Deciphering Aphanomyces euteiches-pea-biocontrol bacterium interactions through untargeted metabolomics

Aphanomyces euteiches causes root rot in pea, leading to significant yield losses. However, the metabolites involved in this pathosystem have not been thoroughly studied. This study aimed to fill this gap and explore mechanisms of bacterial suppression of A. euteiches via untargeted metabolomics using pea grown in a controlled environment. Chemical isotope labeling (CIL), followed by liquid chromatography-mass spectrometry (LC-MS), was used for metabolite separation and detection. Univariate and multivariate analyses showed clear separation of metabolites from pathogen-treated pea roots and roots from other treatments. A three-tier approach positively or putatively identified 5249 peak pairs or metabolites. Of these, 403 were positively identified in tier 1; 940 were putatively identified with high confidence in tier 2. There were substantial changes in amino acid pool, and fatty acid and phenylpropanoid pathway products. More metabolites, including salicylic and jasmonic acids, were upregulated than downregulated in A. euteiches-infected roots. 1-aminocyclopropane-1-carboxylic acid and 12-oxophytodienoic acid were upregulated in A. euteiches + bacterium-treated roots compared to A. euteiches-infected roots. A great number of metabolites were up- or down-regulated in response to A. euteiches infection compared with the control and A. euteiches + bacterium-treated plants. The results of this study could facilitate improved disease management.

The functional role of Daphnia in the host-pathogen interaction of crayfish and the crayfish plague disease agent (Aphanomyces astaci)

Pathogen spores have been recognized as prey with implications for resource dynamics, energy transfer and disease transmission. In aquatic ecosystems, filter-feeders are able to consume such motile forms of pathogens that can cause severe disease in susceptible hosts. The interactions between European crayfish and the crayfish plague pathogen Aphanomyces astaci are of particular conservation interest. In this study, we aim to evaluate the ecological interactions between Ap. astaci, its host Astacus astacus and individuals of the genus Daphnia, filter-feeding planktonic crustaceans. Our focus was on the consumption of the motile zoospores by Daphnia individuals, but we also considered the potential of Daphnia as non-target hosts. We conducted a series of infection and life-history experiments with Ap. astaci, three Daphnia species (D. magna, D. galeata, and D. pulex) and the noble crayfish As. astacus. We did not observe any lethal effects in the infection experiments involving Ap. astaci and Daphnia. Only D. pulex showed differences in some life-history traits. The feeding experiment using the motile zoospores of Ap. astaci as alternative food source or as supplement to different amounts of algal food revealed their nutritional value: D. magna individuals survived, grew, and reproduced on a zoospore diet alone. When zoospores were supplemented to the regular algal diet, all life-history parameters have been significantly improved. However, this successful consumption of zoospores did not result in a reduced mortality of the susceptible crayfish As. astacus during the infection experiment. Nevertheless, the pathogen load of Ap. astaci in the tissues of As. astacus was significantly reduced as a consequence of the feeding activity of Daphnia. Our results indicate that an abundant filter-feeding community can reduce the amount of infective zoospores in the water body and thus be beneficial to susceptible crayfish hosts, potentially acting as a general buffer against zoospore-transmitted diseases in lentic waters.

Fine mapping of Ae-Ps4.5, a major locus for resistance to pathotype III of Aphanomyces euteiches in pea

KEY MESSAGE

QTL mapping and recombinant screening confirmed the major effect of QTL Ae-Ps4.5 on pea resistance to pathotype III of Aphanomyces euteiches and fine-mapped the QTL to a 3.06-Mb interval. Aphanomyces root rot, caused by Aphanomyces euteiches, is the most important disease of pea (Pisum sativum L.) worldwide. The development of pea-resistant varieties is a major challenge to control the disease. Previous linkage studies identified seven main resistance quantitative trait loci (QTL), including the QTL Ae-Ps4.5 associated with partial resistance in US nurseries infested by the pea pathotype III of A. euteiches. This study aimed to confirm the major effect of Ae-Ps4.5 on A. euteiches pathotype III, refine its interval, and identify candidate genes underlying the QTL. QTL mapping on an updated genetic map from the Puget × 90-2079 pea recombinant inbred line population identified Ae-Ps4.5 in a 0.8-cM confidence interval with a high effect (R2 = 89%) for resistance to the Ae109 reference strain of A. euteiches (pathotype III) under controlled conditions. However, the QTL mapping did not detect Ae-Ps4.5 for resistance to the RB84 reference strain of A. euteiches (pathotype I). Screening 224-pea BC5F2 plant progeny derived from three near-isogenic lines (NILs) carrying the 90-2079 allele at Ae-Ps4.5 in the Puget genetic background with 26 SNP markers identified 15 NILs showing recombination in the QTL interval. Phenotyping of the recombinant lines for resistance to the Ae109 strain of A. euteiches reduced the QTL to a physical interval of 3.06 Mb, containing 50 putative annotated genes on the Caméor pea genome V1a among which three candidate genes highlighted. This study provides closely linked SNP markers and putative candidate genes to accelerate pea breeding for resistant varieties to Aphanomyces root rot.

Protocols for studying the crayfish plague pathogen, Aphanomyces astaci, and its host-pathogen interactions

The crayfish plague caused by the pathogen Aphanomyces astaci has decimated the European and Asian populations of freshwater crayfish and represents an important threat to the other highly susceptible crayfish species in the world, such as the Australian, Madagascar, and South American species. The development and application of molecular methods addressed to the identification of A. astaci has increased exponentially during the last decades in contrast to a slow trend of the pathogen biology and host interaction. There is still a need for a better comprehension of the A. astaci-crayfish interactions, specifically the resistance and tolerance immune mechanism. These types of studies required a robust basic knowledge on the developmental biology of the pathogen in order to reproduce life stages and to perform infection experiments. A great piece of work in this area was carried out during the 1960 s to 80 s in University of Uppsala. Thus, the purpose of this work was to update previous protocols as well as to generate new guidelines to reproduce key developmental biology stages of A. astaci, to eventually identify crayfish populations with higher resistance and tolerance to this pathogen. This work also refers to other methodologies and guidelines for the diagnosis of crayfish plague, the pathogen isolation, and the in vitro production of zoospores.

Epidemiology of epizootic ulcerative syndrome (EUS) in fish in the main water bodies of the Kavango-Zambezi and Great Limpopo transfrontier conservation areas of Zimbabwe

A three-year study investigated the epidemiology of epizootic ulcerative syndrome (EUS) in fish from Kavango-Zambezi (KAZA) and Great Limpopo (GL) transfrontier conservation areas of Zimbabwe. A total of 38 sites comprising 27 wild fisheries and 11 aquacultures, from Mashonaland West, Matabeleland North and South, and Midlands were selected. Of the 27 wild fisheries, EUS-positive fish were detected from 9 (33.3%) and none from the 11 aquacultures. No positive cases were detected from Nile tilapia (Oreochromis niloticus) from both aquacultures and wild fisheries. A total of 9.9% (239/2423) fish from the nine positive fisheries had typical EUS lesions, and infection was confirmed in 15 species. Prevalence was significantly higher (p < 0.05) in KAZA (11.5%; 95% CI: 9.6-13.4) compared with GL (8.6%; 95% CI: 7.1-10.1). The most affected were Clarias, followed by Barbus and Oreochromis species. Most cases (>80%) were reported in winter when ambient temperature was low. Further studies are required to determine water parameters associated with EUS outbreaks. These results suggested that the African sharptooth catfish (Clarias gariepinus) could be used potentially as an indicator species for EUS surveillance programmes. Thus, implementation of surveillance and biosecurity programmes that take into consideration the epidemiology of EUS will be beneficial.

Anti-Cancer and Anti-Inflammatory Activities of a Short Molecule, PS14 Derived from the Virulent Cellulose Binding Domain of Aphanomyces invadans, on Human Laryngeal Epithelial Cells and an In Vivo Zebrafish Embryo Model

In this study, the anti-cancer and anti-inflammatory activities of PS14, a short peptide derived from the cellulase binding domain of pathogenic fungus, Aphanomyces invadans, have been evaluated, in vitro and in vivo. Bioinformatics analysis of PS14 revealed the physicochemical properties and the web-based predictions, which indicate that PS14 is non-toxic, and it has the potential to elicit anti-cancer and anti-inflammatory activities. These in silico results were experimentally validated through in vitro (L6 or Hep-2 cells) and in vivo (zebrafish embryo or larvae) models. Experimental results showed that PS14 is non-toxic in L6 cells and the zebrafish embryo, and it elicits an antitumor effect Hep-2 cells and zebrafish embryos. Anticancer activity assays, in terms of MTT, trypan blue and LDH assays, showed a dose-dependent inhibitory effect on cell proliferation. Moreover, in the epithelial cancer cells and zebrafish embryos, the peptide challenge (i) caused significant changes in the cytomorphology and induced apoptosis; (ii) triggered ROS generation; and (iii) showed a significant up-regulation of anti-cancer genes including BAX, Caspase 3, Caspase 9 and down-regulation of Bcl-2, in vitro. The anti-inflammatory activity of PS14 was observed in the cell-free in vitro assays for the inhibition of proteinase and lipoxygenase, and heat-induced hemolysis and hypotonicity-induced hemolysis. Together, this study has identified that PS14 has anti-cancer and anti-inflammatory activities, while being non-toxic, in vitro and in vivo. Future experiments can focus on the clinical or pharmacodynamics aspects of PS14.

Impact of cinnamaldehyde on innate immunity and immune gene expression in Channa striatus against Aphanomyces invadans

The effect of cinnamaldehyde (CM) enriched diet on immunity and cytokine gene expression in Channa striatus against Aphanomyces invadans is reported. C. striatus was uniformly divided into eight groups (n = 25 fish each) and fed with formulated diets with 0, 5, 10, and 15 mg kg^-1 CM enriched diet. In healthy and infected groups fed with 5 mg kg^-1 diet the leukocytes count increased significantly after 4th week; with 10 mg kg^-1 CM diet the increase manifested after 6th week, but with 15 mg kg^-1 not even after 8th week. In both groups, 5 mg kg^-1 CM diet resulted in a significant increase in the serum total protein, albumin, and globulin levels after 4th week, whereas with other diets this effect was observed only after 6th week. Similarly, with any enriched diet the lysozyme activity increased significantly, but with 15 mg kg^-1 CM diet only after 6th week. In both groups the complement activity and lymphocyte production increased significantly when fed with 5 mg kg^-1 CM diet after 4th week while with other enriched diets only after 6th week. The phagocytic activity increased significantly in both groups fed with 5 mg kg^-1 CM diet after 6th week, whereas the SOD activity increased after 4th week. The IgM production increased significantly in both groups fed with 5 mg kg^-1 CM diet after 2nd week, while with 5 and 10 mg kg^-1 CM diet after 4th week. In both groups, the expression of CXCR3α was significant on 4th week when fed with 10 mg kg^-1 CM diet, while in the healthy group fed with 15 mg kg^-1 CM diet the expression manifested earlier than 4th week. However, when fed with 10 and 15 mg kg^-1 CM diets the increase was observed on 6th week; whereas, the expression of MHC-I reached the maximum on 6th week with any enriched diet. The results indicate that in C. striatus the innate immunity and expression of cytokine and immune related genes were significantly modulated when fed with 5 mg kg^-1 CM diet on 4th week against A. invadans.

Toxic effects in Aphanomyces brasiliensis and zebrafish embryos caused by oomyceticides

In fish farming, high losses occur during egg incubation and larviculture due to diseases caused by oomycetes. This study aimed to identify the oomycete species that occurs in zebrafish Danio rerio eggs and to evaluate the oomyceticidal effect of copper sulfate, bronopol and methylene blue on the mycelial growth of this organism, as well as to determine the lethal and sublethal toxicity of these compounds in embryos of D. rerio. The isolates were cultivated in yeast-starch medium to determine the concentration necessary to inhibit mycelial growth by 50% (IC50) and 100% (minimum oomyceticidal concentration) after a 96 h exposure to these compounds. In addition, tests with D. rerio eggs were conducted to determine the lethal concentrations for 50% of the organisms (96h-LC50), and the concentrations that inhibited 17% of the eggs hatching (96h-IC17) after 96 h. The organism responsible for the mortality of D. rerio eggs was classified by classical and molecular methods as Aphanomyces brasiliensis, representing the first report of this pathogen in zebrafish eggs. IC50 values could be determined for both bronopol and copper sulfate, whereas methylene blue had low effectiveness against the oomycete. Copper showed high toxicity to D. rerio eggs at low concentrations, while methylene blue and bronopol toxicity was low and similar to each other. The use of bronopol at a concentration of 4.8 mg l-1 for the treatment of zebrafish eggs allows controlling the pathology without causing deleterious effects to the treated organisms.

First record of epizootic ulcerative syndrome from the Upper Congo catchment: An outbreak in the Bangweulu swamps, Zambia

We report on the first outbreak of epizootic ulcerative syndrome (EUS) amongst wild fish populations in the Bangweulu swamps, an inland delta, in the north of Zambia during 2014. The area supports a large and diverse fish fauna related to, but distinct from, that of the Zambezi River system where EUS outbreaks have occurred since 2006. A sizeable artisanal fishery, based on extensive fish weirs, is sustained by the annual flooding of the swamps, and observations of the disease outbreak by fishermen were recorded. Signs typical of infection with Aphanomyces invadans were observed in a number of species. Clinical observations, histology and molecular diagnostic methods were used to confirm infection with A. invadans in two of the most commonly and severely affected species. Several features of the wetland may have contributed to the outbreak and the annual recurrence of the disease. Modes by which the disease may have been introduced into the swamps are discussed. The outbreak is of great significance as the Bangweulu swamps drain into the Congo River in neighbouring Democratic Republic of Congo, Africa's largest drainage system with an extensive and diverse fish fauna previously unaffected by EUS.

Genome-wide association mapping of partial resistance to Aphanomyces euteiches in pea

BACKGROUND

Genome-wide association (GWA) mapping has recently emerged as a valuable approach for refining the genetic basis of polygenic resistance to plant diseases, which are increasingly used in integrated strategies for durable crop protection. Aphanomyces euteiches is a soil-borne pathogen of pea and other legumes worldwide, which causes yield-damaging root rot. Linkage mapping studies reported quantitative trait loci (QTL) controlling resistance to A. euteiches in pea. However the confidence intervals (CIs) of these QTL remained large and were often linked to undesirable alleles, which limited their application in breeding. The aim of this study was to use a GWA approach to validate and refine CIs of the previously reported Aphanomyces resistance QTL, as well as identify new resistance loci.

METHODS

A pea-Aphanomyces collection of 175 pea lines, enriched in germplasm derived from previously studied resistant sources, was evaluated for resistance to A. euteiches in field infested nurseries in nine environments and with two strains in climatic chambers. The collection was genotyped using 13,204 SNPs from the recently developed GenoPea Infinium® BeadChip.

RESULTS

GWA analysis detected a total of 52 QTL of small size-intervals associated with resistance to A. euteiches, using the recently developed Multi-Locus Mixed Model. The analysis validated six of the seven previously reported main Aphanomyces resistance QTL and detected novel resistance loci. It also provided marker haplotypes at 14 consistent QTL regions associated with increased resistance and highlighted accumulation of favourable haplotypes in the most resistant lines. Previous linkages between resistance alleles and undesired late-flowering alleles for dry pea breeding were mostly confirmed, but the linkage between loci controlling resistance and coloured flowers was broken due to the high resolution of the analysis. A high proportion of the putative candidate genes underlying resistance loci encoded stress-related proteins and others suggested that the QTL are involved in diverse functions.

CONCLUSION

This study provides valuable markers, marker haplotypes and germplasm lines to increase levels of partial resistance to A. euteiches in pea breeding.

A novel murrel Channa striatus mitochondrial manganese superoxide dismutase: gene silencing, SOD activity, superoxide anion production and expression

We have reported the molecular characterization including gene silencing, superoxide activity, superoxide anion production, gene expression and molecular characterization of a mitochondrial manganese superoxide dismutase (mMnSOD) from striped murrel Channa striatus (named as CsmMnSOD). The CsmMnSOD polypeptide contains 225 amino acids with a molecular weight of 25 kDa and a theoretical isoelectric point of 8.3. In the N-terminal region, CsmMnSOD carries a mitochondrial targeting sequence and a superoxide dismutases (SOD) Fe domain (28-109), and in C-terminal region, it carries another SOD Fe domain (114-220). The CsmMnSOD protein sequence shared significant similarity with its homolog of MnSOD from rock bream Oplegnathus fasciatus (96%). The phylogenetic analysis showed that the CsmMnSOD fell in the clade of fish mMnSOD group. The monomeric structure of CsmMnSOD possesses 9 α-helices (52.4%), 3 β-sheets (8.8%) and 38.8% random coils. The highest gene expression was noticed in liver, and its expression was inducted with fungal (Aphanomyces invadans) and bacterial (Aeromonas hydrophila) infections. The gene silencing results show that the fish that received dsRNA exhibited significant (P < 0.05) changes in expression when compared to their non-injected and fish physiological saline-injected controls. The SOD activity shows that the activity increases with the spread of infection and decreases once the molecule controls the pathogen. The capacity of superoxide anion production was determined by calculating the granular blood cell count during infection in murrel. It shows that the infection influenced the superoxide radical production which plays a major role in killing the pathogens. Overall, this study indicated the defense potentiality of CsmMnSOD; however, further research is necessary to explore its capability at protein level.

Effects of climate change, invasive species, and disease on the distribution of native European crayfishes

Climate change will require species to adapt to new conditions or follow preferred climates to higher latitudes or elevations, but many dispersal-limited freshwater species may be unable to move due to barriers imposed by watershed boundaries. In addition, invasive nonnative species may expand into new regions under future climate conditions and contribute to the decline of native species. We evaluated future distributions for the threatened European crayfish fauna in response to climate change, watershed boundaries, and the spread of invasive crayfishes, which transmit the crayfish plague, a lethal disease for native European crayfishes. We used climate projections from general circulation models and statistical models based on Mahalanobis distance to predict climate-suitable regions for native and invasive crayfishes in the middle and at the end of the 21st century. We identified these suitable regions as accessible or inaccessible on the basis of major watershed boundaries and present occurrences and evaluated potential future overlap with 3 invasive North American crayfishes. Climate-suitable areas decreased for native crayfishes by 19% to 72%, and the majority of future suitable areas for most of these species were inaccessible relative to native and current distributions. Overlap with invasive crayfish plague-transmitting species was predicted to increase. Some native crayfish species (e.g., noble crayfish [Astacus astacus]) had no future refugia that were unsuitable for the modeled nonnative species. Our results emphasize the importance of preventing additional introductions and spread of invasive crayfishes in Europe to minimize interactions between the multiple stressors of climate change and invasive species, while suggesting candidate regions for the debatable management option of assisted colonization.

An experimental system to study responses of Medicago truncatula roots to chitin oligomers of high degree of polymerization and other microbial elicitors

A fully acetylated, soluble CO preparation of mean DP of ca. 7 was perceived with high sensitivity by M. truncatula in a newly designed versatile root elicitation assay. The root system of legume plants interacts with a large variety of microorganisms, either pathogenic or symbiotic. Understanding how legumes recognize and respond specifically to pathogen-associated or symbiotic signals requires the development of standardized bioassays using well-defined preparations of the corresponding signals. Here we describe the preparation of chitin oligosaccharide (CO) fractions from commercial chitin and their characterization by a combination of liquid-state and solid-state nuclear magnetic resonance spectroscopy. We show that the CO fraction with highest degree of polymerization (DP) became essentially insoluble after lyophilization. However, a fully soluble, fully acetylated fraction with a mean DP of ca. 7 was recovered and validated by showing its CERK1-dependent activity in Arabidopsis thaliana. In parallel, we developed a versatile root elicitation bioassay in the model legume Medicago truncatula, using a hydroponic culture system and the Phytophthora β-glucan elicitor as a control elicitor. We then showed that M. truncatula responded with high sensitivity to the CO elicitor, which caused the production of extracellular reactive oxygen species and the transient induction of a variety of defense-associated genes. In addition, the bioassay allowed detection of elicitor activity in culture filtrates of the oomycete Aphanomyces euteiches, opening the way to the analysis of recognition of this important legume root pathogen by M. truncatula.

Potent infection reservoir of crayfish plague now permanently established in Norway

Noble crayfish Astacus astacus is threatened in Europe due to invasive crayfish carrying the crayfish plague agent Aphanomyces astaci. Norway is among the last countries in which the introduction of non-indigenous crayfish has been limited through strict legislation practices. However, North American signal crayfish Pacifastacus leniusculus were recently discovered in a water-course that has been repeatedly hit by the plague. We mapped the distribution and relative density (catch per unit effort) of signal crayfish within this lake, and performed agent-specific real-time PCR to estimate the prevalence of A. astaci in the population. The resulting length frequencies and relative density estimates clearly demonstrate a well-established signal crayfish population, in which 86.4% of the analysed individuals were confirmed carriers. The success of detection was significantly higher (84.1%) in the crayfish tailfan (i.e. uropods) than in the soft abdominal cuticle (38.4%), which is commonly used in prevalence studies. We therefore propose tailfan (uropods and telson) as the preferred tissue for studying A. astaci prevalence in signal crayfish populations. The likelihood of detecting an A. astaci-positive signal crayfish increased significantly with increasing crayfish length. Further, large female crayfish expressed significantly higher PCR-forming units values than large males. In surveys primarily exploring the presence of A. astaci-positive individuals in a population, large females should be selected for molecular analyses. Our study demonstrates that a potent crayfish plague infection reservoir, evidently originating from the illegal human introduction of signal crayfish, has permanently been established in Norway.

in sugar beet

Aphanomyces root rot, caused by Aphanomyces cochlioides Drechs., is one of the most serious diseases of sugar beet (Beta vulgaris L.). Identification and characterization of resistance genes is a major task in sugar beet breeding. To ensure the effectiveness of marker-assisted screening for Aphanomyces root rot resistance, genetic analysis of mature plants' phenotypic and molecular markers' segregation was carried out. At a highly infested field site, some 187 F(2) and 66 F(3) individuals, derived from a cross between lines 'NK-310mm-O' (highly resistant) and 'NK-184mm-O' (susceptible), were tested, over two seasons, for their level of resistance to Aphanomyces root rot. This resistance was classified into six categories according to the extent and intensity of whole plant symptoms. Simultaneously, two selected RAPD and 159 'NK-310mm-O'-coupled AFLP were used in the construction of a linkage map of 695.7 cM. Each of nine resultant linkage groups was successfully anchored to one of nine sugar beet chromosomes by incorporating 16 STS markers. Combining data for phenotype and molecular marker segregation, a single QTL was identified on chromosome III. This QTL explained 20% of the variance in F(2) population (in the year 2002) and 65% in F(3) lines (2003), indicating that this QTL plays a major role in the Aphanomyces root rot resistance. This is the first report of the genetic mapping of resistance to Aphanomyces-caused diseases in sugar beet.

Infection experiments with Aphanomyces invadans in four species of estuarine fish

Along the eastern seaboard of the US, Atlantic menhaden, Brevoortia tyrannus, develop characteristic ulcerative lesions, a condition termed ulcerative mycosis. These lesions are identical to those seen across Asia in fish affected by epizootic ulcerative syndrome, a condition caused by the fungus-like oomycete Aphanomyces invadans. Young-of-the-year menhaden inhabiting estuarine environments are the primary species affected in the USA and little is known about the factors involved in the initiation of the lesions, or why menhaden are predominantly infected. Atlantic menhaden, hogchoker, Trinectus maculatus, striped killifish, Fundulus majalis, and mummichog, Fundulus heteroclitus, were inoculated with A. invadans (80 zoospores per fish) to explore species differences in infection and lesion development. All four species developed lesions. Killifish developed frank lesions similar to those observed in menhaden but the gross lesions occurred later, approximately 5-10 days after those on menhaden. Hogchoker and mummichog did not develop gross skin ulcers; rather, their lesions appeared as reddened areas under the epidermis. Mummichogs also showed evidence of significant healing with a well-developed granuloma and significant myocyte regeneration. These experiments show that species barriers as well as ecological barriers can explain some of the factors involved in the development of lesions in, and specificity of the water mould for, menhaden.