karyorrhexis, (fragmentation of the nucleus), in midgut epithelial cells which is increased in severity and frequency in response to “Ca. L. asiaticus”. Here, we show that nymphs exhibit lower levels of early-stage karyorrhexis as compared to adults and are refractory to the induction of advanced karyorrhexis by “Ca. L. asiaticus” in the midgut epithelium. MitoSox Red staining showed that guts of infected adults, particularly males, experience oxidative stress in response to “Ca. L. asiaticus.” A positive correlation between the titers of “Ca. L. asiaticus” and the Wolbachia endosymbiont was observed in adult and nymph midguts, suggesting an interplay between these bacteria during development. We hypothesize that the resistance of the nymph midgut to late stage karyorrhexis through as yet unknown molecular mechanisms benefits “Ca. L. asiaticus” for efficient invasion of midgut epithelial cells, which may be a factor explaining the developmental dependency of “Ca. L. asiaticus” acquisition by this vector.