Abstract
“Candidatus Liberibacter solanacearum” (Lso) is a phloem-limited Gram-negative bacterium that infects crops worldwide. In North America, two haplotypes of Lso (LsoA and LsoB) are transmitted by the potato psyllid, Bactericera cockerelli (Šulc), in a circulative and persistent manner. Both haplotypes cause damaging plant diseases (e.g., zebra chip in potatoes). The psyllid gut is the first organ Lso encounters and could be a barrier for its transmission. However, little is known about the psyllid gut immune responses triggered upon Lso infection. In this study, we focused on the apoptotic response in the gut of adult potato psyllids at the early stage of Lso infection. We found that there was no evidence of apoptosis induced in the gut of the adult potato psyllids upon infection with either Lso haplotype based on microscopic observations. However, the expression of the inhibitor of apoptosis IAPP5.2 gene (survivin-like) was significantly upregulated during the period that Lso translocated into the gut cells. Interestingly, silencing of IAPP5.2 gene significantly upregulated the expression of two effector caspases and induced apoptosis in the psyllid gut cells. Moreover, RNA interference (RNAi) of IAPP5.2 significantly decreased the Lso titer in the gut of adult psyllids and reduced their transmission efficiency. Taken together, these observations suggest that Lso might repress the apoptotic response in the psyllid guts by inducing the anti-apoptotic gene IAPP5.2 at an early stage of the infection, which may favor Lso acquisition in the gut cells and facilitate its transmission by potato psyllid.
Highlights
Apoptosis, one of the programmed cell death forms, is an essential physiological process that can occur in response to intracellular or extracellular signals
We investigated the apoptotic response in the potato psyllid gut during the early stages of Liberibacter solanacearum” (Lso) infection
The results showed that both LsoA and LsoB were detectable with ~10,285 copies in pools of 50 guts of adult potato psyllids at the beginning of infection (2-day acquisition access periods (AAPs); Figure 1B)
Summary
One of the programmed cell death forms, is an essential physiological process that can occur in response to intracellular or extracellular signals. It plays a critical role in a variety of biological events including development and tissue homeostasis (Zimmermann et al, 2001; Liu et al, 2008). The extrinsic pathway is mediated by caspase-8, while the intrinsic pathway can be initiated through caspase-9. Both pathways trigger apoptosis through the cleavage of the downstream executioner proteins, caspases 3 and 7 (Elmore, 2007). IAPs are characterized by the presence of one to three baculoviral IAP repeat (BIR) domains, which are required for binding and suppression of specific cell death-inducing caspases (Silke and Meier, 2013)
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