The conference will be held in Poland's premier mountain resort of Zakopane, the beautiful and picturesque capital of the Polish High Tatra Mountains. Zakopane is a town in the south of Poland, approximately 110km south of Krakow and close to the border with Slovakia.
Phytoplasmas are insect-transmitted bacterial phytopathogens that secrete virulence effectors and induce changes in the architecture and defense response of their plant hosts. We previously demonstrated that the small (± 10 kDa) virulence effector SAP11 of Aster Yellows phytoplasma strain Witches' Broom (AY-WB) binds and destabilizes Arabidopsis CIN (CINCINNATA) TCP (TEOSINTE-BRANCHED, CYCLOIDEA, PROLIFERATION FACTOR 1 AND 2) transcription factors, resulting in dramatic changes in leaf morphogenesis and increased susceptibility to phytoplasma insect vectors. SAP11 contains a bipartite nuclear localization signal (NLS) that targets this effector to plant cell nuclei.To further understand how SAP11 functions, we assessed the involvement of SAP11 regions in TCP binding and destabilization using a series of mutants.SAP11 mutants lacking the entire N-terminal domain, including the NLS, interacted with TCPs but did not destabilize them. SAP11 mutants lacking the C-terminal domain were impaired in both binding and destabilization of TCPs. These SAP11 mutants did not alter leaf morphogenesis. A SAP11 mutant that did not accumulate in plant nuclei (SAP11ΔNLS-NES) was able to bind and destabilize TCP transcription factors, but instigated weaker changes in leaf morphogenesis than wild-type SAP11.Overall the results suggest that phytoplasma effector SAP11 has a modular organization in which at least three domains are required for efficient CIN-TCP destabilization in plants.
This book presents an overview of Phytophthora diseases. Taking into account the needs of graduate students, scientists, and agricultural professionals, this volume integrates guides to literature, background information, physiology and genetics, the effect of environmental factors on disease, control by biological and cultural means, resistant cultivars, fungicides, and techniques for recognizing, identifying, and isolating Phytophthora pathogens. Featured are detailed descriptions of 59 species, including photomicrographs and drawings, and discussion of related diseases, their development and control, and distribution. Generously illustrated and printed on high-quality enamel stock, this volume will be welcome by plant scientists and libraries worldwide.
Bacterial leaf streak of rice, caused by Xanthomonas oryzae pv. oryzicola (Xoc) is an increasingly important yield constraint in this staple crop. A mesophyll colonizer, Xoc differs from X. oryzae pv. oryzae (Xoo), which invades xylem to cause bacterial blight of rice. Both produce multiple distinct TAL effectors, type III-delivered proteins that transactivate effector-specific host genes. A TAL effector finds its target(s) via a partially degenerate code whereby the modular effector amino acid sequence identifies nucleotide sequences to which the protein binds. Virulence contributions of some Xoo TAL effectors have been shown, and their relevant targets, susceptibility (S) genes, identified, but the role of TAL effectors in leaf streak is uncharacterized. We used host transcript profiling to compare leaf streak to blight and to probe functions of Xoc TAL effectors. We found that Xoc and Xoo induce almost completely different host transcriptional changes. Roughly one in three genes upregulated by the pathogens is preceded by a candidate TAL effector binding element. Experimental analysis of the 44 such genes predicted to be Xoc TAL effector targets verified nearly half, and identified most others as false predictions. None of the Xoc targets is a known bacterial blight S gene. Mutational analysis revealed that Tal2g, which activates two genes, contributes to lesion expansion and bacterial exudation. Use of designer TAL effectors discriminated a sulfate transporter gene as the S gene. Across all targets, basal expression tended to be higher than genome-average, and induction moderate. Finally, machine learning applied to real vs. falsely predicted targets yielded a classifier that recalled 92% of the real targets with 88% precision, providing a tool for better target prediction in the future. Our study expands the number of known TAL effector targets, identifies a new class of S gene, and improves our ability to predict functional targeting.
Nuclear calcium oscillations are a hallmark of symbiotically stimulated plant root cells. Activation of the central nuclear decoder, calcium- and calmodulin-dependent kinase (CCaMK), triggers the entire symbiotic program including root nodule organogenesis, but the mechanism of signal transduction by CCaMK was unknown. We show that CYCLOPS, a direct phosphorylation substrate of CCaMK, is a DNA-binding transcriptional activator. Two phosphorylated serine residues within the N-terminal negative regulatory domain of CYCLOPS are necessary for its activity. CYCLOPS binds DNA in a sequence-specific and phosphorylation-dependent manner and transactivates the NODULE INCEPTION (NIN) gene. A phosphomimetic version of CYCLOPS was sufficient to trigger root nodule organogenesis in the absence of rhizobia and CCaMK. CYCLOPS thus induces a transcriptional activation cascade, in which NIN and a heterotrimeric NF-Y complex act in hierarchical succession to initiate symbiotic root nodule development
Bacterial pathogens of plant and animals share a homologous group of virulence factors, referred to as the YopJ effector family, which are translocated by the type III secretion (T3S) system into host cells during infection. Recent work indicates that some of these effectors encode acetyltransferases that suppress host immunity. The YopJ-like protein AvrBsT is known to activate effector-triggered immunity (ETI) in Arabidopsis thaliana Pi-0 plants; however, the nature of its enzymatic activity and host target(s) has remained elusive. Here we report that AvrBsT possesses acetyltransferase activity and acetylates ACIP1 (forACETYLATED INTERACTING PROTEIN1), an unknown protein from Arabidopsis. Genetic studies revealed that Arabidopsis ACIP family members are required for both pathogen-associated molecular pattern (PAMP)-triggered immunity and AvrBsT-triggered ETI duringPseudomonas syringae pathovar tomato DC3000 (Pst DC3000) infection. Microscopy studies revealed that ACIP1 is associated with punctae on the cell cortex and some of these punctae co-localize with microtubules. These structures were dramatically altered during infection. Pst DC3000 or Pst DC3000 AvrRpt2 infection triggered the formation of numerous, small ACIP1 punctae and rods. By contrast, Pst DC3000 AvrBsT infection primarily triggered the formation of large GFP-ACIP1 aggregates, in an acetyltransferase-dependent manner. Our data reveal that members of the ACIP family are new components of the defense machinery required for anti-bacterial immunity. They also suggest that AvrBsT-dependent acetylation in planta alters ACIP1's defense function, which is linked to the activation of ETI.
Pathogenicity of Pseudomonas syringae is dependent on a type III secretion system, which secretes a suite of virulence effector proteins into the host cytoplasm, and the production of a number of toxins such as coronatine (COR), which is a mimic of the plant hormone jasmonate-isoleuce (JA-Ile). Inside the plant cell, effectors target host molecules to subvert the host cell physiology and disrupt defenses. However, despite the fact that elucidating effector action is essential to understanding bacterial pathogenesis, the molecular function and host targets of the vast majority of effectors remain largely unknown. Here, we found that effector HopX1 fromPseudomonas syringae pv. tabaci (Pta) 11528, a strain that does not produce COR, interacts with and promotes the degradation of JAZ proteins, a key family of JA-repressors. We show that hopX1 encodes a cysteine protease, activity that is required for degradation of JAZs by HopX1. HopX1 associates with JAZ proteins through its central ZIM domain and degradation occurs in a COI1-independent manner. Moreover, ectopic expression of HopX1 in Arabidopsisinduces the expression of JA-dependent genes, represses salicylic acid (SA)-induced markers, and complements the growth of a COR-deficient P. syringae pv. tomato (Pto) DC3000 strain during natural bacterial infections. Furthermore, HopX1 promoted susceptibility when delivered by the natural type III secretion system, to a similar extent as the addition of COR, and this effect was dependent on its catalytic activity. Altogether, our results indicate that JAZ proteins are direct targets of bacterial effectors to promote activation of JA-induced defenses and susceptibility in Arabidopsis. HopX1 illustrates a paradigm of an alternative evolutionary solution to COR with similar physiological outcome.
Resistance in tomato against race 1 strains of the fungal vascular wilt pathogens Verticillium dahliae and V. albo-atrum is mediated by the Ve locus. This locus comprises two closely linked inversely oriented genes, Ve1 and Ve2, which encode cell surface receptors of the extracellular leucine-rich repeat receptor-like protein (eLRR-RLP) type. While Ve1 mediates Verticilliumresistance through monitoring the presence of the recently identified V. dahliae Ave1 effector, no functionality for Ve2 has been demonstrated in tomato. Ve1 and Ve2 contain 37 eLRRs and share 84% amino acid identity, facilitating investigation of Ve protein functionality through domain swapping. In this study it is shown that Ve chimeras in which the first thirty eLRRs of Ve1 were replaced by those of Ve2 remain able to induce HR and activate Verticilliumresistance, and that deletion of these thirty eLRRs from Ve1 resulted in loss of functionality. Also the region between eLRR30 and eLRR35 is required for Ve1-mediated resistance, and cannot be replaced by the region between eLRR30 and eLRR35 of Ve2. We furthermore show that the cytoplasmic tail of Ve1 is required for functionality, as truncation of this tail results in loss of functionality. Moreover, the C-terminus of Ve2 fails to activate immune signaling as chimeras containing the C-terminus of Ve2 do not provide Verticillium resistance. Furthermore, Ve1 was found to interact through its C-terminus with the eLRR-containing receptor-like kinase (eLRR-RLK) interactor SOBIR1 that was recently identified as an interactor of eLRR-RLP (immune) receptors. Intriguingly, also Ve2 was found to interact with SOBIR1.
Expression of chimeric receptors in plants is a way to activate specific signaling pathways by corresponding signal molecules. Defense signaling induced by chitin from pathogens and nodulation signaling of legumes induced by rhizobial Nod factor (NFs) depend on receptors with extracellular LysM domains. Here, we constructed chimeras by replacing the ectodomain of chitin elicitor receptor kinase 1 (AtCERK1) of Arabidopsis thaliana with ectodomains of NF receptors of Lotus japonicus (LjNFR1 and LjNFR5). The hybrid constructs, named LjNFR1-AtCERK1 and LjNFR5-AtCERK1, were expressed in cerk1-2, an A. thaliana CERK1 mutant lacking chitin-induced defense signaling. When treated with NFs from Rhizobium sp. NGR234, cerk1-2 expressing both chimeras accumulated reactive oxygen species, expressed chitin-responsive defense genes and showed increased resistance to Fusarium oxysporum. In contrast, expression of a single chimera showed no effects. Likewise, the ectodomains of LjNFR1 and LjNFR5 were replaced by those of OsCERK1 (Oryza sativa chitin elicitor receptor kinase 1) and OsCEBiP (O. sativa chitin elicitor binding protein), respectively. The chimeras, namedOsCERK1-LjNFR1 and OsCEBiP-LjNFR5, were expressed in L. japonicus NF receptor mutants (nfr1-1; nfr5-2) carrying a GUS (β-glucuronidase) gene under the control of the NIN (nodule inception) promoter. Upon chitin treatment, GUS activation reflecting nodulation signaling was observed in roots of NF receptor mutants expressing both chimeras, whereas a single construct was not sufficient for activation. Hence, replacement of ectodomains in LysM domain receptors provides a way to specifically trigger NF-induced defense signaling in non-legumes and chitin-induced nodulation signaling in legumes.
Plants sense potential pathogens by recognizing conserved pathogen-associated molecular patterns (PAMPs) that cause PAMP-triggered immunity (PTI). We previously reported that rice recognizes flagellin from the rice-incompatible N1141 strain of Acidovorax avenae and subsequently induces immune responses. Cell extracts isolated from flagellin-deficient N1141 (Δfla1141) still induced PTI responses, suggesting that Δfla1141 possesses an additional PAMP distinct from flagellin. Here, we show that elongation factor Tu (EF-Tu), one of the most abundant bacterial proteins, acts as a PAMP in rice and causes several PTI responses. In Brassicaceae species, EF-Tu and an N-acetylated peptide comprising the first 18 amino acids of the N-terminus, termed elf18, are fully active as inducers of PTI responses. By contrast, elf18 did not cause any immune responses in rice, whereas an EF-Tu middle region comprising Lys176 to Gly225, termed EFa50, is fully active as a PAMP in rice. In the leaves of rice plants, EF-Tu induced H2O2 generation and callose deposition, and also triggered resistance to coinfection with pathogenic bacteria. Taken together, these data demonstrate that rice recognizes EFa50, which is distinct from elf18, and that this epitope induces PTI responses.
Plants can be attacked by a vast range of pathogen classes, causing substantial agricultural losses. The Phytophthora (meaning “plant killer”) genus is a particularly destructive pathogen that causes root and stem base decay in a wide range of plants. Phytophthora infestans, which precipitated the Irish potato famine, originated in Central Mexico and is closely related to other Phytophthora species with distinct host ranges. Pathogen effectors that are secreted during infection play a key role in disease biology, but effector-induced adaptation to new hosts is an understudied topic. In this issue, Dong et al. investigate how Phytophthora effector proteins evolve the ability to specialize on new hosts (see the figure).
The biotrophic fungus Ustilago maydis causes smut disease in maize with characteristic tumor formation and anthocyanin induction. Here, we show that anthocyanin biosynthesis is induced by the virulence promoting secreted effector protein Tin2. Tin2 protein functions inside plant cells where it interacts with maize protein kinase ZmTTK1. Tin2 masks a ubiquitin–proteasome degradation motif in ZmTTK1, thus stabilizing the active kinase. Active ZmTTK1 controls activation of genes in the anthocyanin biosynthesis pathway. Without Tin2, enhanced lignin biosynthesis is observed in infected tissue and vascular bundles show strong lignification. This is presumably limiting access of fungal hyphae to nutrients needed for massive proliferation. Consistent with this assertion, we observe that maize brown midrib mutants affected in lignin biosynthesis are hypersensitive to U. maydis infection. We speculate that Tin2 rewires metabolites into the anthocyanin pathway to lower their availability for other defense responses. - See more at: http://elife.elifesciences.org/content/3/e01355#sthash.iLxIM1Ig.dpuf
The origins of many plant diseases appear to be recent and associated with the rise of domestication, the spread of agriculture or recent global movements of crops. Distinguishing between these possibilities is problematic because of the difficulty of determining rates of molecular evolution over short time frames. Heterochronous approaches using recent and historical samples show that plant viruses exhibit highly variable and often rapid rates of molecular evolution. The accuracy of estimated evolution rates and age of origin can be greatly improved with the inclusion of older molecular data from archaeological material. Here we present the first reconstruction of an archaeological RNA genome, which is of Barley Stripe Mosaic Virus (BSMV) isolated from barley grain ~750 years of age. Phylogenetic analysis of BSMV that includes this genome indicates the divergence of BSMV and its closest relative prior to this time, most likely around 2000 years ago. However, exclusion of the archaeological data results in an apparently much more recent origin of the virus that postdates even the archaeological sample. We conclude that this viral lineage originated in the Near East or North Africa, and spread to North America and East Asia with their hosts along historical trade routes.
The sessile plants have evolved a large number of receptor-like kinases (RLKs) and receptor-like cytoplasmic kinases (RLCKs) to modulate diverse biological processes, including plant innate immunity. Phosphorylation of the RLK/RLCK complex constitutes an essential step to initiate immune signaling. Two Arabidopsis plasma membrane-resident RLKs, flagellin-sensing 2 and brassinosteroid insensitive 1-associated kinase 1 (BAK1), interact with RLCK Botrytis-induced kinase 1 (BIK1) to initiate plant immune responses to bacterial flagellin. BAK1 directly phosphorylates BIK1 and positively regulates plant immunity. Classically defined as a serine/threonine kinase, BIK1 is shown here to possess tyrosine kinase activity with mass spectrometry, immunoblot, and genetic analyses. BIK1 is autophosphorylated at multiple tyrosine (Y) residues in addition to serine/threonine residues. Importantly, BAK1 is able to phosphorylate BIK1 at both tyrosine and serine/threonine residues. BIK1Y150 is likely catalytically important as the mutation blocks both tyrosine and serine/threonine kinase activity, whereas Y243 and Y250 are more specifically involved in tyrosine phosphorylation. The BIK1 tyrosine phosphorylation plays a crucial role in BIK1-mediated plant innate immunity as the transgenic plants carrying BIK1Y150F, Y243F, or Y250F (the mutation of tyrosine to phenylalanine) failed to complement the bik1 mutant deficiency in immunity. Our data indicate that plant RLCK BIK1 is a nonreceptor dual-specificity kinase and both tyrosine and serine/threonine kinase activities are required for its functions in plant immune signaling. Together with the previous finding of BAK1 to be autophosphorylated at tyrosine residues, our results unveiled the tyrosine phosphorylation cascade as a common regulatory mechanism that controls membrane-resident receptor signaling in plants and metazoans.
Agroinfiltration and PVX agroinfection are two efficient transient expression assays for functional analysis of candidate genes in plants. The most commonly used agent for agroinfiltration is Agrobacterium tumefaciens, a pathogen of many dicot plant species. This implies that agroinfiltration can be applied to many plant species. Here, we present our protocols and expected results when applying these methods to the potato (Solanum tuberosum), its related wild tuber-bearing Solanum species (Solanum section Petota) and the model plantNicotiana benthamiana. In addition to functional analysis of single genes, such as resistance (R) or avirulence (Avr) genes, the agroinfiltration assay is very suitable for recapitulating the R-AVR interactions associated with specific host pathogen interactions by simply delivering R and Avr transgenes into the same cell. However, some plant genotypes can raise nonspecific defense responses to Agrobacterium, as we observed for example for several potato genotypes. Compared to agroinfiltration, detection of AVR activity with PVX agroinfection is more sensitive, more high-throughput in functional screens and less sensitive to nonspecific defense responses to Agrobacterium. However, nonspecific defense to PVX can occur and there is a risk to miss responses due to virus-induced extreme resistance. Despite such limitations, in our experience, agroinfiltration and PVX agroinfection are both suitable and complementary assays that can be used simultaneously to confirm each other's results.
Fungal and oomycete plant parasites are among the most devastating pathogens of food crops. These microbes secrete effector proteins inside plant cells to manipulate host processes and facilitate colonization. How these effectors reach the host cytoplasm remains an unclear and debated area of plant research. In this article, we examine recent conflicting findings that have generated discussion in the field. We also highlight promising approaches based on studies of both parasite and host during infection. Ultimately, this knowledge may inform future broad spectrum strategies for protecting crops from such pathogens.
The α-proteobacterium Sinorhizobium meliloti establishes a chronic intracellular infection during the symbiosis with its legume hosts. Within specialized host cells, S. meliloti differentiates into highly polyploid, enlarged nitrogen-fixing bacteroids. This differentiation is driven by host cells through the production of defensin-like peptides called “nodule-specific cysteine-rich” (NCR) peptides. Recent research has shown that synthesized NCR peptides exhibit antimicrobial activity at high concentrations but cause bacterial endoreduplication at sublethal concentrations. We leveraged synchronized S. meliloti populations to determine how treatment with a sublethal NCR peptide affects the cell cycle and physiology of bacteria at the molecular level. We found that at sublethal levels a representative NCR peptide specifically blocks cell division and antagonizes Z-ring function. Gene-expression profiling revealed that the cell division block was produced, in part, through the substantial transcriptional response elicited by sublethal NCR treatment that affected ∼15% of the genome. Expression of critical cell-cycle regulators, including ctrA, and cell division genes, including genes required for Z-ring function, were greatly attenuated in NCR-treated cells. In addition, our experiments identified important symbiosis functions and stress responses that are induced by sublethal levels of NCR peptides and other antimicrobial peptides. Several of these stress-response pathways also are found in related α-proteobacterial pathogens and might be used by S. meliloti to sense host cues during infection. Our data suggest a model in which, in addition to provoking stress responses, NCR peptides target intracellular regulatory pathways to drive S. meliloti endoreduplication and differentiation during symbiosis.
Essentially all plant species exhibit heritable genetic variation for resistance to a variety of plant diseases caused by fungi, bacteria, oomycetes or viruses. Disease losses in crop monocultures are already significant, and would be greater but for applications of disease-controlling agrichemicals. For sustainable intensification of crop production, we argue that disease control should as far as possible be achieved using genetics rather than using costly recurrent chemical sprays. The latter imply CO2 emissions from diesel fuel and potential soil compaction from tractor journeys. Great progress has been made in the past 25 years in our understanding of the molecular basis of plant disease resistance mechanisms, and of how pathogens circumvent them. These insights can inform more sophisticated approaches to elevating disease resistance in crops that help us tip the evolutionary balance in favour of the crop and away from the pathogen. We illustrate this theme with an account of a genetically modified (GM) blight-resistant potato trial in Norwich, using the Rpi-vnt1.1 gene isolated from a wild relative of potato, Solanum venturii, and introduced by GM methods into the potato variety Desiree.
Powdery mildew is an important disease of cereals, affecting both grain yield and end-use quality. The causal agent of powdery mildew on cereals, Blumeria graminis, has been classified into eight formae speciales (ff.spp.), infecting crops and wild grasses. Advances in research on host specificity and resistance, and on pathogen phylogeny and origins, have brought aspects of the subspecific classification system ofB. graminis into ff.spp. into question, because it is based on adaptation to certain hosts rather than strict host specialization. Cereals therefore cannot be considered as typical non-hosts to non-adapted ff.spp. We introduce the term ‘non-adapted resistance’ of cereals to inappropriate ff.spp. of B. graminis, which involves both pathogen-associated molecular pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). There is no clear distinction between the mechanisms of resistance to adapted and non-adapted ff.spp. Molecular evolutionary data suggest that the taxonomic grouping of B. graminis into different ff.spp. is not consistent with the phylogeny of the fungus. Imprecise estimates of mutation rates and the lack of genetic variation in introduced populations may explain the uncertainty with regard to divergence times, in the Miocene or Holocene epochs, of ff.spp. of B. graminis which infect cereal crop species. We propose that most evidence favours divergence in the Holocene, during the course of early agriculture. We also propose that the forma specialis concept should be retained for B. graminis pathogenic on cultivated cereals to include clades of the fungus which are strongly specialized to these hosts, i.e. ff.spp. hordei, secalis and tritici, as well as avenae from cultivated A. sativa, and that the forma specialis concept should no longer be applied to B. graminis from most wild grasses.
------------------------------------------------------------------------ Characterization of a Tryptophan 2-Monooxygenase Gene from Puccinia graminis f. sp. tritici Involved in Auxin Biosynthesis and Rust Pathogenicity
------------------------------------------------------------------------ Mycosphaerella graminicola LysM Effector-Mediated Stealth Pathogenesis Subverts Recognition Through Both CERK1 and CEBiP Homologues in Wheat
------------------------------------------------------------------------ Production of Xylella fastidiosa Diffusible Signal Factor in Transgenic Grape Causes Pathogen Confusion and Reduction in Severity of Pierce's Disease
------------------------------------------------------------------------ Substitutions of Two Amino Acids in the Nucleotide-Binding Site Domain of a Resistance Protein Enhance the Hypersensitive Response and Enlarge the PM3F Resistance Spectrum in Wheat
------------------------------------------------------------------------ A Novel, Sensitive Method to Evaluate Potato Germplasm for Bacterial Wilt Resistance Using a Luminescent Ralstonia solanacearum Reporter Strain
The recognition between disease resistance (R) genes in plants and their cognate avirulence (Avr) genes in pathogens can produce a hypersensitive response of localized programmed cell death. However, our knowledge of the early signaling events of the R gene–mediated hypersensitive response in plants remains limited. Here, we report the cloning and characterization of Xa10, a transcription activator–like (TAL) effector-dependent R gene for resistance to bacterial blight in rice (Oryza sativa). Xa10 contains a binding element for the TAL effector AvrXa10 (EBEAvrXa10) in its promoter, and AvrXa10 specifically induces Xa10 expression. Expression of Xa10 induces programmed cell death in rice, Nicotiana benthamiana, and mammalian HeLa cells. The Xa10 gene product XA10 localizes as hexamers in the endoplasmic reticulum (ER) and is associated with ER Ca2+ depletion in plant and HeLa cells. XA10 variants that abolish programmed cell death and ER Ca2+ depletion in N. benthamiana and HeLa cells also abolish disease resistance in rice. We propose that XA10 is an inducible, intrinsic terminator protein that triggers programmed cell death by a conserved mechanism involving disruption of the ER and cellular Ca2+ homeostasis.
On August 8 and 9, 2014 (Friday and Saturday) a "North American Late Blight Symposium" will be held in Minneapolis, Minnesota, U.S.A., that will focus on the late blight diseases of potato and tomato. The symposium will last 1.5 days (all day Friday and Saturday until noon) and take place in the Minneapolis Convention Center. It will occur immediately before the joint meeting of the American and Canadian Phytopathological Societies, which is being held in the same location.
Details are still being finalized, but our meeting will include a keynote address by Geert Kessel of Wageningen University, shorter talks, and a poster session. The program will include the following topics:
• Epidemiology • Pathogen Biology and Diversity • Plant-based resistance • Integrated Disease Management • Chemical Control
Students and postdoctorals may apply for travel awards.
Thin sections of petrified fossils made during the latter part of the nineteenth and early twentieth centuries to investigate the internal tissue systems of plants now provide an important new source of information on associated micro-organisms. We report a new heterokont eukaryote (Combresomyces williamsoniisp. nov.) based on exquisitely preserved fossil oogonia, antheridia and hyphae from the Carboniferous (Pennsylvanian: Bashkirian stage) of UK. The structure of the oogonia and antheridia and features observed within the hyphae demonstrate a relationship with Oomycetes (Peronosporomycetes). The fossil micro-organism was documented in situ in petrified stem cortex and rootlets of the extinct seed fern Lyginopteris oldhamia (Pteridospermales). The main observed features point towards a pythiaceous Oomycete but links to biotrophic Albuginales or Peronosporaceae cannot be ruled out owing to the observation of a possible haustorium. Our study provides the earliest evidence for parasitism in Oomycetes.