Tamborindeguy, Cecilia

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 Liberibacter solanacearum” (Lso) is a phloem-limited bacterial pathogen transmitted by psyllid. In the USA, the haplotypes A and B are transmitted by the tomato psyllid, Bactericera cockerelli, and are responsible for economic damage to the solanaceous crop industry. In tomato, haplotypes A and B cause diseases with differing degrees of severity, yet their underlying mechanisms are not well understood. The role that abiotic stress plays in disease development has not been characterized. In the present study, we evaluated whether water stress influenced the development of symptoms associated with these haplotypes in tomato ( Solanum lycopersicum “Moneymaker”). First, pot-grown tomato plants were subjected to either a control or a water-stress regime, then they were assigned to one of three infection treatments (Lso-free, LsoA, or LsoB) under laboratory-controlled conditions. Symptom development was monitored for up to 8 weeks following infection. Results of this experiment revealed that water stress significantly reduced the plant water potential and was the primary driver of reduced height, with infection only having an effect in later weeks. Water stress also increased the detectability of Lso throughout the plant and across three timepoints (weeks 4, 6, and 8 after infection). This increase in Lso-positive tissues suggests that water stress creates a more homogenous distribution of Lso throughout the plant. More noticeably, water stress significantly reduced the severity of the disease associated with haplotype A but not B. Overall, these findings revealed the existence of haplotype-specific interactions between Lso infection and water stress on the tomato health. This work highlights the influence of abiotic factors on plant health.

Abstract ‘ Candidatus Liberibacter solanacearum’ (Lso) is a devastating bacterial pathogen of crops transmitted by psyllids. Previously, a link between changes in ubiquitination and the progression of diseases caused by Lso was established. Among the Lso haplotypes, LsoA and LsoB infect solanaceous crops. LsoA induces chlorosis and stunting in tomato, while LsoB infection leads to more severe symptoms, including plant death. To better characterize the molecular basis of the differences in the diseases caused by these haplotypes, we cataloged the ubiquitinome of tomato leaves four weeks after LsoA and LsoB-infection and following infestation with Lso-free psyllids. Our analysis revealed haplotype-specific changes in the plant ubiquitinome. Gene Ontology (GO) terms related to glucose metabolism and proteasome-mediated ubiquitin-dependent protein catabolism were enriched among the differentially ubiquitinated proteins between LsoA-infected and Lso-free infested plants. Additionally, a KEGG pathway analysis determined an overrepresentation of proteins involved in carbon metabolism and fixation via the Calvin cycle. In contrast, the comparison of LsoB-infected and Lso-free infested plants revealed a broader range of enriched GO terms and KEGG pathways, including those associated with carbohydrate and energy metabolism, proteasome activity, and oxidative stress. These results contribute to our understanding of the development of Liberibacter-related diseases and reveal the importance of ubiquitin-related pathways in Lso infection. They also contribute to the expanding inventory of ubiquitinated proteins.

ABSTRACT “ Candidatus Liberibacter solanacearum” (Lso) is a highly destructive plant pathogen within the alpha-proteobacteria group. Multiple Lso haplotypes occur worldwide, each uniquely associated with a specific psyllid vector. Haplotypes A and B, found in the United States, cause serious damage to solanaceous crops and are transmitted by Bactericera cockerelli , known as the potato psyllid in a circulative and persistent manner. The psyllid gut is the first organ encountered by Lso and may act as a barrier to its transmission; however, the immune response of the gut to Lso infection remains largely uncharacterized. In this study, we examined autophagic responses in the gut of potato psyllids at early, mid, and late infection stages. Based on gene expression analyses, microscopic observations, and Western blotting, we found no clear evidence of autophagy induction despite Lso infection. Nevertheless, during mid and late phases of LsoB infection, we observed downregulation of the mechanistic target of rapamycin and decreased accumulation of ATG8-II. Notably, inducing autophagy with rapamycin significantly reduced LsoA titers in the psyllid guts after a 5-day acquisition access period and lowered transmission efficiency, while LsoB remained unaffected. These findings suggest that modulating autophagy in the gut of potato psyllids could be a promising strategy to limit LsoA acquisition and transmission, while highlighting LsoA and LsoB possess distinct molecular regulatory mechanisms in the psyllid gut. IMPORTANCE Liberibacters are devastating plant pathogens transmitted by psyllids. Because these bacteria are fastidious, the study of the molecular mechanisms involved in plant infection and transmission is difficult. Here, we determined that inducing autophagy in the potato psyllid can affect the acquisition and transmission of Lso haplotype A but not haplotype B. Comparing the host and vector responses to different liberibacters can help identify their transmission and infection mechanisms and find targets to disrupt these processes.

‘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.

‘ 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.

‘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.

‘Candidatus Liberibacter solanacearum’ (Lso) is a phloem-limited bacterial plant pathogen infecting solanaceous plants in the Americas and New Zealand and is associated with diseases of apiaceous crops in Europe, Northern Africa, and the Middle East. This pathogen is also related to other Liberibacter species that infect other crops. In the USA, two haplotypes of Lso, LsoA and LsoB, are predominant and responsible for diseases in potato and tomato. Tobacco, Nicotiana tabacum, a model species to study plant defenses, is a host for Lso; therefore, the interaction between Lso and this host plant could be used to study Liberibacter−plant interactions. In this study, we characterized the infection associated with LsoA and LsoB in tobacco. Under laboratory conditions, LsoB caused more severe symptoms than LsoA, and LsoA and LsoB titers were dynamic during the 7 weeks of the experiment. We also measured SA and other metabolites, including oxylipins, at an early point of infection and found that SA was accumulated in plants infected with LsoB but not with LsoA; whereas ABA levels were reduced in LsoA- but not in LsoB-infected plants.

Abstract Background The tomato psyllid, Bactericera cockerelli Šulc (Hemiptera: Triozidae), is a pest of solanaceous crops such as tomato (Solanum lycopersicum L.) in the U.S. and vectors the disease-causing pathogen ‘Candidatus Liberibacter solanacearum’ (or Lso). Disease symptom severity is dependent on Lso haplotype: tomato plants infected with Lso haplotype B experience more severe symptoms and higher mortality compared to plants infected with Lso haplotype A. By characterizing the molecular differences in the tomato plant’s responses to Lso haplotypes, the key components of LsoB virulence can be identified and, thus, targeted for disease mitigation strategies. Results To characterize the tomato plant genes putatively involved in the differential immune responses to Lso haplotypes A and B, RNA was extracted from tomato ‘Moneymaker’ leaves 3 weeks after psyllid infestation. Gene expression levels were compared between uninfected tomato plants (i.e., controls and plants infested with Lso-free psyllids) and infected plants (i.e., plants infested with psyllids infected with either Lso haplotype A or Lso haplotype B). Furthermore, expression levels were compared between plants infected with Lso haplotype A and plants infected with Lso haplotype B. A whole transcriptome analysis identified 578 differentially expressed genes (DEGs) between uninfected and infected plants as well as 451 DEGs between LsoA- and LsoB-infected plants. These DEGs were primarily associated with plant defense against abiotic and biotic stressors, growth/development, plant primary metabolism, transport and signaling, and transcription/translation. These gene expression changes suggested that tomato plants traded off plant growth and homeostasis for improved defense against pathogens, especially when infected with LsoB. Consistent with these results, tomato plant growth experiments determined that LsoB-infected plants were significantly stunted and had impaired negative geotropism. However, it appeared that the defense responses mounted by tomatoes were insufficient for overcoming the disease symptoms and mortality caused by LsoB infection, while these defenses could compensate for LsoA infection. Conclusion The transcriptomic analysis and growth experiments demonstrated that Lso-infected tomato plants underwent gene expression changes related to abiotic and biotic stressors, impaired growth/development, impaired plant primary metabolism, impaired transport and signaling transduction, and impaired transcription/translation. Furthermore, the transcriptomic analysis also showed that LsoB-infected plants, relative to LsoA-infected, experienced more severe stunting, had improved responses to some stressors and impaired responses to others, had poorer transport and signaling transduction, and had impaired carbohydrate synthesis and photosynthesis.