Identification and gene expression profiling of toll genes in the potato psyllid (Bactericera cockerelli) in response to ‘Candidatus liberibacter solanacearum’

Abstract

The Toll signaling pathway is a key component of insect innate immunity, yet its role in hemipteran vectors and their interactions with plant pathogens remains poorly understood. The potato psyllid (Bactericera cockerelli), an important agricultural pest in the USA, transmits two haplotypes of ‘Candidatus Liberibacter solanacearum’ (LsoA and LsoB) that cause severe diseases in solanaceous crops. We characterized Toll pathway components in the B. cockerelli genome and examined their transcriptional responses during pathogen acquisition. Six Toll receptors and ten pathway-associated genes were identified in the psyllid genome. Gene expression was evaluated using RT-qPCR following exposure to the entomopathogenic fungus Beauveria bassiana (Bb-490) and infection with Lso haplotypes. The transcription of five Toll receptors was significantly induced in response to B. bassiana, indicating their potential role in antifungal defense. In contrast, Lso infection elicited haplotype-specific transcriptional responses: two Toll receptors (Toll like-1 and Toll-7) were up-regulated during LsoB acquisition, whereas only Toll-7 responded to LsoA. In addition, Spätzle-3 was induced by LsoB, while Spätzle was induced by LsoA. Persistent Lso infection did not significantly alter the transcriptional expression of Toll receptors. These findings provide new insights into immune regulation in B. cockerelli and highlight the potential of targeting Toll-mediated responses and fungal biocontrol strategies for sustainable disease management.