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826500.9923Mathematical modelling of CRISPR-Cas system effects on biofilm formation. Clustered regularly interspaced short palindromic repeats (CRISPR), linked with CRISPR associated (Cas) genes, can confer adaptive immunity to bacteria, against bacteriophage infections. Thus from a therapeutic standpoint, CRISPR immunity increases biofilm resistance to phage therapy. Recently, however, CRISPR-Cas genes have been implicated in reducing biofilm formation in lysogenized cells. Thus CRISPR immunity can have complex effects on phage-host-lysogen interactions, particularly in a biofilm. In this contribution, we develop and analyse a series of dynamical systems to elucidate and disentangle these interactions. Two competition models are used to study the effects of lysogens (first model) and CRISPR-immune bacteria (second model) in the biofilm. In the third model, the effect of delivering lysogens to a CRISPR-immune biofilm is investigated. Using standard analyses of equilibria, stability and bifurcations, our models predict that lysogens may be able to displace CRISPR-immune bacteria in a biofilm, and thus suggest strategies to eliminate phage-resistant biofilms.201728426329
813610.9923Recent progress in CRISPR/Cas9-based genome editing for enhancing plant disease resistance. Nowadays, agricultural production is strongly affected by both climate change and pathogen attacks which seriously threaten global food security. For a long time, researchers have been waiting for a tool allowing DNA/RNA manipulation to tailor genes and their expression. Some earlier genetic manipulation methods such as meganucleases (MNs), zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) allowed site directed modification but their successful rate was limited due to lack of flexibility when targeting a 'site-specific nucleic acid'. The discovery of clustered regularly interspaced short palindrome repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system has revolutionized genome editing domain in different living organisms during the past 9 years. Based on RNA-guided DNA/RNA recognition, CRISPR/Cas9 optimizations have offered an unrecorded scientific opportunity to engineer plants resistant to diverse pathogens. In this report, we describe the main characteristics of the primary reported-genome editing tools ((MNs, ZFNs, TALENs) and evaluate the different CRISPR/Cas9 methods and achievements in developing crop plants resistant to viruses, fungi and bacteria.202336871676
826420.9922Anti-CRISPR Phages Cooperate to Overcome CRISPR-Cas Immunity. Some phages encode anti-CRISPR (acr) genes, which antagonize bacterial CRISPR-Cas immune systems by binding components of its machinery, but it is less clear how deployment of these acr genes impacts phage replication and epidemiology. Here, we demonstrate that bacteria with CRISPR-Cas resistance are still partially immune to Acr-encoding phage. As a consequence, Acr-phages often need to cooperate in order to overcome CRISPR resistance, with a first phage blocking the host CRISPR-Cas immune system to allow a second Acr-phage to successfully replicate. This cooperation leads to epidemiological tipping points in which the initial density of Acr-phage tips the balance from phage extinction to a phage epidemic. Furthermore, both higher levels of CRISPR-Cas immunity and weaker Acr activities shift the tipping points toward higher initial phage densities. Collectively, these data help elucidate how interactions between phage-encoded immune suppressors and the CRISPR systems they target shape bacteria-phage population dynamics.201830033365
918230.9920Harnessing CRISPR/Cas9 in engineering biotic stress immunity in crops. There is significant potential for CRISPR/Cas9 to be used in developing crops that can adapt to biotic stresses such as fungal, bacterial, viral, and pest infections and weeds. The increasing global population and climate change present significant threats to food security by putting stress on plants, making them more vulnerable to diseases and productivity losses caused by pathogens, pests, and weeds. Traditional breeding methods are inadequate for the rapid development of new plant traits needed to counteract this decline in productivity. However, modern advances in genome-editing technologies, particularly CRISPR/Cas9, have transformed crop protection through precise and targeted modifications of plant genomes. This enables the creation of resilient crops with improved resistance to pathogens, pests, and weeds. This review examines various methods by which CRISPR/Cas9 can be utilized for crop protection. These methods include knocking out susceptibility genes, introducing resistance genes, and modulating defense genes. Potential applications of CRISPR/Cas9 in crop protection involve introducing genes that confer resistance to pathogens, disrupting insect genes responsible for survival and reproduction, and engineering crops that are resistant to herbicides. In conclusion, CRISPR/Cas9 holds great promise for advancing crop protection and ensuring food security in the face of environmental challenges and increasing population pressures. The most recent advancements in CRISPR technology for creating resistance to bacteria, fungi, viruses, and pests are covered here. We wrap up by outlining the most pressing issues and technological shortcomings, as well as unanswered questions for further study.202540663257
826840.9920Sustained coevolution of phage Lambda and Escherichia coli involves inner- as well as outer-membrane defences and counter-defences. Bacteria often evolve resistance to phage through the loss or modification of cell surface receptors. In Escherichia coli and phage λ, such resistance can catalyze a coevolutionary arms race focused on host and phage structures that interact at the outer membrane. Here, we analyse another facet of this arms race involving interactions at the inner membrane, whereby E. coli evolves mutations in mannose permease-encoding genes manY and manZ that impair λ's ability to eject its DNA into the cytoplasm. We show that these man mutants arose concurrently with the arms race at the outer membrane. We tested the hypothesis that λ evolved an additional counter-defence that allowed them to infect bacteria with deleted man genes. The deletions severely impaired the ancestral λ, but some evolved phage grew well on the deletion mutants, indicating that they regained infectivity by evolving the ability to infect hosts independently of the mannose permease. This coevolutionary arms race fulfils the model of an inverse gene-for-gene infection network. Taken together, the interactions at both the outer and inner membranes reveal that coevolutionary arms races can be richer and more complex than is often appreciated.202134032565
917450.9920Developing Phage Therapy That Overcomes the Evolution of Bacterial Resistance. The global rise of antibiotic resistance in bacterial pathogens and the waning efficacy of antibiotics urge consideration of alternative antimicrobial strategies. Phage therapy is a classic approach where bacteriophages (bacteria-specific viruses) are used against bacterial infections, with many recent successes in personalized medicine treatment of intractable infections. However, a perpetual challenge for developing generalized phage therapy is the expectation that viruses will exert selection for target bacteria to deploy defenses against virus attack, causing evolution of phage resistance during patient treatment. Here we review the two main complementary strategies for mitigating bacterial resistance in phage therapy: minimizing the ability for bacterial populations to evolve phage resistance and driving (steering) evolution of phage-resistant bacteria toward clinically favorable outcomes. We discuss future research directions that might further address the phage-resistance problem, to foster widespread development and deployment of therapeutic phage strategies that outsmart evolved bacterial resistance in clinical settings.202337268007
814560.9920Emerging role for RNA-based regulation in plant immunity. Infection by phytopathogenic bacteria triggers massive changes in plant gene expression, which are thought to be mostly a result of transcriptional reprogramming. However, evidence is accumulating that plants additionally use post-transcriptional regulation of immune-responsive mRNAs as a strategic weapon to shape the defense-related transcriptome. Cellular RNA-binding proteins regulate RNA stability, splicing or mRNA export of immune-response transcripts. In particular, mutants defective in alternative splicing of resistance genes exhibit compromised disease resistance. Furthermore, detection of bacterial pathogens induces the differential expression of small non-coding RNAs including microRNAs that impact the host defense transcriptome. Phytopathogenic bacteria in turn have evolved effector proteins to inhibit biogenesis and/or activity of cellular microRNAs. Whereas RNA silencing has long been known as an antiviral defense response, recent findings also reveal a major role of this process in antibacterial defense. Here we review the function of RNA-binding proteins and small RNA-directed post-transcriptional regulation in antibacterial defense. We mainly focus on studies that used the model system Arabidopsis thaliana and also discuss selected examples from other plants.201323163405
58970.9919Insulin Signaling and Insulin Resistance Facilitate Trained Immunity in Macrophages Through Metabolic and Epigenetic Changes. Adaptation of the innate immune system has been recently acknowledged, explaining sustained changes of innate immune responses. Such adaptation is termed trained immunity. Trained immunity is initiated by extracellular signals that trigger a cascade of events affecting cell metabolism and mediating chromatin changes on genes that control innate immune responses. Factors demonstrated to facilitate trained immunity are pathogenic signals (fungi, bacteria, viruses) as well non-pathogenic signals such as insulin, cytokines, adipokines or hormones. These signals initiate intracellular signaling cascades that include AKT kinases and mTOR as well as histone methylases and demethylases, resulting in metabolic changes and histone modifications. In the context of insulin resistance, AKT signaling is affected resulting in sustained activation of mTORC1 and enhanced glycolysis. In macrophages elevated glycolysis readily impacts responses to pathogens (bacteria, fungi) or danger signals (TLR-driven signals of tissue damage), partly explaining insulin resistance-related pathologies. Thus, macrophages lacking insulin signaling exhibit reduced responses to pathogens and altered metabolism, suggesting that insulin resistance is a state of trained immunity. Evidence from Insulin Receptor as well as IGF1Receptor deficient macrophages support the contribution of insulin signaling in macrophage responses. In addition, clinical evidence highlights altered macrophage responses to pathogens or metabolic products in patients with systemic insulin resistance, being in concert with cell culture and animal model studies. Herein, we review the current knowledge that supports the impact of insulin signaling and other insulin resistance related signals as modulators of trained immunity.201931244863
826980.9919Molecular genetics of Rhizobium Meliloti symbiotic nitrogen fixation. The application of recombinant DNA techniques to the study of symbiotic nitrogen fixation has yielded a growing list of Rhizobium meliloti genes involved in the processes of nodulation, infection thread formation and nitrogenase activity in nodules on the roots of the host plant, Medicago sativa (alfalfa). Interaction with the plant is initiated by genes encoding sensing and motility systems by which the bacteria recognizes and approaches the root. Signal molecules, such as flavonoids, mediate a complex interplay of bacterial and plant nodulation genes leading to entry of the bacteria through a root hair. As the nodule develops, the bacteria proceed inward towards the cortex within infection threads, the formation of which depends on bacterial genes involved in polysaccharide synthesis. Within the cortex, the bacteria enter host cells and differentiate into forms known as bacteroids. Genes which encode and regulate nitrogenase enzyme are expressed in the mature nodule, together with other genes required for import and metabolism of carbon and energy sources offered by the plant.198914542173
826790.9919Why put up with immunity when there is resistance: an excursion into the population and evolutionary dynamics of restriction-modification and CRISPR-Cas. Bacteria can readily generate mutations that prevent bacteriophage (phage) adsorption and thus make bacteria resistant to infections with these viruses. Nevertheless, the majority of bacteria carry complex innate and/or adaptive immune systems: restriction-modification (RM) and CRISPR-Cas, respectively. Both RM and CRISPR-Cas are commonly assumed to have evolved and be maintained to protect bacteria from succumbing to infections with lytic phage. Using mathematical models and computer simulations, we explore the conditions under which selection mediated by lytic phage will favour such complex innate and adaptive immune systems, as opposed to simple envelope resistance. The results of our analysis suggest that when populations of bacteria are confronted with lytic phage: (i) In the absence of immunity, resistance to even multiple bacteriophage species with independent receptors can evolve readily. (ii) RM immunity can benefit bacteria by preventing phage from invading established bacterial populations and particularly so when there are multiple bacteriophage species adsorbing to different receptors. (iii) Whether CRISPR-Cas immunity will prevail over envelope resistance depends critically on the number of steps in the coevolutionary arms race between the bacteria-acquiring spacers and the phage-generating CRISPR-escape mutants. We discuss the implications of these results in the context of the evolution and maintenance of RM and CRISPR-Cas and highlight fundamental questions that remain unanswered. This article is part of a discussion meeting issue 'The ecology and evolution of prokaryotic CRISPR-Cas adaptive immune systems'.201930905282
8139100.9919TAL effectors: highly adaptable phytobacterial virulence factors and readily engineered DNA-targeting proteins. Transcription activator-like (TAL) effectors are transcription factors injected into plant cells by pathogenic bacteria of the genus Xanthomonas. They function as virulence factors by activating host genes important for disease, or as avirulence factors by turning on genes that provide resistance. DNA-binding specificity is encoded by polymorphic repeats in each protein that correspond one-to-one with different nucleotides. This code has facilitated target identification and opened new avenues for engineering disease resistance. It has also enabled TAL effector customization for targeted gene control, genome editing, and other applications. This article reviews the structural basis for TAL effector-DNA specificity, the impact of the TAL effector-DNA code on plant pathology and engineered resistance, and recent accomplishments and future challenges in TAL effector-based DNA targeting.201323707478
8253110.9919Strategies used by bacterial pathogens to suppress plant defenses. Plant immune systems effectively prevent infections caused by the majority of microbial pathogens that are encountered by plants. However, successful pathogens have evolved specialized strategies to suppress plant defense responses and induce disease susceptibility in otherwise resistant hosts. Recent advances reveal that phytopathogenic bacteria use type III effector proteins, toxins, and other factors to inhibit host defenses. Host processes that are targeted by bacteria include programmed cell death, cell wall-based defense, hormone signaling, the expression of defense genes, and other basal defenses. The discovery of plant defenses that are vulnerable to pathogen attack has provided new insights into mechanisms that are essential for both bacterial pathogenesis and plant disease resistance.200415231256
8335120.9918Implementing Optogenetic-Controlled Bacterial Systems in Drosophila melanogaster for Alleviation of Heavy Metal Poisoning. Drosophila melanogaster (fruit fly) is an animal model chassis in biological and genetic research owing to its short life cycle, ease of cultivation, and acceptability to genetic modification. While the D. melanogaster chassis offers valuable insights into drug efficacy, toxicity, and mechanisms, several obvious challenges such as dosage control and drug resistance still limit its utility in pharmacological studies. Our research combines optogenetic control with engineered gut bacteria to facilitate the precise delivery of therapeutic substances in D. melanogaster for biomedical research. We have shown that the engineered bacteria can be orally administered to D. melanogaster to get a stable density of approximately 28,000 CFUs/per fly, leading to no detectable negative effects on the growth of D. melanogaster. In a model of D. melanogaster exposure to heavy metal, these orally administered bacteria uniformly express target genes under green light control to produce MtnB protein for binding and detoxifying lead, which significantly reduces the level of oxidative stress in the intestinal tract of Pb-treated flies. This pioneering study lays the groundwork for using optogenetic-controlled bacteria in the model chassis D. melanogaster to advance biomedical applications.202439312764
8134130.9918Sweet scents from good bacteria: Case studies on bacterial volatile compounds for plant growth and immunity. Beneficial bacteria produce diverse chemical compounds that affect the behavior of other organisms including plants. Bacterial volatile compounds (BVCs) contribute to triggering plant immunity and promoting plant growth. Previous studies investigated changes in plant physiology caused by in vitro application of the identified volatile compounds or the BVC-emitting bacteria. This review collates new information on BVC-mediated plant-bacteria airborne interactions, addresses unresolved questions about the biological relevance of BVCs, and summarizes data on recently identified BVCs that improve plant growth or protection. Recent explorations of bacterial metabolic engineering to alter BVC production using heterologous or endogenous genes are introduced. Molecular genetic approaches can expand the BVC repertoire of beneficial bacteria to target additional beneficial effects, or simply boost the production level of naturally occurring BVCs. The effects of direct BVC application in soil are reviewed and evaluated for potential large-scale field and agricultural applications. Our review of recent BVC data indicates that BVCs have great potential to serve as effective biostimulants and bioprotectants even under open-field conditions.201626177913
8256140.9918Revolutionizing Tomato Cultivation: CRISPR/Cas9 Mediated Biotic Stress Resistance. Tomato (Solanum lycopersicon L.) is one of the most widely consumed and produced vegetable crops worldwide. It offers numerous health benefits due to its rich content of many therapeutic elements such as vitamins, carotenoids, and phenolic compounds. Biotic stressors such as bacteria, viruses, fungi, nematodes, and insects cause severe yield losses as well as decreasing fruit quality. Conventional breeding strategies have succeeded in developing resistant genotypes, but these approaches require significant time and effort. The advent of state-of-the-art genome editing technologies, particularly CRISPR/Cas9, provides a rapid and straightforward method for developing high-quality biotic stress-resistant tomato lines. The advantage of genome editing over other approaches is the ability to make precise, minute adjustments without leaving foreign DNA inside the transformed plant. The tomato genome has been precisely modified via CRISPR/Cas9 to induce resistance genes or knock out susceptibility genes, resulting in lines resistant to common bacterial, fungal, and viral diseases. This review provides the recent advances and application of CRISPR/Cas9 in developing tomato lines with resistance to biotic stress.202439204705
8135150.9917Harnessing Genome Editing Techniques to Engineer Disease Resistance in Plants. Modern genome editing (GE) techniques, which include clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9) system, transcription activator-like effector nucleases (TALENs), zinc-finger nucleases (ZFNs) and LAGLIDADG homing endonucleases (meganucleases), have so far been used for engineering disease resistance in crops. The use of GE technologies has grown very rapidly in recent years with numerous examples of targeted mutagenesis in crop plants, including gene knockouts, knockdowns, modifications, and the repression and activation of target genes. CRISPR/Cas9 supersedes all other GE techniques including TALENs and ZFNs for editing genes owing to its unprecedented efficiency, relative simplicity and low risk of off-target effects. Broad-spectrum disease resistance has been engineered in crops by GE of either specific host-susceptibility genes (S gene approach), or cleaving DNA of phytopathogens (bacteria, virus or fungi) to inhibit their proliferation. This review focuses on different GE techniques that can potentially be used to boost molecular immunity and resistance against different phytopathogens in crops, ultimately leading to the development of promising disease-resistant crop varieties.201931134108
9192160.9917Antimicrobial peptides: Sustainable application informed by evolutionary constraints. The proliferation and global expansion of multidrug-resistant (MDR) bacteria have deepened the need to develop novel antimicrobials. Antimicrobial peptides (AMPs) are regarded as promising antibacterial agents because of their broad-spectrum antibacterial activity and multifaceted mechanisms of action with non-specific targets. However, if AMPs are to be applied sustainably, knowledge of how they induce resistance in pathogenic bacteria must be mastered to avoid repeating the traditional antibiotic resistance mistakes currently faced. Furthermore, the evolutionary constraints on the acquisition of AMP resistance by microorganisms in the natural environment, such as functional compatibility and fitness trade-offs, inform the translational application of AMPs. Consequently, the shortcut to achieve sustainable utilization of AMPs is to uncover the evolutionary constraints of bacteria on AMP resistance in nature and find the tricks to exploit these constraints, such as applying AMP cocktails to minimize the efficacy of selection for resistance or combining nanomaterials to maximize the costs of AMP resistance. Altogether, this review dissects the benefits, challenges, and opportunities of utilizing AMPs against disease-causing bacteria, and highlights the use of AMP cocktails or nanomaterials to proactively address potential AMP resistance crises in the future.202235752270
9176170.9917Evolutionary Dynamics between Phages and Bacteria as a Possible Approach for Designing Effective Phage Therapies against Antibiotic-Resistant Bacteria. With the increasing global threat of antibiotic resistance, there is an urgent need to develop new effective therapies to tackle antibiotic-resistant bacterial infections. Bacteriophage therapy is considered as a possible alternative over antibiotics to treat antibiotic-resistant bacteria. However, bacteria can evolve resistance towards bacteriophages through antiphage defense mechanisms, which is a major limitation of phage therapy. The antiphage mechanisms target the phage life cycle, including adsorption, the injection of DNA, synthesis, the assembly of phage particles, and the release of progeny virions. The non-specific bacterial defense mechanisms include adsorption inhibition, superinfection exclusion, restriction-modification, and abortive infection systems. The antiphage defense mechanism includes a clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated (Cas) system. At the same time, phages can execute a counterstrategy against antiphage defense mechanisms. However, the antibiotic susceptibility and antibiotic resistance in bacteriophage-resistant bacteria still remain unclear in terms of evolutionary trade-offs and trade-ups between phages and bacteria. Since phage resistance has been a major barrier in phage therapy, the trade-offs can be a possible approach to design effective bacteriophage-mediated intervention strategies. Specifically, the trade-offs between phage resistance and antibiotic resistance can be used as therapeutic models for promoting antibiotic susceptibility and reducing virulence traits, known as bacteriophage steering or evolutionary medicine. Therefore, this review highlights the synergistic application of bacteriophages and antibiotics in association with the pleiotropic trade-offs of bacteriophage resistance.202235884169
9180180.9916Novel genes for disease-resistance breeding. Plant disease control is entering an exciting period during which transgenic plants showing improved resistance to pathogenic viruses, bacteria, fungi and insects are being developed. This review summarizes the first successful attempts to engineer fungal resistance in crops, and highlights two promising approaches. Biotechnology provides the promise of new integrated disease management strategies that combine modern fungicides and transgenic crops to provide effective disease control for modern agriculture.200010712959
8153190.9916Dominant, Heritable Resistance to Stewart's Wilt in Maize Is Associated with an Enhanced Vascular Defense Response to Infection with Pantoea stewartii. Vascular wilt bacteria such as Pantoea stewartii, the causal agent of Stewart's bacterial wilt of maize (SW), are destructive pathogens that are difficult to control. These bacteria colonize the xylem, where they form biofilms that block sap flow leading to characteristic wilting symptoms. Heritable forms of SW resistance exist and are used in maize breeding programs but the underlying genes and mechanisms are mostly unknown. Here, we show that seedlings of maize inbred lines with pan1 mutations are highly resistant to SW. However, current evidence suggests that other genes introgressed along with pan1 are responsible for resistance. Genomic analyses of pan1 lines were used to identify candidate resistance genes. In-depth comparison of P. stewartii interaction with susceptible and resistant maize lines revealed an enhanced vascular defense response in pan1 lines characterized by accumulation of electron-dense materials in xylem conduits visible by electron microscopy. We propose that this vascular defense response restricts P. stewartii spread through the vasculature, reducing both systemic bacterial colonization of the xylem network and consequent wilting. Though apparently unrelated to the resistance phenotype of pan1 lines, we also demonstrate that the effector WtsE is essential for P. stewartii xylem dissemination, show evidence for a nutritional immunity response to P. stewartii that alters xylem sap composition, and present the first analysis of maize transcriptional responses to P. stewartii infection.201931657672