- Plant Stress Physiology, Cross talk in plant stress signalling, Pseudomonas, Plant Pathology, Plant Physiology, Abiotic Stress, and 11 moreBiochemistry, Mineral Nutrition, Biological Sciences, Molecular Biology, Plant Molecular Biology, Plant Biology, Innate immunity, Mycosphaerella, Chalara fraxinae, Crop Diseases, and Food Securityedit
- I'm a plant pathologist currently working on: - Infection biology of Zymoseptoria tritici (Septoria Tritici Blotch of... moreI'm a plant pathologist currently working on:
- Infection biology of Zymoseptoria tritici (Septoria Tritici Blotch of wheat).
- & of Hymenoscyphus pseudoalbidus (ash dieback).
- Anti-fungals vs phytopathogens
- Climate change & food security: crop diseases
- Fusarium wilt of banana (Panama disease)
My main research interests are:
- Fungal and bacterial plant pathogens
- Plant defence signaling, stress signaling and crosstalk
- Climate change and food security
- Crop protection
- Metal hyperaccumulating plantsedit
Emerging pathogens of crops threaten food security and are increasingly problematic due to intensive agriculture and high volumes of trade and transport in plants and plant products. The ability to predict pathogen risk to agricultural... more
Emerging pathogens of crops threaten food security and are increasingly problematic due to intensive agriculture and high volumes of trade and transport in plants and plant products. The ability to predict pathogen risk to agricultural regions would therefore be valuable. However, predictions are complicated by multi-faceted relationships between crops, their pathogens, and climate change. Climate change is related to industrialization, which has brought not only a rise in greenhouse gas emissions but also an increase in other atmospheric pollutants. Here, we consider the implications of rising levels of reactive nitrogen gases and their manifold interactions with crops and crop diseases.
While fungi can make positive contributions to ecosystems and agro-ecosystems, for example, in mycorrhizal associations, they can also have devastating impacts as pathogens of plants and animals. In undisturbed ecosystems, most such... more
While fungi can make positive contributions to ecosystems and agro-ecosystems, for example, in mycorrhizal associations, they can also have devastating impacts as pathogens of plants and animals. In undisturbed ecosystems, most such negative interactions will be limited through the coevolution of fungi with their hosts. In this article, we explore what happens when pathogenic fungi spread beyond their natural ecological range and become invasive on naïve hosts in new ecosystems. We will see that such invasive pathogens have been problematic to humans and their domesticated plant and animal species throughout history, and we will discuss some of the most pressing fungal threats of today.
Zymoseptoria tritici is the causal agent of one of the European Union's most devastating foliar diseases of wheat: Septoria tritici Blotch (STB). It is also a notable pathogen of wheat grown in temperate climates throughout the world. In... more
Zymoseptoria tritici is the causal agent of one of the European Union's most devastating foliar diseases of wheat: Septoria tritici Blotch (STB). It is also a notable pathogen of wheat grown in temperate climates throughout the world. In this commentary, we highlight the importance of STB on wheat in the EU. To better understand STB, it is necessary to consider the host crop, the fungal pathogen and their shared environment. Here, we consider the fungus per se and its interaction with its host and then focus on a more agricultural overview of the impact STB on wheat. We consider the climatic and weather factors which influence its spread and severity, allude to the agricultural practices which may mitigate or enhance its impact on crop yields, and evaluate the economic importance of wheat as a food and animal feed crop in the UK and EU. Finally, we estimate the cost of STB disease to EU agriculture.
Research Interests:
The invasive pathogen, ash dieback fungus Hymenoscyphus fraxineus, is spreading rapidly across Europe. It shows high levels of outcrossing and limited population structure, even at the epidemic front. The anamorphic (asexual) form... more
The invasive pathogen, ash dieback fungus Hymenoscyphus fraxineus, is spreading rapidly across Europe. It shows high levels of outcrossing and limited population structure, even at the epidemic front. The anamorphic (asexual) form produces prolific conidia, thought to function solely as spermatia (male gametes), facilitating gene flow between sympatric strains. Here, we show that conidia are capable of germination on ash leaves and in vitro, and can infect seedlings via leaves or soil. In leaves, germlings form structures resembling fruiting bodies. Additionally, H. fraxineus colonises ash debris and grows in soil in the absence of ash tissues. We propose an amended life-cycle in which wind-dispersed, insect-vectored or water-spread conidia infect ash and may sporulate in planta, as well as in forest debris. This amplifies inoculum levels of different strains in ash stands. In combination with their function as spermatia, conidia thus act to maximise gene flow between sympatric strains, including those originally present at low inoculum. Such mixing increases evolutionary potential, as well as enhancing the likelihood of gene introgression from closely-related strains or assimilation of further genetic diversity from parental Asian populations. This scenario increases the adaptability of H. fraxineus to new climates and, indeed, onto new host species. The ascomycete fungus Hymenoscyphus fraxineus 1 is the causal agent of ash dieback 2. This disease is currently destroying ash trees across Europe 3–5. First observed in Poland in 1992 3 , it has now spread to more than 25 European countries 6. This pathogen is aggressive 7 , causing leaf necrosis, premature leaf drop, shoot wilting and crown dieback, as well as necrotic lesions on petioles, stems and root collars 7. Mortality is high in infected seedlings , whilst older trees develop chronic infections which are often eventually fatal (e.g. ref. 8). The loss of trees has a significant ecological and economic impact 9 , as ash is an important tree of mature woodland and hedgerows, as well as yielding commercial timber 10,11. Hymenoscyphus fraxineus is pleiomorphic; the anamorph (previously Chalara fraxinea 12) produces prolific asexual spores 13,14. However, these conidia have not been thought to have a role in the spread of the fungus, being described as " sticky " 3,15 and unlikely to become airborne. They are instead assumed to act as spermatia 13,16 during ascospore formation by the teleomorph (previously H. pseudoalbidus 17). This hypothesis is supported by the discovery that ascospores derived from individual apothecia show levels of genetic polymorphism indicative of multiple mating partners 13,14 and by the observation that the anamorph sporulates at the edge of the pseudoscle-rotial plate from which the apothecia emerge 18. Evidence suggests that sexual reproduction is of key importance the spread of H. fraxineus, a heterothallic fungus 13. Population genetic studies have found high intra-population variability, along with little inter-population variability 19 and a lack of population genetic structure 14,20–24 across the entire continent of Europe. These data indicate high gene flow between populations, consistent with a high rate of outcrossing 14. Indeed, while clear evidence of a founder effect can be seen when comparing the genotypes of the invasive pathogen populations in Europe with the much more variable genotypes displayed by native H. fraxineus populations in Asia, no such founder effect has been detected in the study of newly-discovered populations at the epidemic front 19. The closely-related species, Hymenoscyphus albidus, a non-pathogenic saprophyte on ash debris 25,26 , is being displaced
Research Interests:
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... more
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.
Research Interests:
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... more
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.
Research Interests:
Metal hyperaccumulating plants are able to accumulate exceptionally high concentrations of metals, such as zinc, nickel, or cadmium, in their aerial tissues. These metals reach concentrations that would be toxic to most other plant... more
Metal hyperaccumulating plants are able to accumulate exceptionally high concentrations of metals, such as zinc, nickel, or cadmium, in their aerial tissues. These metals reach concentrations that would be toxic to most other plant species. This trait has evolved multiple times independently in the plant kingdom. Recent studies have provided new insight into the ecological and evolutionary significance of this trait, by showing that some metal hyperaccumulating plants can use high concentrations of accumulated metals to defend themselves against attack by pathogenic microorganisms and herbivores. Here, we review the evidence that metal hyperaccumulation acts as a defensive trait in plants, with particular emphasis on plant-pathogen interactions. We discuss the mechanisms by which defense against pathogens might have driven the evolution of metal hyperaccumulation, including the interaction of this trait with other forms of defense. In particular, we consider how physiological adaptations and fitness costs associated with metal hyperaccumulation could have resulted in trade-offs between metal hyperaccumulation and other defenses. Drawing on current understanding of the population ecology of metal hyperaccumulator plants, we consider the conditions that might have been necessary for metal hyperaccumulation to be selected as a defensive trait, and discuss the likelihood that these were fulfilled. Based on these conditions, we propose a possible scenario for the evolution of metal hyperaccumulation, in which selective pressure for resistance to pathogens or herbivores, combined with gene flow from non-metallicolous populations, increases the likelihood that the metal hyperaccumulating trait becomes established in plant populations.
Metal-hyperaccumulating plants, which are hypothesized to use metals for defence against pests and pathogens, provide a unique context in which to study plant – pathogen coevolution. Previously, we demonstrated that the high... more
Metal-hyperaccumulating plants, which are hypothesized to use metals for defence against pests and pathogens, provide a unique context in which to study plant – pathogen coevolution. Previously, we demonstrated that the high concentrations of zinc found in leaves of the hyperaccumulator Noccaea caerulescens provide protection against bacterial pathogens, with a potential trade-off between metal-based and pathogen-induced defences. We speculated that an evolutionary arms race between zinc-based defences in N. caerulescens and zinc tolerance in pathogens might have driven the development of the hyperaccumulation phenotype. Here, we investigate the possibility of local adaptation by bacteria to the zinc-rich environment of N. caerulescens leaves and show that leaves sampled from the contaminated surroundings of a former mine site harboured endophytes with greater zinc tolerance than those within plants of an artificially created hyperaccumulat-ing population. Experimental manipulation of zinc concentrations in plants of this artificial population influenced the zinc tolerance of recovered endo-phytes. In laboratory experiments, only endophytic bacteria isolated from plants of the natural population were able to grow to high population densities in any N. caerulescens plants. These findings suggest that long-term coexistence with zinc-hyperaccumulating plants leads to local adaptation by endophytic bacteria to the environment within their leaves.
Research Interests:
Research Interests: Microbiology, Epidemiology, Immunology, Soil, Medical Microbiology, and 20 moreWestern blotting, Plant diseases, Mutagenesis, Molecular plant pathology, Disease resistance, Disease Resistance in plants, Polymerase Chain Reaction, Biocontrol, Zinc, Nickel, Cadmium, Pseudomonas Syringae, Metal Hyperaccumulators, Local adaptation, Thlaspi, Plant Disease Management, Oilseeds Pathology, Pulse Pest Protection, Drug Tolerance, and Plant Leaves
This chapter describes the steps needed to inoculate host plants with a fungus of interest, and subsequently to visualize the infection using confocal microscopy. As an exemplar, we consider the interaction between wheat and the Septoria... more
This chapter describes the steps needed to inoculate host plants with a fungus of interest, and subsequently to visualize the infection using confocal microscopy. As an exemplar, we consider the interaction between wheat and the Septoria leaf blotch fungus, Zymoseptoria tritici. This method is easiest when a GFP- or other fluorophore-tagged strain of the studied fungus is available, but notes are also provided which describe possible staining techniques which may be employed if fluorescent fungus is unavailable in your system.
The apoplast is a distinct extracellular compartment in plant tissues that lies outside the plasma membrane and includes the cell wall. The apoplastic compartment of plant leaves is the site of several important biological processes,... more
The apoplast is a distinct extracellular compartment in plant tissues that lies outside the plasma membrane and includes the cell wall. The
apoplastic compartment of plant leaves is the site of several important biological processes, including cell wall formation, cellular nutrient and
water uptake and export, plant-endophyte interactions and defence responses to pathogens. The infiltration-centrifugation method is well
established as a robust technique for the analysis of the soluble apoplast composition of various plant species. The fluid obtained by this method
is commonly known as apoplast washing fluid (AWF). The following protocol describes an optimized vacuum infiltration and centrifugation
method for AWF extraction from Phaseolus vulgaris (French bean) cv. Tendergreen leaves. The limitations of this method and the optimization
of the protocol for other plant species are discussed. Recovered AWF can be used in a wide range of downstream experiments that seek to
characterize the composition of the apoplast and how it varies in response to plant species and genotype, plant development and environmental
conditions, or to determine how microorganisms grow in apoplast fluid and respond to changes in its composition.
apoplastic compartment of plant leaves is the site of several important biological processes, including cell wall formation, cellular nutrient and
water uptake and export, plant-endophyte interactions and defence responses to pathogens. The infiltration-centrifugation method is well
established as a robust technique for the analysis of the soluble apoplast composition of various plant species. The fluid obtained by this method
is commonly known as apoplast washing fluid (AWF). The following protocol describes an optimized vacuum infiltration and centrifugation
method for AWF extraction from Phaseolus vulgaris (French bean) cv. Tendergreen leaves. The limitations of this method and the optimization
of the protocol for other plant species are discussed. Recovered AWF can be used in a wide range of downstream experiments that seek to
characterize the composition of the apoplast and how it varies in response to plant species and genotype, plant development and environmental
conditions, or to determine how microorganisms grow in apoplast fluid and respond to changes in its composition.
Research Interests:
Hitherto, pathogenicity assays with mutants or wildtype variants of Zymoseptoria tritici have been based on pycnidial counts, following inoculation of host leaves with high density inoculum. Here, we present data which suggest that high... more
Hitherto, pathogenicity assays with mutants or wildtype variants of Zymoseptoria tritici have been based on pycnidial counts, following inoculation of host leaves with high density inoculum. Here, we present data which suggest that high inoculum densities may mask deficiencies in virulence due to symptom saturation. We describe a low inoculum-density method which obviates this problem. This method can also be used to (i) interrogate the process of lesion formation in Z. tritici (ii) determine whether individuals of the same or different genotypes cooperate or compete during the establishment of apoplastic infections (iii) dissect the determinants of virulence, by assessing a given strain's stomatal penetration efficiency (SPE), its ability to spread within the apoplast and its pycnidiation efficiency. Such methodology can thus be used to investigate the reasons underpinning attenuated virulence in mutant or avirulent wildtype strains.
Research Interests:
Understanding the cellular organization and biology of fungal pathogens requires accurate methods for genomic integration of mutant alleles or fluorescent fusion-protein constructs. In Zymoseptoria tritici, this can be achieved by... more
Understanding the cellular organization and biology of fungal pathogens requires accurate methods for genomic integration of mutant alleles or fluorescent fusion-protein constructs. In Zymoseptoria tritici, this can be achieved by integrating of plasmid DNA randomly into the genome of this wheat pathogen. However, untargeted ectopic integration carries the risk of unwanted side effects, such as altered gene expression, due to targeting regulatory elements, or gene disruption following integration into protein-coding regions of the genome. Here, we establish the succinate dehydrogenase (sdi1) locus as a single ''soft-landing'' site for targeted ectopic integration of genetic constructs by using a carboxin-resistant sdi1 R allele, carrying the point-mutation H267L. We use various green and red fluorescent fusion constructs and show that 97% of all transformants integrate correctly into the sdi1 locus as single copies. We also demonstrate that such integration does not affect the pathogenicity of Z. tritici, and thus the sdi1 locus is a useful tool for virulence analysis in genetically modified Z. tritici strains. Furthermore, we have developed a vector which facilitates yeast recombination cloning and thus allows assembly of multiple overlapping DNA fragments in a single cloning step for high throughput vector and strain generation.