Search Results (9)

Soil seedbanks are particularly important for the resiliency of species living in habitats threatened by climate change, such as alpine meadows. We investigated the germination rate and seedbank potential for the endemic species Dianthus pavonius, a carnation native to the Maritime Alps that is used as model system for disease in natural populations due to its frequent infections by a sterilizing anther-smut pathogen. We aimed to ascertain whether this species can create a persistent reserve of viable seeds in the soil which could impact coevolutionary dynamics. Over three years, we collected data from seeds sown in natural soil and analyzed their germination and viability. We found that D. pavonius seeds are not physiologically dormant and they are able to create a persistent soil seed bank that can store seeds in the soil for up to three years, but lower than the estimated plant lifespan. We conclude that while the seedbank may provide some demographic stability to the host population, its short duration is unlikely to strongly affect the host’s ability to respond to selection from disease. Our findings have implications for the conservation of this alpine species and for understanding the evolutionary dynamics between the host and its pathogen. Full article

Microbotryum lychnidis-dioicae is an obligate fungal species colonizing the plant host, Silene latifolia. The fungus synthesizes and secretes effector proteins into the plant host during infection to manipulate the host for completion of the fungal lifecycle. The goal of this study was to continue functional characterization of such M. lychnidis-dioicae effectors. Here, we identified three putative effectors and their putative host-plant target proteins. MVLG_02245 is highly upregulated in M. lychnidis-dioicae during infection; yeast two-hybrid analysis suggests it targets a tubulin α-1 chain protein ortholog in the host, Silene latifolia. A potential plant protein interacting with MVLG_06175 was identified as CASP-like protein 2C1 (CASPL2C1), which facilitates the polymerization of the Casparian strip at the endodermal cells. Proteins interacting with MVLG_05122 were identified as CSN5a or 5b, involved in protein turnover. Fluorescently labelled MVLG_06175 and MVLG_05122 were expressed in the heterologous plant, Arabidopsis thaliana. MVLG_06175 formed clustered granules at the tips of trichomes on leaves and in root caps, while MVLG_05122 formed a band structure at the base of leaf trichomes. Plants expressing MVLG_05122 alone were more resistant to infection with Fusarium oxysporum. These results indicate that the fungus might affect the formation of the Casparian strip in the roots and the development of trichomes during infection as well as alter plant innate immunity. Full article

Smut fungi represent a large group of biotrophic plant pathogens that cause extensive yield loss and are also model organisms for studying plant–pathogen interactions. In recent years, they have become biotechnological tools. After initial penetration of the plant epidermis, smut fungi grow intra—and intercellularly without disrupting the plant-plasma membrane. Following the colonialization step, teliospores are formed and later released. While some smuts only invade the tissues around the initial penetration site, others colonize in multiple plant organs resulting in spore formation distal from the original infection site. The intimate contact zone between fungal hyphae and the host is termed the biotrophic interaction zone and enables exchange of signals and nutrient uptake. Obviously, all steps of on and in planta growth require fine sensing of host conditions as well as reprogramming of the host by the smut fungus. In this review, we highlight selected examples of smut fungal colonization styles, directional growth in planta, induction of spore formation, and the signals required, pointing to excellent reviews for details, to draw attention to some of the open questions in this important research field. Full article

Mitochondria are important organelles in eukaryotes that provide energy for cellular processes. Their function is highly conserved and depends on the expression of nuclear encoded genes and genes encoded in the organellar genome. Mitochondrial DNA replication is independent of the replication control of nuclear DNA and as such, mitochondria may behave as selfish elements, so they need to be controlled, maintained and reliably inherited to progeny. Phytopathogenic fungi meet with special environmental challenges within the plant host that might depend on and influence mitochondrial functions and services. We find that this topic is basically unexplored in the literature, so this review largely depends on work published in other systems. In trying to answer elemental questions on mitochondrial functioning, we aim to introduce the aspect of mitochondrial functions and services to the study of plant-microbe-interactions and stimulate phytopathologists to consider research on this important organelle in their future projects. Full article

(1) Background: Silene latifolia is a dioecious plant, whose sex is determined by XY-type sex chromosomes. Microbotryum lychnidis-dioicae is a smut fungus that infects S. latifolia plants and causes masculinization in female flowers, as if Microbotryum were acting as a sex-determining gene. Recent large-scale sequencing efforts have promised to provide candidate genes that are involved in the sex determination machinery in plants. These candidate genes are to be analyzed for functional characterization. A virus vector can be a tool for functional gene analyses; (2) Methods: To develop a viral vector system in S. latifolia plants, we selected Apple latent spherical virus (ALSV) as an appropriate virus vector that has a wide host range; (3) Results: Following the optimization of the ALSV inoculation method, S. latifolia plants were infected with ALSV at high rates in the upper leaves. In situ hybridization analysis revealed that ALSV can migrate into the flower meristems in S. latifolia plants. Successful VIGS (virus-induced gene silencing) in S. latifolia plants was demonstrated with knockdown of the phytoene desaturase gene. Finally, the developed method was applied to floral organ genes to evaluate its usability in flowers; (4) Conclusion: The developed system enables functional gene analyses in S. latifolia plants, which can unveil gene functions and networks of S. latifolia plants, such as the mechanisms of sex determination and fungal-induced masculinization. Full article

Microbotryum silybum, a smut fungus, is studied as an agent for the biological control of Silybum marianum (milk thistle) weed. Confirmation of the systemic infection is essential in order to assess the effectiveness of the biological control application and assist decision-making. Nonetheless, in situ diagnosis is challenging. The presently demonstrated research illustrates the identification process of systemically infected S. marianum plants by means of field spectroscopy and the multilayer perceptron/automatic relevance determination (MLP-ARD) network. Leaf spectral signatures were obtained from both healthy and infected S. marianum plants using a portable visible and near-infrared spectrometer (310–1100 nm). The MLP-ARD algorithm was applied for the recognition of the infected S. marianum plants. Pre-processed spectral signatures served as input features. The spectra pre-processing consisted of normalization, and second derivative and principal component extraction. MLP-ARD reached a high overall accuracy (90.32%) in the identification process. The research results establish the capacity of MLP-ARD to precisely identify systemically infected S. marianum weeds during their vegetative growth stage. Full article

(1) Background: Plant pathogenic fungi often display high levels of host specificity and biotrophic fungi; in particular, they must manipulate their hosts to avoid detection and to complete their obligate pathogenic lifecycles. One important strategy of such fungi is the secretion of small proteins that serve as effectors in this process. Microbotryum violaceum is a species complex whose members infect members of the Caryophyllaceae; M. lychnidis-dioicae, a parasite on Silene latifolia, is one of the best studied interactions. We are interested in identifying and characterizing effectors of the fungus and possible corresponding host targets; (2) Methods: In silico analysis of the M. lychnidis-dioicae genome and transcriptomes allowed us to predict a pool of small secreted proteins (SSPs) with the hallmarks of effectors, including a lack of conserved protein family (PFAM) domains and also localized regions of disorder. Putative SSPs were tested for secretion using a yeast secretion trap method. We then used yeast two-hybrid analyses for candidate-secreted effectors to probe a cDNA library from a range of growth conditions of the fungus, including infected plants; (3) Results: Roughly 50 SSPs were identified by in silico analysis. Of these, 4 were studied further and shown to be secreted, as well as examined for potential host interactors. One of the putative effectors, MVLG_01732, was found to interact with Arabidopsis thaliana calcium-dependent lipid binding protein (AtCLB) and with cellulose synthase interactive protein 1 orthologues; and (4) Conclusions: The identification of a pool of putative effectors provides a resource for functional characterization of fungal proteins that mediate the delicate interaction between pathogen and host. The candidate targets of effectors, e.g., AtCLB, involved in pollen germination suggest tantalizing insights that could drive future studies. Full article

Dioecious plants in the Caryophyllaceae family are susceptible to infection by members of the anthericolous smut fungi. In our studies of the Silene latifolia/Microbotryum lychnidis-dioicae pathosystem, we were interested in characterizing the plant-pathogen interaction at the molecular level before and during teliosporogenesis. This takes place during floral bud development, and we hoped to capture the interaction by Illumina Next-Gen RNA-Sequencing. Using previous literature that documented the stages of the floral buds for S. latifolia, we examined the floral buds from plants grown and infected under growth chamber conditions, using the disserting microscope to determine the stage of floral buds based on the morphology. We compiled the information and determined the size of floral buds that correspond to the desired stages of development for tissue collection, for the purpose of RNA-sequencing. This offers a practical approach for researchers who require a large number of floral buds/tissue categorized by stages of development, ascertaining whether infected/uninfected buds are at comparable stages of development and whether this also holds true for male vs. female buds. We also document our experience in infecting the plants and some of the unusual morphologies we observed after infection. Full article

Seven new polyoxygenated steroids (1–7) were isolated together with seven known analogues (8–14) from the South China Sea soft coral, Sarcophyton sp. The structures of the new compounds were identified on the basis of extensive spectroscopic analysis and comparison with reported data. All the steroids are characterized with 3β,5α,6β-hydroxy moiety, displaying carbon skeletons of cholestane, ergostane, gorgostane and 23,24-dimethyl cholestane. In the in vitro bioassay, metabolites exhibited different levels of antimicrobial activity against bacterial species Escherichia coli and Bacillus megaterium, and fungal species Microbotryum violaceum and Septoria tritici. No inhibition was detected towards microalga Chlorella fusca. Preliminary structure-activity analysis suggests that the 11α-acetoxy group may increase both antibacterial and antifungal activities. The terminal-double bond and the cyclopropane moiety at the side chain may also contribute to the bioactivity. Full article