Host jumping is a process by which pathogens settle in new host groups. It is a cornerstone in the evolution of pathogens, as it leads to pathogen diversification. It is unsurprising that host ...jumping is observed in facultative pathogens, as they can reproduce even if they kill their hosts. However, host jumps were thought to be rare in obligate biotrophic pathogens, but molecular phylogenetics has revealed that the opposite is true. Here, I review some concepts and recent findings and present several hypotheses on the matter. In short, pathogens evolve and diversify via host jumps, followed by radiation, specialisation and speciation. Host jumps are facilitated by, for example, effector innovations, stress, compatible pathogens and physiological similarities. Host jumping, subsequent establishment, and speciation takes place rapidly – within centuries and millennia rather than over millions of years. If pathogens are unable to evolve into neutral or mutualistic interactions with their hosts, they will eventually be removed from the host population, despite balancing trade-offs. Thus, generally, plant pathogens only survive in the course of evolution if they jump hosts. This is also reflected by the diversity patterns observed in many genera of plant pathogens, where it leads to a mosaic pattern of host groups over time, in which the original host group becomes increasingly obscure.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Oomycetes are a diverse group of eukaryotic organisms that have colonised many ecological niches; yet more than 60% of the known species are parasitic on plants. Parasitism of plants has evolved ...several times independently in three different lineages of the Oomycota. Here, we provide an overview of the current knowledge of the diversity, evolution and lifestyles of plant parasitic oomycetes. We then report on recent advances in molecular studies on oomycete–plant interactions with a particular emphasis on work with oomycete effectors. In the future, genome sequencing of a broader spectrum of oomycete species will expand our knowledge of pathogenicity mechanisms and will likely reveal novel structural and functional classes of effectors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Downy mildew species in the genus
Plasmopara
are obligate biotrophic pathogens responsible for destructive diseases of economically important cultivated and ornamental plants. During September 2020 ...and 2021, a downy mildew was observed on porcelain berry (
Ampelopsis grandulosa
var.
brevipedunculata
) in different locations in MD, USA. A total of thirteen samples were collected from an equal number of diseased plants. Phylogenetic analyses of the cytochrome c oxidase subunit 2 (
cox2
) and large subunit ribosomal RNA (nc LSU rDNA) gene regions indicated that they constituted an unknown species here described as
Plasmopara ampelopsidis
sp. nov. Concurrently, a second species on wild
Vitis
species was also found, among historical downy mildew specimens used in previous studies, and it is here described as
Plasmopara carveri
. These newly described species are closely related to
Plasmopara viticola
and
Plasmopara muralis
. Although molecular phylogenetic analyses strongly support the segregation of these species, diagnostic morphological characters for each species were not observed. Therefore, a list of specific substitutions in the
cox2
region as diagnostic characters is provided. It remains unclear if these new species represent a threat to the grapevine industry, but it seems advisable to closely monitor the presence of the two species.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Even though the microevolution of plant hosts and pathogens has been intensely studied, knowledge regarding macro-evolutionary patterns is limited. Having the highest species diversity and ...host-specificity among Oomycetes, downy mildews are a useful a model for investigating long-term host-pathogen coevolution. We show that phylogenies of Bremia and Asteraceae are significantly congruent. The accepted hypothesis is that pathogens have diverged contemporarily with their hosts. But maximum clade age estimation and sequence divergence comparison reveal that congruence is not due to long-term coevolution but rather due to host-shift driven speciation (pseudo-cospeciation). This pattern results from parasite radiation in related hosts, long after radiation and speciation of the hosts. As large host shifts free pathogens from hosts with effector triggered immunity subsequent radiation and diversification in related hosts with similar innate immunity may follow, resulting in a pattern mimicking true co-divergence, which is probably limited to the terminal nodes in many pathogen groups.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Downy mildew disease of sunflower, caused by the obligate biotrophic oomycete Plasmopara halstedii, can have significant economic impact on sunflower cultivation. Using high-throughput whole ...transcriptome sequencing, four developmental phases in 16 time-points of Pl. halstedii infecting Helianthus annuus were investigated. With the aim of identifying potential functional and regulatory motifs upstream of co-expressed genes, time-series derived gene expression profiles were clustered based on their time-course similarity, and their upstream regulatory gene sequences were analyzed here. Several conserved motifs were found upstream of co-expressed genes, which might be involved in binding specific transcription factors. Such motifs were also found associated with virulence related genes, and could be studied on a genetically tractable model to clarify, if these are involved in regulating different stages of pathogenesis.
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Downy mildews and root and foliar rots caused by Phytophthora are among the most destructive plant pathogens and therefore have attracted considerable attention during the past two decades. Although ...it has been realized that a close phylogenetic relationship exists, so far sharp distinction has been made between the obligate biotrophic downy mildews and the hemibiotrophic Phytophthora. In the study presented here, it is shown that a continuum of character states from hemibiotrophic Phytophthora species to obligate biotrophic downy mildews is present. Intermediate character states between downy mildews and Phytophthora species exist in several rare parasites of grasses, which are not embedded within the major clades of the downy mildews but are placed sister to these, with unresolved affinities to both these clades and to Phytophthora. They still have retained traits hitherto thought to be exclusive for Phytophthora. A careful review of previous research is presented and it is highlighted that uniquely for downy mildews, Poakatesthia may form an intracellular mycelium, growing through several host cells. In addition, scanning electron microscopy reveals that sporangiophore growth is not determinate in Viennotia and that outgrowth from sporangiophores is very similar to Phytophthora infestans. It is concluded that the sharp morphological distinction between downy mildews and Phytophthora species (that are often placed in separate families and even different orders), is rather artificial, since all features thought to be exclusive to Phytophthora or the downy mildews are united in the rare grass-parasitizing down mildew genera Viennotia and Poakatesthia and the enigmatic genus Sclerophthora. Therefore, several paradigms regarding the distinction between Phytophthora and the downy mildews need to be reconsidered.
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Oomycetes, a large group of fungus-like organisms, include some destructive plant pathogens causing enormous economic damage. Phylogenetically, oomycetes belong to the kingdom
Straminipila
and ...have diverse lifestyles, including saprotrophs and both general and specialized pathogens of various eukaryotic supergroups. A rapid increase in genomic studies and next-generation sequencing technologies have led to significant progress in understanding oomycete lifestyles. However, their genetics, including transcriptional regulation, have been studied to a much lesser extent. Here, we provide a cross-species analysis of oomycete promoter for providing a first step towards elucidating gene regulation networks related to pathogenicity and life cycle stages. The clustered DNA sequences of
Plasmopara halstedii
transcriptome time-series expression level dataset from a preliminary study have been used as a core reference for cross-species comparisons. Using a computational pipeline, 46 potential transcription factor binding site (TFBS) motifs in 25 clusters with functionally conserved downstream genes of downy mildew and two
Phytophthora
species, regardless of the gene expression levels of
Phytophthora
transcriptomes, were found. This can now be followed up by knock-out experiments in oomycete species amenable for genetic modification.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Phytophthora infestans, the cause of potato late blight, is infamous for having triggered the Irish Great Famine in the 1840s. Until the late 1970s, P. infestans diversity outside of its Mexican ...center of origin was low, and one scenario held that a single strain, US-1, had dominated the global population for 150 years; this was later challenged based on DNA analysis of historical herbarium specimens. We have compared the genomes of 11 herbarium and 15 modern strains. We conclude that the 19th century epidemic was caused by a unique genotype, HERB-1, that persisted for over 50 years. HERB-1 is distinct from all examined modern strains, but it is a close relative of US-1, which replaced it outside of Mexico in the 20th century. We propose that HERB-1 and US-1 emerged from a metapopulation that was established in the early 1800s outside of the species' center of diversity. DOI:http://dx.doi.org/10.7554/eLife.00731.001.
There is increasing evidence that holocarpic oomycetes, i.e., those converting their entire vegetative thallus into zoospores upon maturation, are a phylogenetically diverse group in both freshwater ...and marine ecosystems. Most of the known holocarpic oomycete species diverge before the main split of
and
and are, thus, termed as early-diverging oomycetes. In environmental sequencing studies, it was revealed that of the early-diverging genera especially
,
, and
are widespread. As in these studies especially the Arctic Ocean seemed to harbor many undiscovered species, sampling was conducted at the Blávík research station on Fáskrúðsfjörður in the East Fjords of Iceland, where there is both an influence from the Arctic Ocean and the North Atlantic. During the screening for infected diatoms, a parasitoid was found in the marine diatom genus
, which is one of the most abundant genera in arctic ecosystems. Molecular phylogenetics and morphological characterization revealed that the parasitoid belonged to the genus
and corresponded to one of the lineages previously found in single-cell sequencing. Thus, the current study both contributes to the knowledge of the genus
and the increasing diversity of the genus suggests that the many linages found in environmental sequencing which can still not be associated with known species might represent actual species to be discovered in future studies.
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Lagena
has so far only been known from the scarcely reported but widespread species
Lagena radicicola
, which is a parasite of root epidermal cells. While it was mostly reported from a wide range of ...cereals and other grasses, it has been shown to affect some dicot species under, e.g. tobacco and sugar beet. Due to the wide host spectrum under laboratory conditions, there were no attempts to subdivide the genus into several species, even though some morphological differentiation was reported and the species had been found in several continents. During a survey of diatoms, we came across some parasitoids that would have previously been assumed to be members of the genus
Lagenidium
. The species exhibited rather narrow host specificity in nature. One species was brought into dual culture with host diatoms of the genus
Ulnaria
, but could not be transferred to other host genera. Surprisingly, phylogenetic analyses revealed that
Lagena radicicola
was in a sister clade to that formed by the diatom parasitoids, suggesting a versatile pathogenicity of the genus. Interestingly, several phylogenetic lineages only known from environmental sequencing were clustered with the species found in this study, hinting an undiscovered diversity in the genus
Lagena
.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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