Publications

4669

Ticks are important vectors of bacteria belonging to the order Rickettsiales, several of which are causes zoonotic diseases. Amblyomma triste is the main vector of Rickettsia parkeri , the etiological agent responsible for most cases of human spotted fever rickettsiosis in Argentina. However, information on the circulation of rickettsial agents in protected areas of the La Plata River Hydrographic Basin, a region that includes highly urbanized environments and frequent contact between wildlife, domestic animals and humans, remains limited. The aim of this study was to investigate the presence of rickettsial bacteria in A. triste collected in protected areas of Buenos Aires Province, (La Plata River Hydrographic Basin, Argentina). Between September and December 2021, ticks were collected by vegetation flagging in four protected areas and analyzed individually. Polymerase chain reactions (PCR) for detecting the genus Rickettsia was initially performed using a simple PCR to amplify a variablesized fragment of the 23S-5S rRNA intergenic spacer. An initial PCR was performed with primers for a 16S rRNA fragment for the Anaplasmataceae family. A total of 247 adult ticks were examined. Twelve specimens (4.9%) tested positive for Rickettsia , and sequence analysis confirmed their identity as R. parkeri . Positive ticks were detected in Ciervo de los Pantanos National Park and Campos del Tuyú National Park. In addition, two specimens yielded sequences corresponding to Candidatus Midichloria sp. These findings confirm the presence of R. parkeri in A. triste populations from protected areas of the La Plata River Hydrographic Basin and provide the first evidence of Ca. Midichloria sp. in this tick species in Argentina. The results highlight the need for continued surveillance of tick-borne microorganisms in protected areas located near densely populated regions, where human exposure to infected ticks may occur.

Understanding plant-vector-pathogen interactions is essential for explaining the persistence of stolbur diseases associated with the plant pathogenic bacterium ‘ Candidatus Phytoplasma solani’ (CaPsol) in agroecosystems. This study investigates the role of crop-associated Reptalus planthoppers (Insecta: Hemiptera: Cixiidae) in shaping CaPsol epidemiology within a four-crop rotation system (sunflower, wheat, sugar beet, and maize) in Serbia under field and experimental conditions. Over a three-year period (2023–2025), nymphal surveys, adult monitoring, emergence-cage experiments, molecular identification of planthoppers, assessment of CaPsol in crops, and vector transmission assays were conducted, with a particular focus on the sunflower-wheat sequence. Sunflower was identified as a developmental host for Reptalus quinquecostatus and Reptalus panzeri , with high CaPsol infection rates detected in both the host plant and associated vectors. In contrast, wheat appeared to primarily support nymphal overwintering, while its significance as a CaPsol reservoir remains inconclusive. Furthermore, the maize-wheat sequence supported the development of R. quinquecostatus while confirming its role in the life cycle of R. panzeri . Experimental trials demonstrated efficient CaPsol transmission to sunflower but limited transmission to wheat. Despite high infection levels under field conditions, sunflower remained asymptomatic, suggesting its role as a cryptic pathogen reservoir. The findings indicate that the sunflower-wheat sequence may sustain CaPsol-infected Reptalus spp. populations across seasons, facilitating pathogen persistence within cropping systems. The study highlights the importance of integrating vector life cycle dynamics into epidemiological frameworks of stolbur diseases, particularly in crop rotations where major cultivated hosts may support in-field CaPsol pathosystems.

Huanglongbing, a destructive citrus disease of global importance that is also present in Saudi Arabia, is associated with Candidatus Liberibacter asiaticus (CLas) and remains a major threat to citrus production. Although previous studies have documented sequence variation and prophage polymorphism in CLas, broader comparisons of prophage-associated gene content remain limited. In particular, comparative orthogroup analysis of prophage gene-content conservation across geographically structured CLas populations has rarely been explored. In this study, we analyzed 42 CLas prophage genomes from Saudi Arabia and other geographic regions using a comparative orthogroup framework. OrthoFinder assigned 99.1% of predicted proteins (1825 of 1841) to 64 orthogroups, with only 16 genes remaining unassigned. A small number of rare orthogroups restricted to only a few genomes were identified, and no orthogroup was detected in all genomes. Presence–absence analyses supported a predominantly conserved prophage gene repertoire together with a small accessory component, while also indicating that apparent absences should be interpreted in light of mixed assembly status and prophage-region completeness. Saudi Arabian genomes were distributed within the broader global framework and exhibited generally similar gene-content profiles rather than a deeply separated lineage. Functional interpretation of representative orthogroups identified conserved prophage-associated genes related to replication, helicase activity, and phage packaging, whereas variable orthogroups were primarily associated with hypothetical or accessory prophage-related functions. Overall, these results are consistent with a model in which CLas prophage diversification is associated more with sequence-level variation and localized structural differences than with extensive gain or loss of prophage genes. These findings further refine current understanding of CLas genome evolution and highlight conserved prophage-associated targets that may support molecular diagnostics and epidemiological surveillance.

‘ Candidatus Liberibacter asiaticus’ ( C Las), the causal agent of citrus huanglongbing, is transmitted by the Asian citrus psyllid Diaphorina citri . While C Las-positive ( C Las+) females exhibit increased fecundity and metabolic demands, their neuroendocrine regulation mechanisms remain unclear. We propose C Las manipulates dopamine (DA) signaling to enhance psyllid fecundity and C Las proliferation. Metabolomics revealed elevated DA in C Las+ females. Silencing DA synthesis genes and receptor DcDop2 via RNAi reduced lipid reserves, fecundity, and ovarian C Las titers. Through combined in vivo and in vitro experiments, we demonstrated that the microRNA miR-31a suppresses DcDop2 expression by binding to its 3’ untranslated region. Overexpression of miR-31a resulted in decreased DcDop2 expression and C Las titers in the ovaries, eliciting phenotypic defects akin to DcDop2 knockdown. Furthermore, DcDop2 knockdown and miR-31a overexpression reduced juvenile hormone (JH) levels and adipokinetic hormone (AKH) signaling in fat bodies and ovaries. Consequently, C Las regulates the DA- DcDop2 signaling axis to improve D. citri lipid metabolism and fecundity, while simultaneously promoting its replication. These findings reveal a coevolution between C Las proliferation and ovarian development in the insect host. This discovery enhances our understanding of the molecular interplay between plant pathogens and vector insects and offers novel targets and strategies for HLB field management.