Gene Network and Database for Genes of Wheat’s Resistance to Pathogenic Fungi

An overview describing a gene network that controls the formation of plant responses to diseases caused by pathogenic fungi (http://wwwmgs.bionet.nsc.ru/mgs/gnw/genenet//viewer/Plant%20fungus%20pathogen.html) is presented. The gene network represents the coordinated interactions of genes, proteins, and regulatory molecules, including integrated defense mechanisms that prevent the development of infection, localize the lesion, and minimize damage. The gene network was reconstructed on the basis of literature data, and the elements of the gene network were associated with the records of the PGR database (Pathogenesis-Related Genes, http://srs6.bionet.nsc.ru/srs6bin/cgi-bin/wgetz?-page+top+-newId), where information on plant genes resistant to pathogenic fungi is accumulated. Reconstruction of the gene network allows us to formalize, visualize, and systematize possible mechanisms for the response of plant cells to fungal infection, which may be useful for the planning of experiments and interpretation of experimental data in this field of science.     

Sharing of Diverse Mycorrhizal and Root-Endophytic Fungi among Plant Species in an Oak-Dominated Cool–Temperate Forest

Most terrestrial plants interact with diverse clades of mycorrhizal and root-endophytic fungi in their roots. Through belowground plant–fungal interactions, dominant plants can benefit by interacting with host-specific mutualistic fungi and proliferate in a community based on positive plant–mutualistic fungal feedback. On the other hand, subordinate plant species may persist in the community by sharing other sets (functional groups) of fungal symbionts with each other. Therefore, revealing how diverse clades of root-associated fungi are differentially hosted by dominant and subordinate plant species is essential for understanding plant community structure and dynamics. Based on 454-pyrosequencing, we determined the community composition of root-associated fungi on 36 co-occurring plant species in an oak-dominated forest in northern Japan and statistically evaluated the host preference phenotypes of diverse mycorrhizal and root-endophytic fungi. An analysis of 278 fungal taxa indicated that an ectomycorrhizal basidiomycete fungus in the genus Lactarius and a possibly endophytic ascomycete fungus in the order Helotiales significantly favored the dominant oak (Quercus) species. In contrast, arbuscular mycorrhizal fungi were generally shared among subordinate plant species. Although fungi with host preferences contributed to the compartmentalization of belowground plant–fungal associations, diverse clades of ectomycorrhizal fungi and possible root endophytes were associated not only with the dominant Quercus but also with the remaining plant species. Our findings suggest that dominant-ectomycorrhizal and subordinate plant species can host different subsets of root-associated fungi, and diverse clades of generalist fungi can counterbalance the compartmentalization of plant–fungal associations. Such insights into the overall structure of belowground plant–fungal associations will help us understand the mechanisms that facilitate the coexistence of plant species in natural communities.     

High Diversity and Low Specificity of Chaetothyrialean Fungi in Carton Galleries in a Neotropical Ant–Plant Association

New associations have recently been discovered between arboreal ants that live on myrmecophytic plants, and different groups of fungi. Most of the – usually undescribed – fungi cultured by the ants belong to the order Chaetothyriales (Ascomycetes). Chaetothyriales occur in the nesting spaces provided by the host plant, and form a major part of the cardboard-like material produced by the ants for constructing nests and runway galleries. Until now, the fungi have been considered specific to each ant species. We focus on the three-way association between the plant Tetrathylacium macrophyllum (Salicaceae), the ant Azteca brevis (Formicidae: Dolichoderinae) and various chaetothyrialean fungi. Azteca brevis builds extensive runway galleries along branches of T. macrophyllum. The carton of the gallery walls consists of masticated plant material densely pervaded by chaetothyrialean hyphae. In order to characterise the specificity of the ant–fungus association, fungi from the runway galleries of 19 ant colonies were grown as pure cultures and analyzed using partial SSU, complete ITS, 5.8S and partial LSU rDNA sequences. This gave 128 different fungal genotypes, 78% of which were clustered into three monophyletic groups. The most common fungus (either genotype or approximate species-level OTU) was found in the runway galleries of 63% of the investigated ant colonies. This indicates that there can be a dominant fungus but, in general, a wider guild of chaetothyrialean fungi share the same ant mutualist in Azteca brevis.     

Cell Cycle–Mediated Regulation of Plant Infection by the Rice Blast Fungus

To gain entry to plants, many pathogenic fungi develop specialized infection structures called appressoria. Here, we demonstrate that appressorium morphogenesis in the rice blast fungus Magnaporthe oryzae is tightly regulated by the cell cycle. Shortly after a fungus spore lands on the rice (Oryza sativa) leaf surface, a single round of mitosis always occurs in the germ tube. We found that initiation of infection structure development is regulated by a DNA replication-dependent checkpoint. Genetic intervention in DNA synthesis, by conditional mutation of the Never-in-Mitosis 1 gene, prevented germ tubes from developing nascent infection structures. Cellular differentiation of appressoria, however, required entry into mitosis because nimA temperature-sensitive mutants, blocked at mitotic entry, were unable to develop functional appressoria. Arresting the cell cycle after mitotic entry, by conditional inactivation of the Blocked-in-Mitosis 1 gene or expression of stabilized cyclinB-encoding alleles, did not impair appressorium differentiation, but instead prevented these cells from invading plant tissue. When considered together, these data suggest that appressorium-mediated plant infection is coordinated by three distinct cell cycle checkpoints that are necessary for establishment of plant disease.     

Clinical and Treatment Aspects of Brown–Black Fungi

Brown–black (or dematiaceous) fungi are responsible for a wide variety of infectious syndromes in both immunocompetent and immunocompromised patients, including local infections, allergic disease, pneumonia, brain abscess, and disseminated infection. They are distinct from the more common hyaline molds, Aspergillus and Fusarium, that cause human disease. They are often found in soil and generally distributed worldwide. In recent years, these fungi have been increasingly recognized as important pathogens. Dematiaceous fungi may have unique pathogenic mechanisms owing to the presence of melanin in their cell walls, which imparts the characteristic dark color to their spores and hyphae. Diagnosis rests on careful microscopic and pathologic examination, as there are no specific laboratory tests to reliably identify these fungi. Therapy depends upon the clinical syndrome, although disseminated infection often has high mortality. Triazoles such as voriconazole, posaconazole, and itraconazole are the most active antifungal agents available. Further studies are needed to better understand the pathogenesis and optimal treatment of these uncommon infections.     

Mathematical Modeling of the Dynamics of Plant Mineral Nutrition in the Fertilizer–Soil–Plant System

A numerical simulation of the spatial–temporal dynamics of a multi-parameter system has been developed. The components of this system are plant biomass, the mobile and stationary forms of mineral nutrition elements, rhizosphere microorganisms, and environmental parameters (temperature, humidity, and acidity). Parametric identification and verification of the adequacy of the model were carried out based on the experimental data on the growth of Krasnoufimskaya-100 spring wheat on peat lowland soil. The results are represented by temporal distributions of biomass from agricultural crops and the findings on the contents of the main nutrition elements within the plant (nitrogen, phosphorus, and potassium). An agronomic assessment and interpretation of the results are given.

     

Induction of Plant Defense Enzymes and Phenolics by Treatment With Plant Growth–Promoting Rhizobacteria Serratia marcescens NBRI1213

In greenhouse experiments, plant growth–promoting rhizobacteria (PGPR) Serratia marcescens NBRI1213 was evaluated for plant growth promotion and biologic control of foot and root rot of betelvine caused by Phytophthora nicotianae. Bacterization of betelvine (Piper betle L.) cuttings with S. marcescens NBRI1213 induced phenylalanine ammonia-lyase, peroxidase, and polyphenoloxidase activities in leaf and root. Qualitative and quantitative estimation of phenolic compounds was done through high-performance liquid chromatography (HPLC) in leaf and root of betelvine after treatment with S. marcescens NBRI1213 and infection by P. nicotianae. Major phenolics detected were gallic, protocatechuic, chlorogenic, caffeic, ferulic, and ellagic acids by comparison of their retention time with standards through HPLC. In all of the treated plants, synthesis of phenolic compounds was enhanced compared with control. Maximum accumulation of phenolics was increased in S. marcescens NBRI1213–treated plants infected with P. nicotianae. In a greenhouse test, bacterization using S. marcescens NBRI1213 decreased the number of diseased plants compared with nonbacterized controls. There were significant growth increases in shoot length, shoot dry weight, root length, and root dry weight, averaging 81%, 68%, 152%, and 290%, respectively, greater than untreated controls. This is the first report of PGPR–mediated induction of phenolics for biologic control and their probable role in protecting betelvine against P. nicotianae, an important soil-borne phytopathogenic fungus.     

Plant–microbe networks in soil are weakened by century-long use of inorganic fertilizers

Understanding the changes in plant–microbe interactions is critically important for predicting ecosystem functioning in response to human-induced environmental changes such as nitrogen (N) addition. In this study, the effects of a century-long fertilization treatment (> 150 years) on the networks between plants and soil microbial functional communities, detected by GeoChip, in grassland were determined in the Park Grass Experiment at Rothamsted Research, UK. Our results showed that plants and soil microbes have a consistent response to long-term fertilization—both richness and diversity of plants and soil microbes are significantly decreased, as well as microbial functional genes involved in soil carbon (C), nitrogen (N) and phosphorus (P) cycling. The network-based analyses showed that long-term fertilization decreased the complexity of networks between plant and microbial functional communities in terms of node numbers, connectivity, network density and the clustering coefficient. Similarly, within the soil microbial community, the strength of microbial associations was also weakened in response to long-term fertilization. Mantel path analysis showed that soil C and N contents were the main factors affecting the network between plants and microbes. Our results indicate that century-long fertilization weakens the plant–microbe networks, which is important in improving our understanding of grassland ecosystem functions and stability under long-term agriculture management.     

Prey Habitat Location by the Cassava Mealybug Predator Exochomus flaviventris: Olfactory Responses to Odor of Plant, Mealybug, Plant–Mealybug Complex, and Plant–Mealybug–Natural Enemy Complex

Exochomus flaviventris Mader is considered to be the most active predator of the cassava mealybug Phenacoccus manihoti Matile–Ferrero in Central Africa. The response of experienced gravid female coccinellids to the odor of cassava plant (var. Zanaga), unparasitized mealybugs, plant–mealybug complex with or without feeding prey (parasitized or not), and plant–mealybug complex with or without conspecific coccinellids was investigated in a Y-tube olfactometer. The odor of uninfested cassava plants was not more attractive than clean air. Dual-choice tests revealed that mealybug-infested plants were preferred to mealybugs alone and mealybug-damaged plants and were the major sources of volatiles that attract females coccinellids to the microhabitat of its prey. The emission of volatile chemicals did not appear to be limited to the infested parts of the plant but did occur systemically throughout the plant. The presence of conspecific coccinellid larvae or adult males did not modify the attractiveness of the mealybug-infested plants. However, when an infested plant with conspecific predator females (alone or with conspecific males) was compared to an infested plant or infested plant with conspecific males, E. flaviventris females showed a preference for the last two sources of odor. The uninfested plant with conspecific males was also preferred to the uninfested plant with conspecific females. In addition, the odor of conspecific males was preferred over that of conspecific females. Female predators preferred the plant infested with unparasitized mealybugs over the plant infested with mealybugs previously parasitized. These results showed that E. flaviventris females use herbivore-induced plant volatiles during foraging and can detect via olfaction the presence of conspecific gravid females and parasitized prey, thus assessing patch suitability from a distance.     

Digestion and Gastrointestinal Absorption of the 14–16-kDa Rice Allergens

The digestibility and gastrointestinal absorption of 14–16-kDa rice allergens (RAs) were investigated. RAs and bovine serum albumin (BSA) were first evaluated for their digestibility. BSA was digested completely by in vitro incubation with some proteases, but RAs remained almost intact. Administered orally (20 mg per mouse), intact RAs were clearly detected in the small intestine even 60 min after the administration, the amount of total RAs in the small intestine being estimated to be 0.59 mg. RAs were then biotinylated and infused into the duodenal lumen of anesthetized mice, and portal blood was collected. The RA concentrations in the portal plasma were respectively estimated to be 0.4–0.9 and 0.3–2.5 μg/ml for 0.4 and 4 mg doses. These results suggest that RAs are highly resistant to digestive enzymes and that about 1/100 of orally administered RAs remain intact in the small intestine, while at least 1/1,000–1/10,000 is absorbed and delivered into circulated blood.     

Investigations of Biodeterioration by Fungi in Historic Wooden Churches of Chiloé, Chile

The use of wood in construction has had a long history and Chile has a rich cultural heritage of using native woods for building churches and other important structures. In 2000, UNESCO designated a number of the historic churches of Chiloé, built entirely of native woods, as World Heritage Sites. These unique churches were built in the late 1700 s and throughout the 1800 s, and because of their age and exposure to the environment, they have been found to have serious deterioration problems. Efforts are underway to better understand these decay processes and to carryout conservation efforts for the long-term preservation of these important structures. This study characterized the types of degradation taking place and identified the wood decay fungi obtained from eight historic churches in Chiloé, seven of them designated as UNESCO World Heritage sites. Micromorphological observations identified white, brown and soft rot in the structural woods and isolations provided pure cultures of fungi that were identified by sequencing of the internal transcribed region of rDNA. Twenty-nine Basidiomycota and 18 Ascomycota were found. These diverse groups of fungi represent several genera and species not previously reported from Chile and demonstrates a varied microflora is causing decay in these historic buildings.     

Context Matters—Using an Agent-Based Model to Investigate the Influence of Market Context on the Supply of Local Biomass for Anaerobic Digestion

Biogas plant managers often face difficulties in obtaining feedstock at stable and affordable prices. The context in which the biogas plant manager needs to purchase the feedstock could be important when the biomass is also used in valorization trajectories besides anaerobic digestion. Using a combination of qualitative research and agent-based modelling, we investigated the effect of market context on the purchase of local biomass for anaerobic digestion. This paper details the institutional arrangements of our case study, the silage maize market in Flanders and the results of a scenario analysis, simulating nine different market contexts. Silage maize is an interesting case study, as it is both used for feed by farmers and as an input in biogas plants. The results show that mainly the time of entry into the market explains the difficulties in obtaining a stable supply of silage maize to biogas plants. Furthermore, we found a silage maize price increase for farmers in competition with a biogas plant, especially in case of a silage maize deficit in the market. The different institutional arrangements used have no significant effect. Our findings may guide biogas plant managers in assessing and reducing the consequences of the establishment of a biogas plant, competing for local biomass resources.     

Invasibility of Nectarless Flowers in Plant–Pollinator Systems

This paper considers plant–pollinator systems in which plants are divided into two categories: The plants that secret a substantial volume of nectar in their flowers are called secretors, while those without secreting nectar are called nonsecretors (cheaters). The interaction between pollinators and secretors is mutualistic, while the interaction between pollinators and nonsecretors is parasitic. Both interactions can be described by Beddington–DeAngelis functional responses. Using dynamical systems theory, we show global dynamics of a pollinator–secretor–cheater model and demonstrate mechanisms by which nectarless flowers/nonsecretors can invade the pollinator–secretor system and by which the three species could coexist. We define a threshold in the nonsecretors’ efficiency in translating pollinator–cheater interaction into fitness, which is determined by parameters (factors) in the systems. When their efficiency is above the threshold, non-secretors can invade the pollinator–secretor system. While the nonsecretors’ invasion often leads to their persistence in pollinator–secretor systems, the model demonstrates situations in which the non-secretors’ invasion can drive secretors into extinction, which consequently leads to extinction of the nonsecretors themselves.     

Plant–bacteria interactions in the removal of pollutants

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Highlights► Rhizobacteria degrade a wide range of pollutants and efficiently colonize plant roots. ► Plants have an effect on the selection of their own rhizospheric microorganisms. ► Catabolic pathways can be induced by natural secondary plant products. ► Horizontal gene transfer has an important role in bioremediation. ► Manipulation of plant/microbe interactions could improve rhizoremediation outcomes.