Role of the endoplasmic reticulum (ER) in the interactions and transmission of 'Candidatus Liberibacter solanacearum' by the carrot psyllid Bactericera trigonica

Candidatus Liberibacter solanacerum (CLso) is transmitted by the carrot psyllid Bactericera trigonica in a persistent and propagative mode and causes carrot yellows disease, inflicting significant economic losses in many countries. Understanding the transmission of CLso by psyllids is fundamental to devise sustainable management strategies. Persistent transmission involves critical steps of adhesion, cell invasion, and replication inside the gut cells before passage to the hemolymph. We used transcriptomics, microscopy and mRNA silencing in whole insects and dissected organs to search for insect proteins involved in the transmission. Our study shows that genes involved in proper functionality of the endoplasmic reticulum (ER) were upregulated in CLso infected samples. Notably, genes from the endoplasmic reticulum associated degradation (ERAD) and the unfolded protein response (UPR) pathway were overexpressed after CLso infection, including DERLIN-1, SELENOPROTEIN-1 and UBIQUITIN LIGASE RNF-185. Silencing of DERLIN-1 revealed its important role in CLso transmission and maintaining its levels in gut cells. Upregulation of the ERAD and UPR pathway indicate induction of ER stress by CLso in the psyllid vector. The role of ER in bacteria–host interactions is well documented and the specific role and importance of ER-associated genes in this and similar systems require further investigations.