Liberibacter solanacearum interacts with host psyllid vitellogenin with its membrane proteins

Candidatus Liberibacter solanacearum (CLso) haplotype D, transmitted by the carrot psyllid Bactericera trigonica is a major constraint in carrot production in Israel. Understanding the molecular interactions between the psyllid vector and CLso can facilitate non-chemical approaches for controlling CLso caused-diseases. In this study, we used CLso outer membrane protein (OmpA) and flagellin as baits to screen for psyllid interacting proteins in a yeast-two hybrid assay. We identified psyllid vitellogenin (Vg) protein to interact with both OmpA and flagellin of CLso. As Vg is often involved in innate immunity with its expression tightly linked to autophagy, a major component of the immune response in the cell, we also analyzed the expression of autophagy-related genes to further elucidate this interaction. We used the juvenile hormone (JH-III) to induce the expression of Vg, thapsigargin for suppressing autophagy, and rapamycin for inducing autophagy. The results revealed that Vg negatively regulates autophagy and vice versa. JH-III induced Vg expression significantly suppressed autophagy and, the levels of CLso significantly increased resulting in a significant mortality of the insect. Although the specific role of Vg remains obscure, the findings presented here identify Vg as an important component in the insect immune responses against CLso and may help in understanding the initial molecular response in the vector against Liberibacter.