# Accumulation and transmission dynamics of ‘Candidatus liberibacter solanacearum’ haplotypes A and B by potato psyllid nymphs: bioassay and transcriptomic insights

## TL;DR

This study explores how two variants of a plant pathogen are acquired and transmitted by insect nymphs, revealing differences in their transmission efficiency and effects on the insect's gut.

## Contribution

The study reveals haplotype-specific gene regulation in psyllid nymphs upon acquisition of LsoA and LsoB, linking these responses to transmission efficiency.

## Key findings

- LsoB accumulates faster and is transmitted earlier than LsoA by potato psyllid nymphs.
- LsoA and LsoB induce distinct transcriptional responses in the nymph gut, affecting different biological processes.
- Transcriptional changes are more pronounced after 5 days of pathogen acquisition compared to 1 day.

## Abstract

‘Candidatus Liberibacter solanacearum’ (Lso) is a phloem-limited bacterial pathogen causing significant diseases in solanaceous crops. In the United States, haplotypes A and B are transmitted by the potato psyllid Bactericera cockerelli. We previously identified differences in their acquisition and transmission between adults and nymphs. The present study characterized the dynamics of LsoA and LsoB acquisition and transmission by nymphs and examined the transcriptional responses of the nymphal gut upon their acquisition.

Nymphs were exposed to LsoA- or LsoB-infected plants for 1, 3, 5, or 7 days to measure the bacterial accumulation and for 8 days to assess the transmission efficiency following sequential inoculation of tomato plants. Quantitative PCR showed that LsoB accumulated to higher levels than LsoA after 3 days of acquisition. Following the sequential inoculation, LsoB was transmitted earlier than LsoA indicating a shorter latency period. RNA-seq analysis of the guts following a 1- and 5-day acquisition access periods revealed a greater transcriptional regulation at 5 days than at 1 day. Furthermore, the responses were haplotype-specific: LsoA primarily affected genes involved in protein translation, ER stress, and cell cycle regulation, whereas LsoB regulated genes involved in autophagy, apoptosis, and immune pathways.

This study revealed haplotype-specific gene regulation potentially leading to LsoB being transmitted more efficiently by psyllid nymphs.

The online version contains supplementary material available at 10.1007/s11033-025-11417-y.