No evidence of apoptotic response of the potato psyllid, Bactericera cockerelli, to “Candidatus Liberibacter solanacearum” at the gut interface

“Candidatus Liberibacter solanacearum” (Lso) is a pathogen transmitted by the potato psyllid, Bactericera cockerelli (S ulc) (Hemiptera: Triozidae) in a persistent manner. In this study, we investigated the molecular interaction between Lso and the potato psyllid at the gut interface. Specifically, we focused on the apoptotic response of potato psyllids to the infection by two Lso haplotypes, LsoA and LsoB. Toward this end, we first quantified and localized Lso in the gut of adult psyllids. Then, we evaluated the existence of an apoptotic response in the insect gut using microscopy analyses to visualize the nuclei and the actin cytoskeleton of the gut cells, and DNA fragmentation analyses by agarose gel electrophoresis. We also performed annexin V cell death assays to detect apoptosis. Finally, we annotated apoptosis-related genes from the potato psyllid transcriptome and evaluated their expression in response to Lso infection. The results showed no cellular markers of apoptosis despite the large amount of Lso present in the psyllid gut. In addition, only three genes potentially involved in apoptosis were regulated in the psyllid gut in response to Lso: The apoptosis-inducing factor AIF3 was down-regulated in LsoA-infected psyllids while the inhibitor of apoptosis IAPP5 was down-regulated and IAP6 was up-regulated in LsoB-infected psyllids. Overall, no evidence of apoptosis was observed in the gut of potato psyllid adults in response to either Lso haplotypes. This study represents a first step towards understanding the interactions between Lso and the potato psyllid, which is crucial to develop approaches to disrupt their transmission.