Publications

4437

Abstract Background ‘ 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. Methods and results 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. Conclusions This study revealed haplotype-specific gene regulation potentially leading to LsoB being transmitted more efficiently by psyllid nymphs.

Abstract ‘Candidatus Mycoplasma haemolamae’ (CMhl) is a hemotropic bacterium infecting South American Camelids (SAC), whose epidemiology and clinical significance are still not fully elucidated. This study investigated CMhl by qPCR in blood samples of alpacas ( Vicugna pacos ) and llamas ( Lama glama ) in Italy in 2021–2024, characterizing CMhl haplotypes based on partial 16 S rRNA sequences and defining haematological findings in a subset of CMhl-infected animals. Statistical analysis was performed to detect potential risk factors associated with CMhl positivity. Out of 206 animals (200 alpacas and 6 llamas), CMhl was detected by qPCR in 88 (42.7%) animals. CMhl haplotype #1 and #2 were detected in 42.2% and 0.5% of the animals, respectively. Binary logistic regression analysis showed that higher CMhl positivity was significantly associated with larger herd size ( P  = 0.011), Northern Italy area of origin ( P  = 0.031) and warmer seasons ( P  = 0.003). The detection of two CMhl haplotypes confirms the high diffusion of CMhl in SAC farmed in Italy. Results confirm that CMhl usually causes subclinical infections, suggesting that antimicrobial treatment is likely not necessary based on qPCR positivity alone. Results focusing on the association of CMhl positivity with warm temperatures and large herd size suggest the need of further studies on the genetic features, epidemiology and immune response in CMhl-positive SAC from Italy, with emphasis on understanding potential vector transmission.

ABSTRACT Vector-borne transmission of plant and animal pathogens requires active engagement of the vector’s immune system, as pathogens must overcome barriers and exploit host cellular mechanisms. Candidatus Liberibacter solanacearum (CLso) and C. L. asiaticus (CLas) are gram-negative, phloem-limited bacteria transmitted by the psyllids Bactericera trigonica and Diaphorina citri , respectively. Both pathogens induce endoplasmic reticulum (ER) stress and apoptosis in the midguts of their respective vectors, promoting their transmission. The protein kinase R-like endoplasmic reticulum kinase (PERK), a key regulator of ER stress and the unfolded protein response (UPR), plays a crucial role in modulating immunity. In this study, we investigated the role of PERK in CLso-induced apoptosis. PERK expression was downregulated in CLso-infected adult psyllids and midguts, yet immunostaining revealed a significant increase in phosphorylated (active) PERK in infected midguts, despite reduced gene expression. Additionally, ER stress-inducing treatments in both infected and uninfected psyllids demonstrated that CLso infection differentially regulates PERK expression. Interestingly, similar treatments in CLas-infected and uninfected D. citri yielded different results, suggesting species-specific immune responses. Furthermore, inhibition of PERK altered the expression of apoptosis-related genes in CLso-infected psyllids, indicating its involvement in CLso-induced apoptosis. Our findings suggest that PERK and UPR play a role in initiating immune responses at the ER interface in response to CLso, ultimately contributing to apoptosis, which may aid pathogen transmission. While the precise mechanisms by which CLso controls these processes remain unclear, this study provides new insights into how vector-borne plant and potentially animal pathogens manipulate host cellular pathways to enhance their spread. IMPORTANCE This study provides valuable insights into how vector-borne pathogens manipulate host cellular pathways to promote their survival and transmission. Candidatus Liberibacter solanacearum (CLso) and C. L. asiaticus (CLas) cause severe plant diseases, such as zebra chip in potatoes, carrot yellows, and huanglongbing (citrus greening), posing significant threats to global agriculture. By revealing the role of PERK and the unfolded protein response (UPR) in CLso-induced apoptosis, our findings contribute to the growing understanding of insect immunity and pathogen-host interactions. Understanding how CLso influences ER stress and immune signaling in its psyllid vector could lead to innovative strategies to disrupt pathogen persistence and transmission, ultimately supporting disease management efforts.