Candidatus Liberibacter solanacearum' interacts with host psyllid vitellogenin and induces autophagy

Carrot yellows disease caused by Candidatus Liberibacter solanacearum (CLso) haplotype D constrains carrot production in Israel. CLso being transmitted by the carrot psyllid, Bactericera trigonica ensues dependence of growers on insecticidal usage to manage carrot yellows. Unveiling the molecular interactions between the psyllid vector and CLso can enable developing new, non-chemical approaches for the management of CLso-caused diseases. The role of CLso encoded proteins in CLso transmission by psyllids remains unknown, however, bacterial surface proteins are known to function in bacterial adhesion and virulence. In this study, we screened the cDNA library of B. trigonica with two CLso surface proteins, the outer membrane protein (OmpA) and flagellin as baits in a yeast-two hybrid assay. In this study, we identified the vitellogenin (Vg) protein of the psyllid as an interacting protein with the OmpA and flagellin proteins of CLso. As Vg is a well-known immune response protein with its expression tightly linked to the cellular autophagy process, we investigated the expression of the psyllid autophagy-related genes to further elucidate this interaction. Juvenile hormone (JH-III) was applied to induce the expression of Vg, whereas, thapsigargin and rapamycin were used to alter the cellular autophagy process. Our results indicate that Vg negatively regulates autophagy and vice versa. The levels of CLso also significantly increased under suppressed autophagy conditions and resulted in a significant decrease in the fecundity of the insect. Although the exact role of Vg remains unclear, our findings indicate Vg as an important component in the insect immune responses against CLso.