Biology subjects

Levy, A.

Publications and source records attributed to Levy, A..

At least 37 records · Page 2Linked to original sources

bioRxiv2025

Neural correlates of boundary extension during visual imagination

People typically remember seeing a greater expanse of a scene than was visible in a studied close-up (boundary extension, BE). Multivoxel pattern analysis was used to test the neural correlates of BE. Classifiers were trained using a whole-brain searchlight method to discriminate between close-up and wider-angle versions of 16 scenes during repeated perceptual exposures. Earlier, each subject studied either the close or wide version of each scene and then visually imagined it from memory. If a brain region reflects BE, then unlike classification during perception, visual images of close views should sometimes be misclassified as wide (capturing false memory beyond the view), whereas visual images of wide views should be correctly classified. BE-consistent patterns during imagery were found in high-level visual regions, including posterior superior parietal cortex. This pattern did not reflect a brain-wide bias toward better classification of wider-angle views: the pattern reversed (better classification of close views) in the early visual cortex, presenting a novel distinction between early and late visual representations in imagery. We propose that this method reflects active maintenance of boundary-extended scene representations in memory and that it holds promise as a general purpose tool for decoding false memory in the brain.

neuroscience↗

bioRxiv2024

Plasmids, Prophages and Defense Systems are Depleted from Plant Microbiota Genomes

Plant-associated bacteria significantly impact plant growth and health. Understanding how bacterial genomes adapt to plants can provide insights into their growth promotion and virulence functions. Here, we compared 38,912 bacterial genomes and 6,073 metagenomes to explore the distribution of mobile genetic elements and defense systems in plant-associated bacteria. We reveal a consistent taxon-independent depletion of prophages, plasmids, and defense systems in plant-associated bacteria, particularly in the phyllosphere, compared to other ecosystems. The mobilome depletion suggests the presence of unique ecological constraints or molecular mechanisms exerted by plants to control the bacterial mobilomes independently of the bacterial defense.

bioinformatics↗

bioRxiv2024

Chlorobaculum tepidum Outer Membrane Vesicles Are Likely a Significant Route for Biogenic Sulfur Transport.

Outer membrane-derived vesicles (OMVs) have been studied in different phyla of Gramnegative bacteria, most extensively in the Pseudomonadota, where they have been shown to participate in diverse biological and environmental processes. To date, the production of OMVs has not been reported in the Chlorobiaceae within the phylum Chlorobiota. Chlorobaculum. tepidum is the model organism for the Chlorobiaceae that synthesizes and consumes insoluble extracellular sulfur (S(0)) globules by an unknown mechanism. Here, we report evidence implicating outer membrane vesicles in biogenic S(0) globule synthesis. We demonstrate that Cba. tepidum secretes OMVs in the extracellular milieu, and that OMV concentration and size vary with growth conditions, particularly sulfide concentration. A core of 31 proteins involved in diverse biological processes such as cell wall biogenesis, inorganic ion transport and metabolism were found to be shared between OMVs, extracellular S(0) globules and Cba. tepidum intact cells. Multiple analytical methods indicated that OMVs contain S(0) and that OMVs and biogenic S(0) globules share protein and polysaccharide signatures, including lipooligosaccharides. Together these lines of evidence indicate that Cba. tepidums OMVs are one component of sulfur transport between cells and extracellular sulfur globules. IMPORTANCEAll living cells must exchange material with their environment while maintaining cellular integrity. This is a particular challenge for materials that are not water soluble, yet many bacteria utilize insoluble materials for energy conservation and as nutrients for growth. Here we show that Cba. tepidum makes outer membrane vesicles and that these vesicles are likely involved in the exchange of material with extracellular elemental sulfur globules formed and consumed by Cba. tepidum as part of its energy metabolism based on oxidizing reduced sulfur compounds like hydrogen sulfide. These data expand our basic understanding of Cba. tepidums metabolism. As elemental sulfur is an industrial by-product with a limited number of uses, the information here may help enable the use of additional sulfur compounds by Cba. tepidum to drive the synthesis of biomass and/or specialty biochemicals from waste elemental sulfur by this autotrophic bacterium.

microbiology↗

bioRxiv2024

Transcriptomic profiling of Candidatus Liberibacter asiaticus in different citrus tissues reveals novel insights into Huanglongbing pathogenesis

Candidatus Liberibacter asiaticus (Las) is a gram-negative bacterial pathogen associated with citrus huanglongbing (HLB) or greening disease. Las is transmitted by the Asian citrus psyllid (ACP) where it colonizes the phloem tissue, resulting in substantial economic losses to citrus industry worldwide. Despite extensive efforts, effective management strategies against HLB remain elusive, necessitating a deeper understanding of the pathogen s biology. Las undergoes cell-to-cell movement through phloem flow and colonizes different tissues in which Las may have varying interactions with the host. Here, we investigate the transcriptomic landscape of Las in citrus seed coat vasculatures, enabling a complete gene expression profiling of Las genome and revealing unique transcriptomic patterns compared to previous studies using midrib tissues. Comparative transcriptomics between seed coat, midrib and ACP identified specific responses and metabolic states of Las in different host tissue. Two Las virulence factors that exhibit higher expression in seed coat can suppress callose deposition. Therefore, they may contribute to unclogging sieve plate pores during Las colonization in seed coat vasculature. Furthermore, analysis of regulatory elements uncovers a potential role of LuxR-type transcription factors in regulating Liberibacter effector gene expression during plant colonization. Together, this work provides novel insights into the pathogenesis of the devastating citrus HLB. FundingThis work is supported by USDA National Institute of Food and Agriculture award No. 2020-70029-33197 to W.M and A.L.

microbiology↗

bioRxiv2024

Revealing biomolecular structure and motion with neural ab initio cryo-EM reconstruction

Proteins and other biomolecules form dynamic macromolecular machines that are tightly orchestrated to move, bind, and perform chemistry. Cryo-electron microscopy (cryo-EM) and cryo-electron tomography (cryo-ET) can access the intrinsic heterogeneity of these complexes and are therefore key tools for understanding their function. However, 3D reconstruction of the collected imaging data presents a challenging computational problem, especially without any starting information, a setting termed ab initio reconstruction. Here, we introduce cryoDRGN-AI, a method leveraging an expressive neural representation and combining an exhaustive search strategy with gradient-based optimization to process challenging heterogeneous datasets. Using cryoDRGN-AI, we reveal new conformational states in large datasets, reconstruct previously unresolved motions from unfiltered datasets, and demonstrate ab initio reconstruction of biomolecular complexes from in situ data. With this expressive and scalable model for structure determination, we hope to unlock the full potential of cryo-EM and cryo-ET as a high-throughput tool for structural biology and discovery.

biophysics↗

bioRxiv2024

Towards Interpretable Cryo-EM: Disentangling Latent Spaces of Molecular Conformations

Molecules are essential building blocks of life and their different conformations (i.e., shapes) crucially determine the functional role that they play in living organisms. Cryogenic Electron Microscopy (cryo-EM) allows for acquisition of large image datasets of individual molecules. Recent advances in computational cryo-EM have made it possible to learn latent variable models of conformation landscapes. However, interpreting these latent spaces remains a challenge as their individual dimensions are often arbitrary. The key message of our work is that this interpretation challenge can be viewed as an Independent Component Analysis (ICA) problem where we seek models that have the property of identifiability. That means, they have an essentially unique solution, representing a conformational latent space that separates the different degrees of freedom a molecule is equipped with in nature. Thus, we aim to advance the computational field of cryo-EM beyond visualizations as we connect it with the theoretical framework of (nonlinear) ICA and discuss the need for identifiable models, improved metrics, and benchmarks. Moving forward, we propose future directions for enhancing the disentanglement of latent spaces in cryo-EM, refining evaluation metrics and exploring techniques that leverage physics-based decoders of biomolecular systems. Moreover, we discuss how future technological developments in time-resolved single particle imaging may enable the application of nonlinear ICA models that can discover the true conformation changes of molecules in nature. The pursuit of interpretable conformational latent spaces will empower researchers to unravel complex biological processes and facilitate targeted interventions. This has significant implications for drug discovery and structural biology more broadly. More generally, latent variable models are deployed widely across many scientific disciplines. Thus, the argument we present in this work has much broader applications in AI for science if we want to move from impressive nonlinear neural network models to mathematically grounded methods that can help us learn something new about nature.

molecular biology↗

bioRxiv2024

NONEXPRESSOR OF PATHOGENESIS-RELATED GENES control Huanglongbing tolerance by regulating immune balance in citrus plants

Huanglongbing (HLB) is a devastating citrus disease caused by the phloem-resident bacterial pathogen Candidatus liberibacter asiaticus (CLas). CLas infection of susceptible varieties triggers unbalanced immune responses, leading to overaccumulation of callose and reactive oxygen species (ROS), which in turn causes phloem plugging and HLB symptom development. Interestingly, some citrus relatives exhibit little or no symptoms in the presence of CLas, a phenomenon termed HLB tolerance. Moreover, overexpression of the Arabidopsis thaliana NPR1 (AtNPR1) gene in susceptible varieties has been shown to confer robust HLB tolerance. However, the mechanisms underlying HLB tolerance remain enigmatic. Here, we show that overexpression of AtNPR1 suppresses CLas- and Pseudomonas syringae pv. maculicola ES4326 (Psm)-induced overaccumulation of callose and ROS in citrus and Arabidopsis, respectively. Importantly, we found that knocking out of the Arabidopsis negative immune regulators, AtNPR3 and AtNPR4, and silencing of their Citrus sinensis ortholog CsNPR3, similarly suppress Psm- and CLas-induced callose and ROS overaccumulation, respectively, and that silencing of CsNPR3 also enhances HLB tolerance. These results reveal a conserved role of the NPR1/NPR3/NPR4-mediated signaling pathway in regulating plant immune balances and provide mechanistic support for overexpression of AtNPR1 or silencing of AtNPR3/AtNPR4 orthologs in citrus as a long-term solution to the HLB disease.

plant biology↗

bioRxiv2023

Multiplexed gene editing with a multi-intron containing Cas9 gene in citrus

The citrus industry holds significant economic importance in Florida, being one of the leading producers of oranges and grapefruits in the United States. However, several diseases, such as canker and huanglongbing along with natural disasters like hurricanes have rigorously affected citrus production, quality, and yield. Improving citrus through traditional breeding methods requires significant challenges due to time constraints and complexity in genetic enhancements. To overcome these limitations, several expression systems have been developed in clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR/Cas9) framework allowing for gene editing of disease-associated genes across diverse citrus varieties. In this study, we present a new approach employing a multi-intron containing Cas9 gene plus multiple gRNAs separated with tRNA sequences to target the phytoene desaturase (PDS) gene in both Carrizo citrange and Duncan grapefruit. Notably, using this unified vector significantly boosted editing efficiency in both citrus varieties, showcasing mutations in all three designated targets. The implementation of this multiplex gene editing system with a multi-intron-containing Cas9 plus a gRNA-tRNA array demonstrates a promising avenue for efficient citrus genome editing, equipping us with potent tools in the ongoing battle against HLB. Statements and DeclarationsO_ST_ABSCompeting interestsC_ST_ABSThe authors declare that they have no competing interests. Supplementary InformationSupplementary File 1

plant biology↗

bioRxiv2023

Toxinome - The Bacterial Protein Toxin Database

Protein toxins are key molecular weapons in biology that are used to attack neighboring cells. Bacteria use protein toxins to kill or inhibit growth of prokaryotic and eukaryotic cells using various modes of action that target essential cellular components. The toxins are responsible for shaping microbiomes in different habitats, for abortive phage infection, and for severe infectious diseases of animals and plants. Although several toxin databases have been developed, each one is devoted to a specific toxin family and they encompass a relatively small number of toxins. Antimicrobial toxins are often accompanied by antitoxins (or immunity proteins) that neutralize the cognate toxins. Here, we combined toxins and antitoxins from many resources and created Toxinome, a comprehensive and updated bacterial protein toxin database. Toxinome includes a total of 1,483,028 toxins and 491,345 antitoxins encoded in 59,475 bacterial genomes across the tree of life. We identified a depletion of toxin and antitoxin genes in bacteria that dwell in extreme temperatures. We defined 5,161 unique Toxin Islands within phylogenetically diverse bacterial genomes, which are loci dense in toxin and antitoxin genes. By focusing on the unannotated genes within these islands, we characterized a number of these genes as toxins or antitoxins. Finally, we developed an interactive Toxinome website (http://toxinome.pythonanywhere.com) that allows searching and downloading of our database. The Toxinome resource will be useful to the large research community interested in bacterial toxins and can guide toxin discovery and function elucidation, and infectious disease diagnosis and treatment. ImportanceMicrobes use protein toxins as important tools to attack neighboring cells, microbial or eukaryotic, and for self-killing when attacked by viruses. These toxins work by different mechanisms to inhibit cell growth or kill cells. Microbes also use antitoxin proteins to neutralize the toxin activities. Here, we developed a comprehensive database called Toxinome of nearly two million toxin and antitoxins that are encoded in 59,475 bacterial genomes. We described the distribution of bacterial toxins and identified that they are depleted from bacteria that live in hot and cold temperatures. We find 5,161 cases in which toxins and antitoxins are densely clustered in bacterial genomes and termed these areas "Toxin Islands". The Toxinome database is a useful resource for anyone interested in toxin biology and evolution, and it can guide discovery of new toxins.

microbiology↗

bioRxiv2023

A genomic and structural bioinformatic pipeline identifies candidate type VI secretion antibacterial effector-immunity pairs

Type VI secretion systems (T6SS) are common bacterial contractile injection systems that inject toxic "effector" proteins into neighboring cells. We bioinformatically investigated T6SS core proteins in 11,832 genomes of Gram negative bacteria. Comparison of T6SS core proteins that are covalently attached to toxic T6SS effector proteins (T6Es) versus those that are not revealed differences in phylogenetic distribution, physical properties, and genomic position. Using the data generated from our bioinformatic analysis, we developed a new genomic- and Alphafold2-based pipeline for discovery of putative T6Es. We experimentally validated the toxic and immunity activities of four putative antibacterial T6SS effector proteins and four cognate immunity genes from diverse species, respectively. We used Foldseek to predict possible mechanisms of action of the putative T6Es, which was much more effective than sequence-based methods. Evidence of the possible mechanisms of action of the putative T6Es was explored through fluorescence microscopy, where we observed cell wall-targeting, DNA degradation, and cell filamentation. This study shows how combining genomic data mining with new structure-based bioinformatic tools can facilitate identification of novel antibacterial toxins.

microbiology↗

bioRxiv2022

Widespread horizontal gene transfer between plants and their microbiota

Plants host a large array of commensal bacteria that interact with the host. The growth of both bacteria and plants is often dependent on nutrients derived from the cognate partners, and the bacteria fine-tune host immunity against pathogens. This ancient interaction is common in all studied land plants and is critical for proper plant health and development. We hypothesized that the spatial vicinity and the long-term relationships between plants and their microbiota may promote or even depend on cross-kingdom horizontal gene transfer (HGT), a phenomenon that is relatively rare in nature. To test this hypothesis we analyzed the Arabidopsis thaliana genome and its extensively sequenced microbiome to detect events of horizontal transfer of full length genes that are absent from non-plant associated bacteria. Interestingly, we detected 180 unique genes that were horizontally transferred between plants and their microbiota. Genes transferred from plants to their microbiota are enriched in secreted proteins that metabolize carbohydrates, whereas microbes transferred to plants genes that are enriched in redox homeostasis functions. To validate our approach, we tested if a bacterial gene is functionally similar to its Arabidopsis homologue in planta. The Arabidopsis DET2 gene is essential for biosynthesis of the brassinosteroid phytohormones and loss-of-function of the gene leads to dwarfism. We found that expression of the DET2 homologue from Leifsonia bacteria of the Actinobacteria phylum in the Arabidopsis det2 background complements the mutant, and leads to normal plant growth. Together, these data suggest that cross-kingdom horizontal gene transfer events shape the interactions between plants and their microbiome. Significance statementWhat are the genes that shape host-microbe interactions and what are their origins are fundamental questions in molecular ecology and evolution. We explored the evolutionary mechanisms that formed Arabidopsis-microbiota interactions, as a model for host-microbe interactions. We found prevalent horizontal gene transfer, affecting 180 genes, that occurred between plants and their commensal microbiota. We propose that these genes participate in molecular mimicry between the host and its microbiome. Bacteria acquired from plants genes that primarily encode for secreted proteins that metabolize carbohydrates, thereby enabling bacteria to grow on plant-derived sugars. Additionally, we demonstrate how a bacterial gene that mimics a plant hormone biosynthesis gene can replace the plant gene function. Our results suggest that horizontal gene transfer between hosts and their microbiota is a significant and active evolutionary mechanism that contributed new traits to plants and their commensal microbiota.

evolutionary biology↗

bioRxiv2022

Accurate prediction of transition metal ion location via deep learning

Metal ions are essential cofactors for many proteins. In fact, currently, about half of the structurally characterized proteins contain a metal ion. Metal ions play a crucial role for many applications such as enzyme design or design of protein-protein interactions because they are biologically abundant, tether to the protein using strong interactions, and have favorable catalytic properties e.g. as Lewis acid. Computational design of metalloproteins is however hampered by the complex electronic structure of many biologically relevant metals such as zinc that can often not be accurately described using a classical force field. In this work, we develop two tools - Metal3D (based on 3D convolutional neural networks) and Metal1D (solely based on geometric criteria) to improve the identification and localization of zinc and other metal ions in experimental and computationally predicted protein structures. Comparison with other currently available tools shows that Metal3D is the most accurate metal ion location predictor to date outperforming geometric predictors including Metal1D by a wide margin using a single structure as input. Metal3D outputs a confidence metric for each predicted site and works on proteins with few homologes in the protein data bank. The predicted metal ion locations for Metal3D are within 0.70 {+/-} 0.64 [A] of the experimental locations with half of the sites below 0.5 [A]. Metal3D predicts a global metal density that can be used for annotation of structures predicted using e.g. AlphaFold2 and a per residue metal density that can be used in protein design workflows for the location of suitable metal binding sites and rotamer sampling to create novel metalloproteins. Metal3D is available as easy to use webapp, notebook or commandline interface.

biophysics↗

bioRxiv2022

Candidatus Liberibacter asiaticus reduces callose and reactive oxygen species production in the phloem

Huanglongbing (HLB) causes significant economic loss in citrus production worldwide. HLB is caused by Candidatus Liberibacter asiaticus (CLas), a gram-negative bacterium which inhabits the phloem exclusively. CLas infection results in accumulation of callose and reactive oxygen species in the phloem of infected plants, but little is known about the specific processes that take place during infection because of the sparse distribution of bacteria and the inaccessibility of the phloem inside the tree. In this study, we used the seed vasculatures, which accumulate a high number of CLas, as a model tissue to study CLas-host cellular interactions. In vasculature where CLas is abundant, sieve pore callose and H2O2 concentration were reduced compared to healthy seed vasculature. The expression of callose synthases (CalS) and respiratory burst oxidase homolog (RBOH) genes were downregulated in infected seeds compared to healthy ones. In leaves of HLB-infected plants, H2O2 concentration and CalS expression increased compared to uninfected leaves, but cells with CLas had lower levels of sieve plate callose compared to cells without CLas. Our results provide evidence that the bacteria manipulate cell metabolism to disable plant defenses and suggests that HLB disease is the result of a constant arms-race between the pathogen and a defense response, which is ultimately harmful to the host plant.

plant biology↗

bioRxiv2021

Systematic Discovery of Antimicrobial Polymorphic Toxins

Microbes employ toxins to kill competing microbes or eukaryotic host cells. Polymorphic toxins are proteins that encode C-terminal toxin domains. Here, we developed a computational approach to discover novel toxin domains of polymorphic toxins within 105,438 microbial genomes. We validated nine short novel toxins ("PTs") that cause bacterial or yeast cell death. The novel PTs are encoded by [~]2.2% of the sequenced bacteria, including numerous pathogens. We also identified five cognate immunity genes ("PIMs") that neutralize the toxins. Intriguingly, we observed an antifungal effect of the PTs against various pathogenic fungi. The toxins likely act as enzymes that cause severe damage to cell shape, membrane, and DNA. Finally, we solved the 3D structure of two PTs in complex with their PIMs, and showed that they function as novel DNAses. The new potent toxins likely play key roles in inter-microbial competition and can be utilized in various clinical and biotechnological applications.

microbiology↗

bioRxiv2021

Large-scale discovery of candidate type VI secretion effectors with antibacterial activity

Type VI secretion systems (T6SS) are common bacterial contractile injection systems that inject toxic "effector" proteins into neighboring cells. Effector discovery is generally done manually, and computational approaches used for effector discovery depend on genetic linkage to T6SS genes and/or sequence similarity to known effectors. We bioinformatically investigated T6SS in more than 11,832 genomes of Gram negative bacteria. We found that T6SS encoding bacteria are host-associated and pathogenic, enriched in specific human and plant tissues, while depleted in marine, soil, and engineered environments. Analysis of T6SS cores with C-terminal domains ("evolved" cores) showed "evolved" HCP are rare, overwhelmingly encoded in orphan operons, and are largely restricted to Escherichia. Using the wealth of data generated from our bioinformatic analysis, we developed two algorithms for large-scale discovery of T6SS effector proteins (T6Es). We experimentally validated ten putative antibacterial T6SS effector proteins and one cognate immunity gene from a diverse species. This study provides a systematic genomic perspective of the role of the T6SS in nature, a thorough analysis of T6E evolution and genomic properties, and discovery of a large number of candidate T6Es using new approaches.

microbiology↗

bioRxiv2021

Canopy health, but not Candidatus Liberibacter asiaticus Ct values, are correlated with fruit yield in Huanglongbing affected sweet orange trees.

In Florida, almost all citrus trees are infected with Huanglongbing (HLB), caused by the gram-negative, intracellular phloem limited bacteria Candidatus liberibacter asiaticus (CLas). Distinguishing between the severely and mildly sick trees is important for managing the groves and testing new HLB therapies. A mildly sick tree is one that produces higher fruit yield, compared to a severely sick tree, but measuring yields is laborious and time consuming. Here we characterized HLB affected sweet orange trees in the field in order to identify the specific traits that are correlated with the yields. We found that canopy volume, fruit detachment force (FDF) and the percentage of photosynthetically active radiation interception in the canopy (%INT) were positively correlated with fruit yields. Specifically, %INT measurements accurately distinguished between mild and severe trees in independent field trials. We could not find a difference in the Ct value between high and low producing HLB trees. Moreover, Ct values did not always agree with the number of CLas in the phloem that were visualized by transmission electron microscopy. Overall, our work identified an efficient way to distinguish between severe and mild HLB trees in Florida by measuring %INT and suggests that health of the canopy is more important for yields than the Ct value.

plant biology↗

bioRxiv2021

Transcriptome profiling of Candidatus Liberibacter asiaticus in citrus and psyllids

Candidatus Liberibacter asiaticus (Las) is an emergent bacterial pathogen that is associated with the devastating citrus Huanglongbing (HLB). Vectored by the Asian citrus psyllid, Las colonizes the phloem tissue of citrus, causing severe damage to infected trees. So far, cultivating pure Las culture in axenic media has not been successful and dual-transcriptome analyses aiming to profile gene expression in both Las and its host(s) have a low coverage of the Las genome due to the low abundance of bacterial RNA in total RNA extracts from infected tissues. Therefore, the lack of a Las transcriptome remains as a significant knowledge gap. Here, we used a bacterial cell enrichment procedure and confidently determined the expression profiles of approximately 84% of the Las genes. Genes that exhibited the highest expression levels in citrus include ion transporters, ferritin, outer membrane porins, and genes involved in phage-related functions, pilus formation, cell wall modification, and stress responses. One hundred and six genes were found to be differentially expressed in citrus vs psyllids. Genes related to transcription/translation and resilience to host defense response were upregulated in citrus; whereas genes involved in energy generation and the flagella system were expressed to higher levels in psyllids. We also determined the relative expression levels of potential Sec-dependent effectors, which are considered as key virulence factors of Las. This work advances our understanding of HLB biology and offers novel insight into the interactions of Las with its plant host and insect vector.

microbiology↗

bioRxiv2021

Phloem transport limitation in Huanglongbing affected sweet orange is dependent on phloem-limited bacteria and callose

Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (CLas), is a phloem-limited disease which disrupts citrus production in affected areas. In HLB-affected plants, phloem sieve plate pores accumulate callose, and leaf carbohydrate export is reduced. However, whether HLB causes a reduction in carbohydrate phloem translocation speed, and the quantitative relationships among callose, CLas population, and phloem translocation are still unknown. In this work, a procedure was developed to concurrently measure sugar transport, callose deposition, and relative pathogen population at different locations throughout the stem. Increasing quantities of CLas genetic material were positively correlated with quantity and density of callose deposits, and negatively correlated with phloem translocation speed. Callose deposit quantity was site- and rootstock dependent, and were negatively correlated with phloem translocation speed, suggesting a localized relationship. Remarkably, callose accumulation and phloem translocation disruption in the scion was dependent on rootstock genotype. Regression results suggested that the interaction of Ct values and number of phloem callose depositions, but not their size or density, explained the effects on translocation speed. Sucrose, starch, and sink 14C label allocation data support the interpretation of a transport pathway limitation by CLas infection. This work shows that the interaction of local accumulation of callose and CLas affect phloem transport. Further, the extent of this accumulation is attenuated by the rootstock and provides important information about the disease mechanism of phloem-inhabiting bacteria. Together, these results constitute the first example of a demonstrated transport limitation of phloem function by a microbial infection.

plant biology↗