Summary
Mushroom cropping consists of the development and fructification of different fungal species in soil or selective substrates that provide nutrients and support for the crop. The ...microorganisms present in these environments strongly influence, and in some cases are required for the growth and fructification of cultivated mushrooms. Some fungi such as truffles and morels form ectomycorrhizal associations with host plants. For these fungi, helper bacteria play an important role in the establishment of plant‐fungal symbioses. Selective processes acting on the microbiota present in substrates and soils determine the composition of the microbiota inhabiting the fruit bodies or interacting with fungal hyphae, and both configure the mushroom holobiont, understood as the fungus plus associated microorganisms. Here, we review current knowledge regarding the cross‐talk between bacteria and fungi during mushroom cultivation. We highlight the potential use of bioinoculants as agronomical amendments to increase mushroom productivity through growth promotion or as biocontrol agents to control pests and diseases.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Metals play essential roles in many biological processes but are toxic when present in excess. This makes their transport and homoeostatic control of particular importance to living ...organisms. Within the context of plant–pathogen interactions the availability and toxicity of transition metals can have a substantial impact on disease development. Metals are essential for defensive generation of reactive oxygen species and other plant defences and can be used directly to limit pathogen growth. Metal-based antimicrobials are used in agriculture to control plant disease, and there is increasing evidence that metal hyperaccumulating plants use accumulated metal to limit pathogen growth. Pathogens and hosts compete for available metals, with plants possessing mechanisms to withhold essential metals from invading microbes. Pathogens, meanwhile, use low-metal conditions as a signal to recognise and respond to the host environment. Consequently, metal-sensing systems such as
fur
(iron) and
zur
(zinc) regulate the expression of pathogenicity and virulence genes; and pathogens have developed sophisticated strategies to acquire metal during growth in plant tissues, including the production of multiple siderophores. This review explores the impact of transition metals on the processes that determine the outcome of bacterial infection in plants, with a particular emphasis on zinc, iron and copper.
This review discusses the pivotal role of transition metals such as zinc, copper and iron in determining the outcome of plant–pathogen interactions, both as essential mineral nutrients for plant and pathogen, and as anti-microbial agents that inhibit pathogen growth.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Efficient plant immune responses depend on the ability to recognise an invading microbe. The 22-amino acids in the N-terminal domain and the 28-amino acids in the central region of the bacterial ...flagellin, called flg22 and flgII-28, respectively, are important elicitors of plant immunity. Plant immunity is activated after flg22 or flgII-28 recognition by the plant transmembrane receptors FLS2 or FLS3, respectively. There is strong selective pressure on many plant pathogenic and endophytic bacteria to overcome flagellin-triggered immunity. Here we provide an overview of recent developments in our understanding of the evasion and suppression of flagellin pattern recognition by plant-associated bacteria.
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•Flagellin-triggered immunity relies on functional pattern recognition receptors (PRRs) and their interactors.•Bacteria subvert flagellin-triggered immunity before and after flagellin-derived PAMP recognition.•Bacteria manipulate flagellin synthesis, structure and degradation to impair PRR activation.•Bacteria secrete extracellular and intracellular effectors to suppress flagellin-triggered immune responses.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Plant pathogens such as fungi, oomycetes, viruses and bacteria infect important crops and account for significant economic losses worldwide. Therefore, it is critical to gain insights into ...plant-pathogen interactions at the cellular and molecular level. The outcome of the interaction between plants and pathogens greatly differs depending on the species, strains and cultivars involved as well as environmental factors, yet typically results in stress for the plant, the pathogen or both. These biotic-induced stresses can be monitored using a wide range of techniques, of which some of the most commonly used techniques are outlined in this chapter. One widely observed feature of biotic stress in plants is the generation of reactive oxygen species (ROS) such as hydrogen peroxide (H
O
) and superoxide (O
). We describe the quantification of hydrogen peroxide by 3,3'-diaminobenzidine (DAB) staining and luminol-based assays, and of superoxide by nitroblue tetrazolium (NBT) staining. Other techniques detailed here include measurement of callose deposition by aniline blue staining, evaluation of cell death by trypan blue staining and analysis of the loss of membrane integrity by monitoring electrolyte leakage.
Plants establish a pivotal relationship with their microbiome and are often conceptualized as holobionts. Nonetheless, holobiont theories have attracted much criticism, especially concerning the fact ...that the holobiont is rarely a unit of selection. In previous work, we discussed how the plant microbiome can be considered to be an 'ecosystem on a leash', which is subject to the influence of natural selection acting on plant traits. We proposed that in domesticated plants the assembly of the plant microbiome can usefully be conceptualized as being subject to a 'double leash', which encompasses both the effect of artificial selection imposed by the domesticator on plant traits and the leash from the plant to the microbiome. Here we approach the domesticated plant holobiont, simply defined as a community of organisms, from a community evolution point of view, and show how community heritability (a measure of community selection) complements the 'double-leash' framework in providing a community-level view of plant domestication and its impact on plant-microbe interactions. We also propose simple experiments that could be performed to investigate whether plant domestication has altered the potential for community selection at the holobiont level.
The evolution of cooperation in cellular groups is threatened by lineages of cheaters that proliferate at the expense of the group. These cell lineages occur within microbial communities, and ...multicellular organisms in the form of tumours and cancer. In contrast to an earlier study, here we show how the evolution of pleiotropic genetic architectures-which link the expression of cooperative and private traits-can protect against cheater lineages and allow cooperation to evolve. We develop an age-structured model of cellular groups and show that cooperation breaks down more slowly within groups that tie expression to a private trait than in groups that do not. We then show that this results in group selection for pleiotropy, which strongly promotes cooperation by limiting the emergence of cheater lineages. These results predict that pleiotropy will rapidly evolve, so long as groups persist long enough for cheater lineages to threaten cooperation. Our results hold when pleiotropic links can be undermined by mutations, when pleiotropy is itself costly, and in mixed-genotype groups such as those that occur in microbes. Finally, we consider features of multicellular organisms-a germ line and delayed reproductive maturity-and show that pleiotropy is again predicted to be important for maintaining cooperation. The study of cancer in multicellular organisms provides the best evidence for pleiotropic constraints, where abberant cell proliferation is linked to apoptosis, senescence, and terminal differentiation. Alongside development from a single cell, we propose that the evolution of pleiotropic constraints has been critical for cooperation in many cellular groups.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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•Forty one essential oils were evaluated against phytopathogenic bacteria.•Cinnamon and mustard essential oils inhibited bacterial growth at 0.016% (v/v).•Species-specific effect of ...oils: >67% showed specificity towards the pathogen.•Silica nanoparticle immobilisation increased cinnamaldehyde potency by 10-fold.•Cinnamaldehyde-nanoparticles eliminated up to 99.9% of bacterial growth.
Essential oils are volatile plant compounds that are biologically active and play an important role in natural plant protection. There are currently ∼3000 essential oils known, of which over 300 are commercially important for a variety of industries. In fact, the essential oil global market has been estimated to reach 13.94 billion USD with a demand of over 370,000 tons by 2024. These compounds have a wide variety of applications in agriculture, food and beverage, cosmetics, medicine, amongst other industries. A promising application of essential oils is as antimicrobials to target the vast number of diseases affecting crops. However, their volatile nature limits their effective use as free agents. To overcome this, we have investigated the use of mesoporous silica nanoparticles to protect essential oils from evaporation and degradation and to enhance their antimicrobial activity against bacterial phytopathogens. Silica nanoparticles were used due to their potential to be produced at an industrial scale and their biocompatibility. As a proof of concept, we evaluated 41 essential oils against bacterial phytopathogen Pseudomonas syringae pv. pisi, causative agent of pea bacterial blight. Additionally, we compared the effect of such essential oils against Pectobacterium carotovorum subsp. carotovorum and Pseudomonas fluorescens. Two of the most effective antimicrobials, cinnamon (Cinnamomum zeylanicum) and mustard (Brassica nigra) oils, were able to inhibit bacterial growth after 24 h at a concentration as low as 0.016% (v/v). Besides efficacy, the species-specificity of essential oils was demonstrated with >67% of oils tested displaying specificity towards pathogenic P. syringae pv. pisi over non-pathogenic Pseudomonas fluorescens. Furthermore, the encapsulation of essential oils into mesoporous silica nanoparticles (MSNPs) as a means of extending and improving their antimicrobial effect was found to enable a 10-fold increase in potency compared to the free essential oil. Cinnamaldehyde immobilised onto MSNPs proved to be the most effective antimicrobial, eliminating >99.8%, >99.9%, and >95% bacterial growth of P. fluorescens, P. syringae pv. pisi and P. carotovorum subsp. carotovorum, respectively. This system has the potential to be used to treat and prevent bacterial infections in crops and to enable a more controlled and effective exploitation of volatile compounds as antimicrobials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
One of the most fundamental questions in plant pathology is what determines whether a pathogen grows within a plant? This question is frequently studied in terms of the role of elicitors and ...pathogenicity factors in the triggering or overcoming of host defences. However, this focus fails to address the basic question of how the environment in host tissues acts to support or restrict pathogen growth. Efforts to understand this aspect of host-pathogen interactions are commonly confounded by several issues, including the complexity of the plant environment, the artificial nature of many experimental infection systems and the fact that the physiological properties of a pathogen growing in association with a plant can be very different from the properties of the pathogen in culture. It is also important to recognize that the phenotype and evolution of pathogen and host are inextricably linked through their interactions, such that the environment experienced by a pathogen within a host, and its phenotype within the host, is a product of both its interaction with its host and its evolutionary history, including its co-evolution with host plants. As the phenotypic properties of a pathogen within a host cannot be defined in isolation from the host, it may be appropriate to think of pathogens as having an 'extended phenotype' that is the product of their genotype, host interactions and population structure within the host environment. This article reflects on the challenge of defining and studying this extended phenotype, in relation to the questions posed below, and considers how knowledge of the phenotype of pathogens in the host environment could be used to improve disease control. What determines whether a pathogen grows within a plant? What aspects of pathogen biology should be considered in describing the extended phenotype of a pathogen within a host? How can we study the extended phenotype in ways that provide insights into the phenotypic properties of pathogens during natural infections?
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
The plant apoplast is the intercellular space that surrounds plant cells, in which metabolic and physiological processes relating to cell wall biosynthesis, nutrient transport, and stress responses ...occur. The apoplast is also the primary site of infection for hemibiotrophic pathogens such as P. syringae, which obtain nutrients directly from apoplastic fluid. We have used apoplastic fluid extracted from healthy tomato leaves as a growth medium for Pseudomonas spp. in order to investigate the role of apoplastic nutrients in plant colonization by Pseudomonas syringae. We have confirmed that apoplast extracts mimic some of the environmental and nutritional conditions that bacteria encounter during apoplast colonization by demonstrating that expression of the plant-induced type III protein secretion pathway is upregulated during bacterial growth in apoplast extracts. We used a modified phenoarray technique to show that apoplast-adapted P. syringae pv. tomato DC3000 expresses nutrient utilization pathways that allow it to use sugars, organic acids, and amino acids that are highly abundant in the tomato apoplast. Comparative analyses of the nutrient utilization profiles of the genome-sequenced strains P. syringae pv. tomato DC3000, P. syringae pv. syringae B728a, P. syringae pv. phaseolicola 1448A, and the unsequenced strain P. syringae pv. tabaci 11528 with nine other genome-sequenced strains of Pseudomonas provide further evidence that P. syringae strains are adapted to use nutrients that are abundant in the leaf apoplast. Interestingly, P. syringae pv. phaseolicola 1448A lacks many of the nutrient utilization abilities that are present in three other P. syringae strains tested, which can be directly linked to differences in the P. syringae pv. phaseolicola 1448A genome.
Abstract
Reactive oxygen species (ROS) are a key feature of plant (and animal) defences against invading pathogens. As a result, plant pathogens must be able to either prevent their production or ...tolerate high concentrations of these highly reactive chemicals. In this review, we focus on plant pathogenic bacteria of the genus Pseudomonas and the ways in which they overcome the challenges posed by ROS. We also explore the ways in which pseudomonads may exploit plant ROS generation for their own purposes and even produce ROS directly as part of their infection mechanisms.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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