Morphological abnormalities and cell death in the Asian citrus psyllid (Diaphorina citri) midgut associated with Candidatus Liberibacter asiaticus

Authors: GHANIM, MURAD - Volcani Center (ARO); FATTAH-HOSSEINI, SOMAYEH - Boyce Thompson Institute; LEVY, AMIT - Boyce Thompson Institute; Heck, Michelle

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2016
Publication Date: 9/15/2018
Citation: Ghanim, M., Fattah-Hosseini, S., Levy, A., Heck, M.L. 2018. Morphological abnormalities and cell death in the Asian citrus psyllid (Diaphorina citri) midgut associated with Candidatus Liberibacter asiaticus. Scientific Reports. 6:33418. doi:10.1038/srep33418.
DOI: https://doi.org/10.1038/srep33418

Interpretive Summary: The bacterium associated with the fatal citrus greening disease is transmitted by the small flying insect vector known as the Asian citrus psyllid. Citrus greening has decimated Florida’s citrus industry worth nine billion dollars annually, and the pathogen and vector are emerging in other US citrus growing areas. Immediate and sustainable measures for controlling citrus greening are urgently needed. As an alternative to pesticides, which are harmful to the environment and ineffective, disrupting bacterial transmission by psyllids represents an improved disease management strategy. Although the bacteria infect many tissues in the insect including blood, salivary glands, gut, ovaries, and muscle, the first key intervention point may be crossing from the gut to the blood. ARS scientists and university partners have observed gut cell abnormalities in insects that had ingested the bacteria. These abnormalities were associated with indicators of programed cell death, a phenomenon where the bacteria-infected insect cells actually commit suicide to prevent further spread of the bacteria inside the insect. The discovery opens up new avenues of research on preventing the spread of the bacteria by psyllids.

Technical Abstract: Candidatus Liberibacter asiaticus (CLas) is a phloem-limited, gram-negative, fastidious bacterium that is associated with the development of citrus greening disease, also known as Huanglongbing (HLB). CLas is transmitted by the Asian citrus psyllid (ACP) Diaphorina citri, in a circulative manner. Two major barriers to transmission within the insect are the midgut and the salivary glands. We performed a thorough microscopic analysis within the insect midgut following exposure to CLas-infected citrus trees. We observed changes in nuclear architecture, including pyknosis and karyorrhexis as well as changes to the actin cytoskeleton in CLas-exposed midgut cells. Further analyses showed that the changes are likely due to the activation of programmed cell death as assessed by Annexin V staining and DNA fragmentation assays. These results suggest that exposure to CLas-infected trees induces apoptotic responses in the psyllid midgut that should be further investigated. Understanding the adaptive significance of the apoptotic response has the potential to create new approaches for controlling HLB.