Treatment of Rapamycin and Evaluation of an Autophagic Response in the Gut of Bactericera cockerelli (Sulč)

SIMPLE SUMMARY: In North America, the Gram-negative plant bacterial pathogen ‘Candidatus Liberibacter solanacearum’ (Lso) imposes a serious threat to most solanaceous crops, and in potato, it causes zebra chip disease. Lso is transmitted by the potato psyllid, Bactericera cockerelli (Šulc), in a circulative and persistent manner. Our previous study showed that autophagy might be involved in the transmission, but tools to evaluate autophagy in this species have not been validated. The results showed that a 24 h ingestion of rapamycin resulted in increased mortality and could induce autophagy as determined via microscopy and measurement of the autophagic flux by Western blot. This study validated rapamycin as an autophagy inducer and validated tools to assess the response in the gut of adult potato psyllid. ABSTRACT: Autophagy is a catabolic process that results in the autophagosomic–lysosomal degradation of bulk cytoplasmic content, abnormal protein aggregates, and excess of/or damaged organelles to promote cell survival. Autophagy is also a component of innate immunity in insects and is involved in the clearance of pathogens, including bacteria. The potato psyllid, Bactericera cockerelli, transmits the plant bacterial pathogen ‘Candidatus Liberibacter solanacearum’ (Lso) in the Americas and causes serious damage to solanaceous crops. Our previous studies showed that autophagy could be involved in the psyllid response to Lso and could affect pathogen acquisition. However, the tools to evaluate this response have not been validated in psyllids. To this end, the effect of rapamycin, a commonly used autophagy inducer, on potato psyllid survival and the expression of autophagy-related genes was evaluated. Further, the autophagic activity was assessed via microscopy and by measuring the autophagic flux. Artificial diet-feeding assays using rapamycin resulted in significant psyllid mortality, an increase in the autophagic flux, as well as an increase in the amount of autolysosomes. This study represents a stepping stone in determining the role of autophagy in psyllid immunity.