Candidatus Liberibacter Solanacearum Research Articles

Symbiont infection and psyllid haplotype influence phenotypic plasticity during host switching events

Abstract Many herbivorous insect species exhibit phenotypic plasticity when using multiple hosts, which facilitates survival in heterogeneous host environments. Physiological host acclimation is an important part of it, yet the effects of host acclimation on insect feeding behaviour are not well studied, particularly for insect vectors of plant pathogens. We studied the combined effects of host acclimation and infection with a plant pathogenic symbiont on feeding behaviour of Bactericera cockerelli, an oligophagous psyllid widespread in both crop and natural habitats that feed primarily on Solanaceae and transmit an economically important plant pathogen, Candidatus Liberibacter solanacearum (CLso). We used a factorial design and the electrical penetration graphing technique to disentangle the effects of host acclimation, CLso infection and psyllid haplotype on the within‐plant feeding behaviour of B. cockerelli during conspecific and heterospecific host switches. This approach allows to connect phenotypic plasticity with the role of B. cockerelli as a vector by quantifying the frequency and duration of behaviours involved in CLso transmission. We found significant reductions in multiple metrics of B. cockerelli feeding efficiency, exacerbated by infection with CLso, which could lead to reduced transmission of this pathogen. Psyllid genotype was also important; the Central haplotype exhibited less dramatic changes in feeding efficiency than the Western haplotype during heterospecific host switches. Our study shows that host acclimation and heterospecific host switching directly alter feeding behaviours underlying pathogen transmission, and that the magnitude of feeding efficiency reductions depends on both host genotype and infection status.

Mitochondrial Genome Resource of the Cottony Ash Psyllid, a Host of a Newly Identified ‘Candidatus Liberibacter’ bacterium

Cottony ash psyllid (CAP, Phyllopsis discrepans) is an important, invasive insect pest of ash trees in North America where it has established populations and is the host of a newly identified strain of 'Candidatus Liberibacter solanacearum'. However, not much is known about the diversity of its introduced population. In this study, a CAP mitochondrial genome (mitogenome) sequence was obtained from a collection in Saskatoon, Saskatchewan, Canada. The CAP mitogenome is a circular DNA of 18,824 bp, encoding 13 protein-coding genes, 21 transfer RNA genes, and 2 ribosomal RNA genes. BLAST search using the CAP mitogenome as query against GenBank sequence database showed the mitogenome of Euphyllura phillyreae (15,202 bp) was the most similar (Query Coverage = 77%; Percentage Identity = 78.90%). The CAP mitogenome is significantly different from other known psyllid mitogenomes with the presence of a 4,357 bp control region (CR). The mitogenome sequence will further genomic understand of CAP.

Hiding in plain sight: a widespread native perennial harbors diverse haplotypes of 'Candidatus Liberibacter solanacearum' and its potato psyllid vector.

The unculturable bacterium 'Candidatus Liberibacter solanacearum' (CLso) is responsible for a growing number of emerging crop diseases. However, we know little about the diversity and ecology of CLso and its psyllid vectors outside of agricultural systems, which limits our ability to manage crop disease and understand the impacts this pathogen may have on wild plants in natural ecosystems. In North America, CLso is transmitted to crops by the native potato psyllid (Bactericera cockerelli). But the geographic and host plant range of the potato psyllid and CLso beyond the borders of agriculture are not well understood. A recent study of historic herbarium specimens revealed that a unique haplotype of CLso was present infecting populations of the native perennial Solanum umbelliferum in California decades before CLso was first detected in crops. We hypothesized that this haplotype, and other potentially novel CLso variants, are still present in S. umbelliferum populations. To test this, we surveyed populations of S. umbelliferum in Southern California for CLso and potato psyllid vectors. We found multiple haplotypes of CLso and the potato psyllid associated with these populations, with none of these genetic variants having been previously reported in California crops. These results suggest that CLso and its psyllid vectors are much more widespread and diverse in North American natural plant communities than suggested by data collected solely from crops and weeds in agricultural fields. Further characterization of these apparently asymptomatic haplotypes will facilitate comparison with disease-causing variants and provide insights into the continued emergence and spread of CLso.

A Novel Interaction of Nesidiocoris tenuis (Hemiptera: Miridae) as a Biological Control Agent of Bactericera cockerelli (Hemiptera: Triozidae) in Potato.

Nesidiocoris tenuis (Hemiptera: Miridae) is a generalist predator commonly used to control the whitefly Bemisia tabaci in Europe. This mirid has been found and established in South Texas, where it was initially observed feeding on nymphs of the psyllid Bactericera cockerelli (Hemiptera: Triozidae) in open tomato fields. B. cockerelli is the vector of the fastidious bacterium "Candidatus Liberibacter solanacearum" that causes diseases in several solanaceous crops, including zebra chip (ZC) disease in potatoes. There is a need to better understand how this predator impacts the control of important crop pests, such as potato psyllids. We assessed the interactions between N. tenuis and B. cockerelli in three different environmental settings. First, we estimated the numeric response of N. tenuis preying on B. cockerelli under laboratory and greenhouse conditions. Second, we evaluated the predator-prey interaction under controlled field cage conditions. Then, we exposed N. tenuis under controlled field release conditions to the natural occurrence of B. cockerelli. Finally, we assessed the compatibility between the use of N. tenuis as a biological control agent in a field study and its impact on ZC disease incidence, severity in potato tubers, and potato yield. Laboratory and greenhouse experiments resulted in diverse types of functional model responses, including exponential and linear mathematical models. Our findings revealed a significant predation effect exerted by N. tenuis, resulting in a reduction of more than fourfold in the number of B. cockerelli nymphs per cage. Specifically, the nymphal population decreased from 21 ± 3.2 in the absence of N. tenuis to 5 ± 1.6 when N. tenuis was present. Furthermore, the combination of N. tenuis with a reduced insecticide program increased potato yields, but only reduced ZC tuber incidence in one of two potato cultivars evaluated, and in one season. Findings from these studies indicate that N. tenuis could be effective as a biological control agent for B. cockerelli in potato production in South Texas. This is the first report of N. tenuis preying on immature stages of any psyllid species.

Influence of ‘Candidatus Liberibacter solanacearum’ infection on carrot root weight in Germany

AbstractInfection with the bacterium ‘Candidatus Liberibacter solanacearum’ (Lso) is suspected to cause severe damage in carrot leading to high carrot weight loss. This study investigates three main aspects: (i) whether there is a reduction of carrot root weight under field conditions due to Lso infection; (ii) the correlation between Lso infection rate in carrot plants and occurrence of the psyllid Trioza apicalis as the known vector for Lso in carrot, and (iii) the comparison between symptoms described in literature and observed symptoms associated with Lso infection. Therefore, field surveys were conducted from 2018 to 2021 on organically managed carrot fields in Lower Saxony, Germany. Two Rebell orange sticky traps were placed per field replaced on a weekly basis. Captured T. apicalis were morphologically identified and counted. Carrot plant samples were collected from T. apicalis infested fields. Discolouration of foliage and further symptoms on carrots were investigated. For detection of Lso in carrot plants and psyllids, the samples were analysed using PCR. The infection rate of carrot plants varied between 2.5% and 80% per field with low abundance of T. apicalis. Of the asymptomatic plants, 39.4% were infected with Lso, while 80.9% of the symptomatic plants were infected with Lso. The weight of Lso-positive carrot samples was not significantly reduced compared to Lso-negative samples. No economically relevant losses of carrot yield were reported by farmers participating in this study. This indicates that there was no effect of Lso infection on carrot root weight during this study. Of the symptoms associated with a Lso infection in carrots, only leaf discolouration could be confirmed. Overall, the bacterium is present in organically grown carrot plants in Lower Saxony but no major carrot root weight losses were observed.

First Report of the Association of the Psyllid Vector Bactericera trigonica (Hemiptera: Triozidae) with 'Candidatus Liberibacter Solanacearum' in Italy.

Psyllids, members of the family Triozidae, represent a potential threat to the cultivation of solanaceous and apiaceous crops worldwide, mainly as vectors of the phloem-restricted bacterium 'Candidatus Liberibacter solanacearum' (Lso). The Lso haplotypes C, D and E are known to affect apiaceous crops, such as carrot and celery, in several European countries. In Italy, data on the incidence and natural spread of both Lso and psyllids have not been reported so far. In this study, the presence of the vectors was investigated in a main Italian district for carrot production, the "Altopiano del Fucino" area (Central Italy). Both occasional and regular surveys were carried out on a total of five carrot fields and one potato field in 2021 and 2022. Bactericera trigonica (Hodkinson), which is known to efficiently transmit Lso to carrots, was found to be well-established in the area. High levels of population density were recorded in the summer period (more than 100 adult specimens per trap caught every two weeks) and then sharply decreased after the carrot harvest, confirming the strict association of this psyllid species with crop availability. In 2022, 27.5% of the total tested psyllid samples resulted in being positive for Lso haplotypes D and E, the latter being prevalent. This survey revealed, for the first time in Italy, the presence of B. trigonica adults associated with Lso in carrot crops. Although this study was limited to a few fields located in one area, it provided important evidence of the risks for Lso outbreaks and prompted further research to assess the spread and incidence of the disease in apiaceous cultivations in Italy.

Sub-optimal temperatures lead to altered expression of stress-related genes and increased 'Candidatus Liberibacter solanacearum' accumulation in potato psyllid.

The potato psyllid Bactericera cockerelli is the insect vector of the fastidious bacterium 'Candidatus Liberibacter solanacearum'. The bacterium infects both B. cockerelli and plant species, causing zebra chip (ZC) disease of potato and vein-greening disease of tomato. Temperatures are known to influence the initiation and progression of disease symptom in the host plant, and seasonal transitions from moderate to high temperatures trigger psyllid dispersal migration to facilitate survival. 'Ca. L. solanacearum' -infected and uninfected psyllids were reared at previously established 'permissible', optimal, and 'non-permissible' and temperatures of 18°C, 24°C, and 30°C, respectively. Gene expression profiles for 'Ca. L. solanacearum'-infected and -uninfected adult psyllids reared at different temperatures were characterized by Illumina RNA-Seq analysis. Bacterial genome copy number was quantified by real-time quantitative-PCR (qPCR) amplification. Relative gene expression profiles varied in psyllids reared at the three experimental temperatures. Psyllids reared at 18°C and 30°C exhibited greater fold-change increased expression of stress- and 'Ca. L. solanacearum' invasion-related proteins. Quantification by qPCR of bacterial genome copy number revealed that 'Ca. L. solanacearum' accumulation was significantly lower in psyllids reared at 18°C and 30°C, compared to 24°C. Temperature is a key factor in the life history of potato psyllid and multiplication/accumulation of 'Ca. L. solanacearum' in both the plant and psyllid host, influences the expression of genes associated with thermal stress tolerance, among others, and may have been instrumental in driving the co-evolution of the pathosystem.

Physalis virginiana as a Wild Field Host of Bactericera cockerelli (Hemiptera: Triozidae) and 'Candidatus Liberibacter solanacearum'.

The potato/tomato psyllid, Bactericera cockerelli (Šulc), is among the most important pests of solanaceous crops as a vector of the pathogen 'Candidatus Liberibacter solanacearum' (Lso). Lso-infected psyllids often arrive in crop fields from various wild species of Solanaceae and Convolvulaceae, especially those that provide early-season hosts for the vector. Physalis species are perennial plants within the family Solanaceae with often broad geographical distributions that overlap those of B. cockerelli, yet the status of many Physalis species as hosts for B. cockerelli or Lso remains unknown. Our objective was to determine whether wild Physalis species that occur in the potato-growing region of Galeana, Nuevo León, Mexico, host B. cockerelli populations and whether they also are susceptible to Lso. Sampling was carried out in the potato-growing zone of Galeana, Nuevo León, Mexico, where unidentified Physalis spp. are common. In March to October 2021, a wild plant identified as Physalis virginiana was observed; eggs, nymphs, and adults of B. cockerelli were observed on these plants throughout the growing season, and nymphs completed development on these plants under laboratory conditions. Lso also was detected in 22 of the 93 (23.7%) wild P. virginiana plants using conventional PCR, while 13.3% of B. cockerelli adults that emerged from P. virginiana cuttings harbored the pathogen. This is the first report that P. virginiana is a host for B. cockerelli and for Lso. These results suggest that P. virginiana is a likely source of Lso-infected psyllids colonizing solanaceous crops in northeastern Mexico. The importance of P. virginiana and other wild hosts on the population dynamics of the vector and pathogen should be investigated to assist in pest management decision-making.

Accumulation and Transmission of 'Candidatus Liberibacter solanacearum' Haplotypes by the Nymphs of Two Psyllid Vectors.

'Candidatus Liberibacter solanacearum' (Lso) is a plant pathogenic bacterium transmitted by psyllids that causes significant agricultural damage. Several Lso haplotypes have been reported. Among them, LsoA and LsoB are transmitted by the potato psyllid Bactericera cockerelli and infect solanaceous crops, and LsoD is transmitted by the carrot psyllid B. trigonica and infects apiaceous crops. Several studies evaluated the transmission of these haplotypes by adult psyllids. However, fewer data are available on the transmission of different Lso haplotypes by psyllid nymphs. In this study, we investigated the transmission of these three haplotypes by psyllid nymphs to expand our basic understanding of Lso transmission. Specifically, the objective was to determine if the haplotypes differed in their transmission rates by nymphs and if LsoA and LsoB accumulated at different rates in the guts of nymphs as it occurs in adults. First, we quantified LsoA and LsoB titers in the guts of third- and fifth-instar potato psyllid nymphs. We found similar LsoA titers in the two nymphal stages, while LsoB titer was lower in the gut of the third-instar nymphs compared to fifth-instar nymphs. Second, we assessed the transmission efficiency of LsoA and LsoB by third-instar nymphs to tomato plants, revealing that LsoA was transmitted earlier and with higher efficiency than LsoB. Finally, we examined the transmission of LsoD by carrot psyllid nymphs to celery plants and demonstrated an age-related difference in the transmission rate. These findings provide valuable insights into the transmission dynamics of different Lso haplotypes by nymphal vectors, shedding light on their epidemiology and interactions with their psyllid vectors.

RNA interference-mediated knockdown of genes involved in sugar transport and metabolism disrupts psyllid Bactericera cockerelli (Order: Hemiptera) gut physiology and results in high mortality.

The causal agent of zebra chip of potato and vein-greening diseases of tomato is "Candidatus Liberibacter solanacearum" (CLso), a fastidious bacterium transmitted by the potato psyllid. In the absence of disease-resistant cultivars, disease management has relied on minimizing vector population size to reduce CLso transmission, which requires frequent insecticide applications. There is growing interest in the use of RNA interference (RNAi) technology to supplant traditional insecticides with biopesticides. This requires knowledge of genes essential for insect livelihood whose knockdown leads to significant mortality or other phenotypes. Such candidate genes can be evaluated by reverse genetics approaches to further corroborate predicted gene function. Here, five potato psyllid genes involved in sugar homeostasis in the potato psyllid gut, α-glucosidase1 (AGLU1), aquaporin2 (AQP2), facilitated trehalose transporter1 (TRET1), Trehalase1 (TRE1), and Trehalase2 (TRE2), were investigated as candidates for effective gene silencing. Potato psyllid dsRNAs were designed to optimize knockdown of gene targets. Third instar PoP nymphs were given a 48-hr ingestion-access period (IAP) on individual or groups of dsRNA in 20% sucrose. Mortality was recorded 0, 3, 5, 7, and 9 days post-IAP. Gene knockdown was analyzed 9 days post-IAP by quantitative real-time reverse-transcriptase polymerase chain reaction amplification. The individual or stacked dsRNA combinations resulted in 20-60% and 20-40% knockdown, respectively, while subsequent psyllid mortality ranged from 20-40% to >60% for single and stacked dsRNA combinations, respectively. Reverse genetics analysis showed that simultaneous knockdown of the five selected candidate genes with predicted functions in pathways involved in sugar-homeostasis, metabolism, and -transport yielded the highest mortality, when compared with single or combinations of targets. Results confirmed the functions afforded by psyllid gut genes responsible for osmotic homeostasis and sugar metabolism/transport are essential for livelihood, identifying them as potentially lucrative RNAi biopesticide targets and highlighted the translational relevance of targeting multiple nodes in a physiological pathway simultaneously.

The plant pathogenic bacterium Candidatus Liberibacter solanacearum induces calcium-regulated autophagy in midgut cells of its insect vector Bactericera trigonica.

Autophagy plays an important role against pathogen infection in many organisms; however, little has been done with regard to vector-borne plant and animal pathogens, that sometimes replicate and cause deleterious effects in their vectors. Candidatus Liberibacter solanacearum (CLso) is a fastidious gram-negative phloem-restricted plant pathogen and vectored by the carrot psyllid, Bactericera trigonica. The plant disease caused by this bacterium is called carrot yellows and has recently gained much importance due to worldwide excessive economical losses. Here, we demonstrate that calcium ATPase, cytosolic calcium, and most importantly Beclin-1 have a role in regulating autophagy and its association with Liberibacter inside the psyllid. The presence of CLso generates reactive oxygen species and induces the expression of detoxification enzymes in the psyllid midguts, a main site for bacteria transmission. CLso also induces the expression of both sarco/endoplasmic reticulum Ca2+pump (SERCA) and 1,4,5-trisphosphate receptors (ITPR) in midguts, resulting in high levels of calcium in the cellular cytosol. Silencing these genes individually disrupted the calcium levels in the cytosol and resulted in direct effects on autophagy and subsequently on Liberibacter persistence and transmission. Inhibiting Beclin1-phosphorylation through different calcium-induced kinases altered the expression of autophagy and CLso titers and persistence. Based on our results obtained from the midgut, we suggest the existence of a direct correlation between cytosolic calcium levels, autophagy, and CLso persistence and transmission by the carrot psyllid. IMPORTANCE Plant diseases caused by vector-borne Liberibacter species are responsible for the most important economic losses in many agricultural sectors. Preventing these diseases relies mostly on chemical sprays against the insect vectors. Knowledge-based interference with the bacteria-vector interaction remains a promising approach as a sustainable solution. For unravelling how Liberibacter exploits molecular pathways in its insect vector for transmission, here, we show that the bacterium manipulates calcium levels on both sides of the endoplasmic reticulum membrane, resulting in manipulating autophagy. Silencing genes associated with these pathways disrupted the calcium levels in the cytosol and resulted in direct effects on autophagy and Liberibacter transmission. These results demonstrate major pathways that could be exploited for manipulating and controlling the disease transmission.

A 'Candidatus Liberibacter solanacearum' Haplotype B-Specific Family of Candidate Bacterial Effectors.

'Candidatus Liberibacter solanacearum' (Lso) is a phloem-limited pathogen associated with devastating diseases in members of the Solanaceae and Apiaceae and vectored by several psyllid species. Different Lso haplotypes have been identified, and LsoA and LsoB are responsible for diseases in Solanaceae crops. Our efforts are aimed at identifying pathogenicity factors used by this bacterium to thrive in different hosts. Bacterial secreted proteins can play a role in host colonization or the manipulation of the host immune responses; these proteins are called effectors. In this study, we identified six LsoB-specific proteins with a conserved secretion motif as well as a conserved N-terminal domain in the mature protein. These proteins had different expression and secretion patterns but a similar subcellular localization in Nicotiana benthamiana leaves, suggesting that they play different roles regardless of their conserved secretion motif. One of these proteins, CKC_04425, was expressed at high levels in the insect vector and the host plant, indicating that it could play a role in both the plant and insect hosts, whereas the others were mainly expressed in the plant. One protein, CKC_05701, was able to efficiently suppress programmed cell death and reactive oxygen species production, suggesting that it may have a virulence role in LsoB-specific pathogenesis.

Biology, Ecology, and Management of the Potato Psyllid, Bactericera cockerelli (Hemiptera: Triozidae), and Zebra Chip Disease in Potato.

The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), transmits the pathogen "Candidatus liberibacter solanacearum" (Lso), the putative causal agent of zebra chip disease (ZC). ZC is a disease of potato that reduces yield and quality and has disrupted integrated pest management programs in parts of the Americas and New Zealand. Advances in our understanding of the ecological factors that influence ZC epidemiology have been accelerated by the relatively recent identification of Lso and motivated by the steady increase in ZC distribution and the potential for devastating economic losses on a global scale. Management of ZC remains heavily reliant upon insecticides, which is not sustainable from the standpoint of insecticide resistance, nontarget effects on natural enemies, and regulations that may limit such tools. This review synthesizes the literature on potato psyllids and ZC, outlining recent progress, identifying knowledge gaps, and proposing avenues for further research on this important pathosystem of potatoes.

Current and future potential geographical distribution of Bactericera cockerelli: an invasive pest of increasing global importance

AbstractDue to ongoing climate change and the spread of invasive pests, understanding and predicting climatic suitability for invasive insect species has shown growing demand from government and industry biosecurity managers. The invasive pest Bactericera cockerelli, (Šulc) (Hemiptera: Triozidae), commonly known as tomato potato psyllid (TPP), is native to North America and has recently invaded Australasia. TPP is also the vector of the bacterial plant pathogen Candidatus Liberibacter solanacearum (CLso), which has caused severe economic losses for potato growers worldwide. We used the niche modelling software CLIMEX to predict the potential geographical distribution of TPP in Australasia and worldwide under current and future climatic scenarios. Our model prediction of the current climate conditions closely agrees with all the known distributions of TPP. In its native range (North America), TPP is predicted to expand its current geographical range in semi‐arid, temperate, and continental climates. Within Australia, along with the known occurrence of TPP in Western Australia, potential expansion into South Australia, Victoria, New South Wales and Queensland is predicted. The predicted distribution closely matches all the known records with higher climatic suitability in New Zealand. Globally, the model projected that the pest‐free countries in Europe and East Asia are climatically more suitable for TPP. Predictions under the future climate change scenarios (A1B, CSIRO Mk 3.0 for 2090) showed a significant reduction of the known geographical range of TPP with a possible expansion towards higher latitudes. Areas in North America and Australia are projected to be less climatically suitable for the survival of TPP in future climates. However, our model suggested that Europe and New Zealand will remain unchanged or will become more favourable in the future. These CLIMEX projections for current and future climatic distribution provide valuable information for existing and future biosecurity preparedness and management programmes, which may prove helpful in risk assessments and identifying potential areas that are likely to be susceptible to a TPP invasion.

Acquisition and transmission of "Candidatus Liberibacter solanacearum" differs among Wolbachia-infected and -uninfected haplotypes of Bactericera cockerelli.

"Candidatus Liberibacter solanacearum" (Lso) causes disease symptoms and economic losses in potato, tomato, and other solanaceous crops in North America. Lso is transmitted to plants by potato psyllid, Bactericera cockerelli, which occurs as distinct haplotypes named western, central, and northwestern that differ in presence or absence of the bacterial endosymbiont, Wolbachia. Previous work showed that all three vector haplotypes can transmit Lso, but it was not clear whether acquisition and transmission rates of Lso were equal among the haplotypes. The goal of our study was to compare Lso infection rates among psyllids of the western, central, and northwestern haplotypes. Using data collected from several years of periodic testing of Lso infection of laboratory-reared potato psyllid colonies, we showed that psyllids of the western and central haplotypes are more likely to harbor Lso than are psyllids of the northwestern haplotype. We then used greenhouse assays to demonstrate that psyllids of the northwestern haplotype are less likely to acquire and transmit Lso compared with those of the western haplotype. Lso infection rates corresponded with Wolbachia infection among the three psyllid haplotypes. The Wolbachia-infected central and western haplotypes were more likely to harbor and transmit Lso compared with the Wolbachia-free northwestern haplotype. Results demonstrate that potato psyllids of the western and central haplotypes pose a greater risk for spread of Lso in crops and suggest a pattern between infection with Lso and Wolbachia in potato psyllid.

Metabolic changes and potential biomarkers in "Candidatus Liberibacter solanacearum"-infected potato psyllids: implications for psyllid-pathogen interactions.

Psyllid yellows, vein-greening (VG), and zebra chip (ZC) diseases, which are primarily transmitted by potato psyllid (PoP) carrying Candidatus Liberibacter solanacearum (CLso), have caused significant losses in solanaceous crop production worldwide. Pathogens interact with their vectors at the organic and cellular levels, while the potential changes that may occur at the biochemical level are less well reported. In this study, the impact of CLso on the metabolism of PoP and the identification of biomarkers from infected psyllids were examined. Using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) analysis, metabolomic changes in CLso-infected psyllids were compared to uninfected ones. A total of 34 metabolites were identified as potential biomarkers of CLso infection, which were primarily related to amino acid, carbohydrate, and lipid metabolism. The significant increase in glycerophospholipids is thought to be associated with CLso evading the insect vector's immune defense. Matrix-assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI-MSI) was used to map the spatial distribution of these biomarkers, revealing that 15-keto-Prostaglandin E2 and alpha-D-Glucose were highly expressed in the abdomen of uninfected psyllids but down-regulated in infected psyllids. It is speculated that this down-regulation may be due to CLso evading surveillance by immune suppression in the PoP midgut. Overall, valuable biochemical information was provided, a theoretical basis for a better understanding of psyllid-pathogen interactions was offered, and the findings may aid in breaking the transmission cycle of these diseases.

An Overview of the Emergence of Plant Pathogen 'Candidatus Liberibacter solanacearum' in Europe.

In this paper, a comprehensive overview of the 'Candidatus Liberibacter solanacearum' presence in Europe was provided. The analyzed findings revealed that, since the first appearance of this pathogen in Finland and Spain in 2008, it has spread to 13 new European countries. Therefore, 'Ca. L. solanacearum' has spread very quickly across the European continent, as evident from the emergence of new host plants within the Apiaceae, Urticaceae, and Polygonaceae families, as well as new haplotypes of this pathogen. Thus far, 5 of the 15 'Ca. L. solanacearum' haplotypes determined across the globe have been confirmed in Europe (haplotypes C, D, E, U, and H). Fully competent 'Ca. L. solanacearum' vectors include Bactericera cockerelli, Trioza apicalis, and B. trigonica; however, only T. apicalis and B. trigonica are presently established in Europe and are very important for plants from the Apiaceae family in particular. Moreover, psyllid species such as B. tremblayi, T. urticae, and T. anthrisci have also been confirmed positive for 'Ca. L. solanacearum'. Constant monitoring of its spread in the field (in both symptomatic and asymptomatic plants), use of sensitive molecular diagnostic techniques, and application of timely management strategies are, therefore, of utmost importance for the control of this destructive pathogen.

Potato psyllids mount distinct gut responses against two different 'Candidatus Liberibacter solanacearum' haplotypes.

'Candidatus Liberibacter solanacearum' (Lso) is a bacterial pathogen infecting several crops and causing damaging diseases. Several Lso haplotypes have been identified. Among the seven haplotypes present in North America, LsoA and LsoB are transmitted by the potato psyllid, Bactericera cockerelli (Šulc), in a circulative and persistent manner. The gut, which is the first organ pathogen encounters, could be a barrier for Lso transmission. However, the molecular interactions between Lso and the psyllid vector at the gut interface remain largely unknown. In this study, we investigated the global transcriptional responses of the adult psyllid gut upon infection with two Lso haplotypes (LsoA and LsoB) using Illumina sequencing. The results showed that each haplotype triggers a unique transcriptional response, with most of the distinct genes elicited by the highly virulent LsoB. The differentially expressed genes were mainly associated with digestion and metabolism, stress response, immunity, detoxification as well as cell proliferation and epithelium renewal. Importantly, distinct immune pathways were triggered by LsoA and LsoB in the gut of the potato psyllid. The information in this study will provide an understanding of the molecular basis of the interactions between the potato psyllid gut and Lso, which may lead to the discovery of novel molecular targets for the control of these pathogens.

Development of a Loop-Mediated Isothermal Amplification (LAMP) Method to Detect the Potato Zebra Chip Pathogen 'Candidatus Liberibacter solanacearum' (Lso) and Differentiate Haplotypes A and B.

'Candidatus Liberibacter solanacearum' (Lso) is the causal agent of zebra chip of potato (Solanum tuberosum), which can significantly reduce potato yield. In this study, a loop-mediated isothermal amplification (LAMP) method for the detection of Lso haplotypes A and B was developed and evaluated. Two sets of LAMP primers named LAMP-A and LAMP-B were designed and tested for specificity and sensitivity. Both LAMP-A and LAMP-B were specific to Lso in in silico analysis using the Primer-Blast tool. The LAMP-A and LAMP-B could only produce positive signals from DNA mixtures of Lso-infected tomato but not from the genomic DNA of 37 nontarget plant pathogens. The sensitivity of LAMP-A and LAMP-B on Lso haplotypes A and B were tested on gBlocks and genomic DNA from Lso-infected tomato. On the genomic DNA for LAMP-A, the lowest amount of template DNA for a positive LAMP reaction was 2 to 20 ng on four haplotype A strains and 20 to 80 ng on four haplotype B strains; for LAMP-B, the lowest amount of template DNA for a positive LAMP reaction was 0.02 to 2 ng on four haplotype B strains and 20 ng to no amplification on four haplotype A strains. On gBlocks for LAMP-A, the lowest number of copies for a positive LAMP reaction was 60 on haplotype A and 600 on haplotype B; for LAMP-B, the lowest number of copies for a positive LAMP reaction was 60 on haplotype B and 600 on haplotype A. Therefore, considering the convenience of the LAMP technique, as well as the high specificity and sensitivity, the LAMP-A and LAMP-B primers can be used together to test the probable Lso-infected plant or psyllid samples to rapidly, accurately, and directly differentiate haplotypes A and B. We highly recommend this LAMP system to plant pathology practitioners and diagnostic labs for routine detection of Lso and confirmation of zebra chip disease on potato or tomato.

Association of endoplasmic reticulum associated degradation (ERAD) with the transmission of Liberibacter solanacearum by its psyllid vector.

Candidatus Liberibacter solanacearum (CLso) is a complex of gram negative plant pathogenic and fastidious bacterial haplotypes restricted to the phloem and transmitted by several psyllid species. In Israel, the carrot psyllid Bactericera trigonica transmits CLso haplotype D in a persistent and propagative manner and causes the carrot yellows disease, inflicting significant economic losses in many countries. Understanding the transmission of CLso is fundamental to devising sustainable management strategies. Persistent transmission of vector-borne pathogens involves the critical steps of adhesion, cell invasion and replication inside the insect gut cells before passage to the hemolymph. Using microscopy and expression analyses, we have previously confirmed a role for the endoplasmic reticulum (ER) in inducing immune responses and subsequent molecular pathways resulting in programmed cell death (apoptosis) upon CLso-infection in the midgut. In the current study, we confirm that the ER-associated degradation (ERAD) machinery and its associated marker genes were upregulated in CLso infected insects, including Derlin-1, Selenoprotein-1 and Ubiquitin Ligase RNF-185. Silencing Derlin-1, which acts on the ER membrane by regulating the degradation of unfolded proteins upon ER stress, revealed its role in CLso persistence and transmission. Molecular pathways initiated in the ER membrane upon bacterial infection are well documented in human, animal and insect systems, and this study confirms the role of the ER in CLso-psyllid interactions.