Publications

4476

IntroductionCandidatus Liberibacter solanacearum (CLso) is a regulated plant pathogen in European and some Asian countries, associated with severe diseases in economically important Apiaceous and Solanaceous crops, including potato, tomato, and carrot. Eleven haplotypes of CLso have been identified based on the difference in rRNA and conserved genes and host and pathogenicity. Although it is pathogenic to a wide range of plants, the mechanisms of plant response and functional decline of host plants are not well defined. This study aims to describe the underlying mechanism of the functional decline of tomato plants infected by CLso by analyzing the transcriptomic response of tomato plants to CLso haplotypes A and B.MethodsNext-generation sequencing (NGS) data were generated from total RNA of tomato plants infected by CLso haplotypes A and B, and uninfected tomato plants, while qPCR analysis was used to validate the in-silico expression analysis. Gene Ontology and KEGG pathways were enriched using differentially expressed genes.ResultsPlants infected with CLso haplotype B saw 229 genes upregulated when compared to uninfected plants, while 1,135 were downregulated. Healthy tomato plants and plants infected by haplotype A had similar expression levels, which is consistent with the fact that CLso haplotype A does not show apparent symptoms in tomato plants. Photosynthesis and starch biosynthesis were impaired while starch amylolysis was promoted in plants infected by CLso haplotype B compared with uninfected plants. The changes in pathway gene expression suggest that carbohydrate consumption in infected plants was more extensive than accumulation. In addition, cell-wall-related genes, including steroid biosynthesis pathways, were downregulated in plants infected with CLso haplotype B suggesting a reduction in membrane fluidity, cell signaling, and defense against bacteria. In addition, genes in phenylpropanoid metabolism and DNA replication were generally suppressed by CLso infection, affecting plant growth and defense.DiscussionThis study provides insights into plants’ defense and functional decline due to pathogenic CLso using whole transcriptome sequencing and qPCR validation. Our results show how tomato plants react in metabolic pathways during the deterioration caused by pathogenic CLso. Understanding the underlying mechanisms can enhance disease control and create opportunities for breeding resistant or tolerant varieties.

<p><strong>Background.</strong> Climate change models have projected an increase in the distribution of certain crop pests of economic importance by forecasting more favorable future conditions for these organisms. In citrus farming, Huanglongbing is one of the most devastating diseases worldwide, since it has caused the death of millions of trees. <strong>Objetive.</strong> The objective of this study was to estimate the current and future distribution of <em>Candidatus </em>Liberibacter asiaticus in Mexico, under the climate change scenarios SSP2 4.5 and SSP5 8.5, for the years 2050 and 2070. <strong>Methodology.</strong> Distribution models were generated with MaxEnt and R, using uncorrelated bioclimatic variables from eight General Circulation Models (GCM) derived from CMIP6 and disease presence data. <strong>Results.</strong> The results indicate that the current suitability is 44.6 %. The future distribution depended on how model predictions were pooled. An optimistic approach that considered the intersection of all models showed a small reduction of 4.1% while, considering the union of all the GCM models, the increase will vary from 12.3 to 20.1 % of the Mexican territory depending on the particular scenario and time projection. <strong>Implications.</strong> The zones of potential occurrence of <em>Candidatus </em>Liberibacter asiaticus include most of the citrus-growing areas in Mexico. <strong>Conclusion. </strong>In some regions, future scenarios show a reduction in the potential occurrence of the species in citrus plantations. However, the risk remains because its surroundings include suitable areas that can be sources of dissemination of the disease. </p>

‘CandidatusPhytoplasma ulmi’ (Ca.P. ulmi) belongs to the ribosomal subgroup 16SrV-A and is associated with dieback, shoot proliferation and yellows disease on variousUlmusspp. Other plant species, such asCarpinus betulusandPrunusspp. have also been reported infected by the same pathogen. In 2021, in the frame of research activities focused on grapevine’s Flavescence dorée (FD), one specimen ofOrientus ishidae- an East Palearctic leafhopper that was identified as an alternative vector of FD phytoplasmas - was found harboringCa.P. ulmi in southern Switzerland. No phytoplasmas were detected in plant samples taken in the same location.Orientus ishidaehas already been reported to be able to acquire diverse phytoplasmas associated with other plant diseases, such as Peach X-disease. This is the first report ofCa.P. ulmi in Switzerland, as well as inO. ishidae.Ca.P. ulmi may potentially be present in the wild compartment of the Swiss Pre-alpine and Alpine range, but no dedicated survey has so far been conducted. In the case ofO. ishidae, this finding highlights the broad affinity of such a species for the acquisition of several phytoplasmas. This calls for a further investigation regarding its potential role as a vector on various pathosystems of agronomic importance.

The increasing impact of phloem-restricted bacteria on economically important crops has led to renewed interest in understanding the pathogenesis at the genomic and histological levels of these diseases. The genus Candidatus Liberibacter is associated with economically devastating diseases, highlighting Candidatus Liberibacter asiaticus (CLas) and Candidatus Liberibacter solanaceraum (CLso) in citrus and vegetables. Plant-pathogen interaction studies are limited due to the non-culturable nature of the pathogenic species of the genus Ca. Liberibacter, as well as the lack of experimental models. The objective of this work was to implement a model for the study of bacteria of the genus Candidatus Liberibacter, using tomato-CLso as an experimental model. Through a time course analysis of the tomato-CLso infective process, it was determined that there is a direct correlation between the bacterial load and symptom development, differentiated into early, intermediate and late stages. Additionally, a comparative transcriptional analysis of antibacterial defense marker genes (PR-P1, miR160, and miR393) determined that the response of these genes in the tomato-CLso and lime-CLas pathosystems are equivalent. Our results demonstrate that the tomato-CLso system represents an important model for the study of the interaction between plants and non-cultivable phloem restricted bacteria.

Insect–microbe endosymbiotic associations are omnipresent in nature, wherein the symbiotic microbes often play pivotal biological roles for their host insects. In particular, insects utilizing nutritionally imbalanced food sources are dependent on specific microbial symbionts to compensate for the nutritional deficiency via provisioning of B vitamins in blood-feeding insects, such as tsetse flies, lice, and bedbugs. Bat flies of the family Nycteribiidae (Diptera) are blood-sucking ectoparasites of bats and shown to be associated with co-speciating bacterial endosymbiont “Candidatus Aschnera chinzeii,” although functional aspects of the microbial symbiosis have been totally unknown. In this study, we report the first complete genome sequence of Aschnera from the bristled bat fly Penicillidia jenynsii. The Aschnera genome consisted of a 748,020 bp circular chromosome and a 18,747 bp circular plasmid. The chromosome encoded 603 protein coding genes (including 3 pseudogenes), 33 transfer RNAs, and 1 copy of 16S/23S/5S ribosomal RNA operon. The plasmid contained 10 protein coding genes, whose biological function was elusive. The genome size, 0.77 Mbp, was drastically reduced in comparison with 4–6 Mbp genomes of free-living γ-proteobacteria. Accordingly, the Aschnera genome was devoid of many important functional genes, such as synthetic pathway genes for purines, pyrimidines, and essential amino acids. On the other hand, the Aschnera genome retained complete or near-complete synthetic pathway genes for biotin (vitamin B7), tetrahydrofolate (vitamin B9), riboflavin (vitamin B2), and pyridoxal 5'-phosphate (vitamin B6), suggesting that Aschnera provides these vitamins and cofactors that are deficient in the blood meal of the host bat fly. Similar retention patterns of the synthetic pathway genes for vitamins and cofactors were also observed in the endosymbiont genomes of other blood-sucking insects, such as Riesia of human lice, Arsenophonus of louse flies, and Wigglesworthia of tsetse flies, which may be either due to convergent evolution in the blood-sucking host insects or reflecting the genomic architecture of Arsenophonus-allied bacteria.