The Moss Physcomitrella patens as a Model System to Study Interactions between Plants and Phytopathogenic Fungi and Oomycetes

The moss Physcomitrella patens has a great potential as a model system to perform functional studies of plant interacting with microbial pathogens. P. patens is susceptible to fungal and oomycete infection, which colonize and multiply in plant tissues generating disease symptoms. In response to infection, P. patens activates defense mechanisms similar to those induced in flowering plants, including the accumulation of reactive oxygen species, cell death with hallmarks of programmed cell death, cell wall fortification, and induction of defense-related genes like PAL, LOX, CHS, and PR-1. Functional analysis of genes with possible roles in defense can be performed due to the high rate of homologous recombination present in this plant that enables targeted gene disruption. This paper reviews the current knowledge of defense responses activated in P. patens after pathogen assault and analyzes the advantages of using this plant to gain further insight into plant defense strategies

Adaptation Mechanisms in the Evolution of Moss Defenses to Microbes

The tri-colored bat (Perimyotis subflavus) has declined severely across its range since 2006 due to white nose syndrome, a fungal disease causing massive bat mortality in North America. My objective was to determine distinguishing characteristics of roost trees and habitat used by tri-colored bats so that the species’ needs can be considered in management plans. I mist-netted for tri-colored bats in western Kentucky and Tennessee during the summers of 2015 and 2016, and attached a radio transmitter to each captured adult bat. I tracked 15 bats to their day roosts and collected habitat data at 38 roost areas and at 74 randomly selected trees in the area of the capture radius of each bat for comparison. Tri-colored bats used roost trees within a relatively small area. The average distance between roosts was 86 m and bats roosted within 2.5 km of their original capture site. All roosting bats were located in the foliage of live trees. Tri-colored bats’ roost tree selection was nonrandom. Bats were observed roosting in nine different species of tree, with the most commonly selected species being Carya tomentosa and Quercus alba (46% and 23% of roost trees, respectively). The most abundant species among the randomly selected trees was Q. alba, which was selected roughly in proportion to its abundance, and Acer saccharum, which was never selected as a roost tree species. A generalized linear model on all variables measured showed that increasing tree crown depth, distance from roads, and basal area of trees were correlated with roost tree selection. Management needs of tri-colored bats differ from those of several other declining bat species which prefer trees in mid-decay stages. Tri-colored bats in my study typically used mature live deciduous trees that were further than average from roads, had a greater than average crown depth, and were in a location with higher than average basal area of trees. It is likely necessary to conserve large parcels of heterogenous forest, with high numbers of mature trees to adequately protect habitat for remnant populations of tri-colored bat that persist on the landscape

Oxylipins in moss development and defense

Oxylipins are oxygenated fatty acids that participate in plant development and defense against pathogen infection, insects and wounding. Initial oxygenation of substrate fatty acids is mainly catalyzed by lipoxygenases and alpha-dioxygenases but can also take place non-enzymatically by autoxidation or singlet oxygen-dependent reactions. The resulting hydroperoxides are further metabolized by secondary enzymes to produce a large variety of compounds, including the hormone jasmonic acid and short-chain green leaf volatiles. In flowering plants, which lack arachidonic acid, oxylipins are produced mainly from oxidation of polyunsaturated C18 fatty acids, notably linolenic and linoleic acids. Algae and mosses in addition possess polyunsaturated C20 fatty acids including arachidonic and eicosapentaenoic acids, which can also be oxidized by lipoxygenases and transformed into bioactive compounds. Mosses are phylogenetically placed between unicellular green algae and flowering plants, allowing evolutionary studies of the different oxylipin pathways. During the last years the moss Physcomitrella patens has become an attractive model plant for understanding oxylipin biosynthesis and diversity. In addition to the advantageous evolutionary position, functional studies of the different oxylipin-forming enzymes can be performed in this moss by targeted gene disruption or single point mutations by means of homologous recombination. Biochemical characterization of several oxylipin-producing enzymes and oxylipin profiling in P. patens reveal the presence of a wider range of oxylipins compared to flowering plants, including C18 as well as C20-derived oxylipins. Surprisingly, one of the most active oxylipins in plants, jasmonic acid, is not synthesized in this moss. In this review we present an overview of oxylipins produced in mosses and discuss the current knowledge related to the involvement of oxylipin-producing enzymes and their products in moss development and defense

Soybean stem canker caused by diaporthe caulivora; pathogen diversity, colonization process, and plant defense activation

Soybean is an important crop in South America, and its production is limited by fungal diseases caused by species from the genus Diaporthe, including seed decay, pod and stem blight, and soybean stem canker (SSC). In this study, we focused on Diaporthe species isolated from soybean plants with SSC lesions in different parts of Uruguay. Diaporthe diversity was determined by sequencing the internal transcribed spacer (ITS) regions of ribosomal RNA and a partial region of the translation elongation factor 1-alpha gene (TEF1α). Phylogenetic analysis showed that the isolates belong to five defined groups of Diaporthe species, Diaporthe caulivora and Diaporthe longicolla being the most predominant species present in stem canker lesions. Due to the importance of D. caulivora as the causal agent of SSC in the region and other parts of the world, we further characterized the interaction of this pathogen with soybean. Based on genetic diversity of D. caulivora isolates evaluated with inter-sequence single repetition (ISSR), three different isolates were selected for pathogenicity assays. Differences in virulence were observed among the selected D. caulivora isolates on susceptible soybean plants. Further inspection of the infection and colonization process showed that D. caulivora hyphae are associated with trichomes in petioles, leaves, and stems, acting probably as physical adhesion sites of the hyphae. D. caulivora colonized the stem rapidly reaching the phloem and the xylem at 72 h post-inoculation (hpi), and after 96 hpi, the stem was heavily colonized. Infected soybean plants induce reinforcement of the cell walls, evidenced by incorporation of phenolic compounds. In addition, several defense genes were induced in D. caulivora–inoculated stems, including those encoding a pathogenesis-related protein-1 (PR-1), a PR-10, a β-1,3-glucanase, two chitinases, two lipoxygenases, a basic peroxidase, a defensin, a phenylalanine-ammonia lyase, and a chalcone synthase. This study provides new insights into the interaction of soybean with D. caulivora, an important pathogen causing SSC, and provides information on the activation of plant defense responses

The Physcomitrella patens unique alpha-dioxygenase participates in both developmental processes and defense responses

[Background] Plant α-dioxygenases catalyze the incorporation of molecular oxygen into polyunsaturated fatty acids leading to the formation of oxylipins. In flowering plants, two main groups of α-DOXs have been described. While the α-DOX1 isoforms are mainly involved in defense responses against microbial infection and herbivores, the α-DOX2 isoforms are mostly related to development. To gain insight into the roles played by these enzymes during land plant evolution, we performed biochemical, genetic and molecular analyses to examine the function of the single copy moss Physcomitrella patens α-DOX (Ppα-DOX) in development and defense against pathogens.[Results] Recombinant Ppα-DOX protein catalyzed the conversion of fatty acids into 2-hydroperoxy derivatives with a substrate preference for α-linolenic, linoleic and palmitic acids. Ppα-DOX is expressed during development in tips of young protonemal filaments with maximum expression levels in mitotically active undifferentiated apical cells. In leafy gametophores, Ppα-DOX is expressed in auxin producing tissues, including rhizoid and axillary hairs. Ppα-DOX transcript levels and Ppα-DOX activity increased in moss tissues infected with Botrytis cinerea or treated with Pectobacterium carotovorum elicitors. In B. cinerea infected leaves, Ppα-DOX-GUS proteins accumulated in cells surrounding infected cells, suggesting a protective mechanism. Targeted disruption of Ppα-DOX did not cause a visible developmental alteration and did not compromise the defense response. However, overexpressing Ppα-DOX, or incubating wild-type tissues with Ppα-DOX-derived oxylipins, principally the aldehyde heptadecatrienal, resulted in smaller moss colonies with less protonemal tissues, due to a reduction of caulonemal filament growth and a reduction of chloronemal cell size compared with normal tissues. In addition, Ppα-DOX overexpression and treatments with Ppα-DOX-derived oxylipins reduced cellular damage caused by elicitors of P. carotovorum.[Conclusions] Our study shows that the unique α-DOX of the primitive land plant P. patens, although apparently not crucial, participates both in development and in the defense response against pathogens, suggesting that α-DOXs from flowering plants could have originated by duplication and successive functional diversification after the divergence from bryophytes.This work was supported by Agencia Nacional de Investigación e Innovación (ANII) [grants FCE2007_376, FCE2011_6095, fellowships BE_POS_2009_726 (A. Castro) and BE_POS_2010_2533 (L. Machado)], UdelaR Uruguay/CSIC Spain (Joint project), the Swedish Research Council, and Programa de Desarrollo de las Ciencias Básicas (PEDECIBA) Uruguay. The Ppα-DOX cDNA was obtained from the RIKEN Biological Research Center, Tsukuba, Japan

Adaptation mechanisms in the evolution of moss defenses to microbes

Bryophytes, including mosses, liverworts and hornworts are early land plants that have evolved key adaptation echanisms to cope with abiotic stresses and microorganisms. Microbial symbioses facilitated plant colonization of land by enhancing nutrient uptake leading to improved plant growth and fitness. In addition, early land plants acquired novel defense mechanisms to protect plant tissues from pre-existing microbial pathogens. Due to its volutionary stage linking unicellular green algae to vascular plants, the non-vascular moss Physcomitrella patens is an interesting organism to explore the adaptation mechanisms developed in the evolution of plant defenses to microbes. Cellular and biochemical approaches, gene expression profiles, and functional analysis of genes by targeted gene disruption have revealed that several defense mechanisms against microbial pathogens are conserved between mosses and flowering plants. P. patens perceives pathogen associated molecular patterns by plasma membrane receptor(s) and transduces the signal through a MAP kinase (MAPK) cascade leading to the activation of cell wall associated defenses and expression of genes that encode proteins with different roles in plant resistance. After pathogen assault, P. patens also activates the production of ROS, induces a HR-like reaction and increases levels of some hormones. Furthermore, alternative metabolic pathways are present in P. patens leading to the production of a distinct metabolic scenario than flowering plants that could contribute to defense. P. patens has acquired genes by horizontal transfer from prokaryotes and fungi, and some of them could represent adaptive benefits for resistance to biotic stress. In this review, the current knowledge related to the evolution of plant defense responses against pathogens will be discussed, ocusing on the latest advances made in the model plant P. patens

The moss-specific transcription factor PpERF24 positively modulates immunity against fungal pathogens in Physcomitrium patens

APETALA2/ethylene response factors (AP2/ERFs) transcription factors (TFs) have greatly expanded in land plants compared to algae. In angiosperms, AP2/ERFs play important regulatory functions in plant defenses against pathogens and abiotic stress by controlling the expression of target genes. In the moss Physcomitrium patens, a high number of members of the ERF family are induced during pathogen infection, suggesting that they are important regulators in bryophyte immunity. In the current study, we analyzed a P. patens pathogen-inducible ERF family member designated as PpERF24. Orthologs of PpERF24 were only found in other mosses, while they were absent in the bryophytes Marchantia polymorpha and Anthoceros agrestis, the vascular plant Selaginella moellendorffii, and angiosperms. We show that PpERF24 belongs to a moss-specific clade with distinctive amino acids features in the AP2 domain that binds to the DNA. Interestingly, all P. patens members of the PpERF24 subclade are induced by fungal pathogens. The function of PpERF24 during plant immunity was assessed by an overexpression approach and transcriptomic analysis. Overexpressing lines showed increased defenses to infection by the fungal pathogens Botrytis cinerea and Colletotrichum gloeosporioides evidenced by reduced cellular damage and fungal biomass compared to wild-type plants. Transcriptomic and RT-qPCR analysis revealed that PpERF24 positively regulates the expression levels of defense genes involved in transcriptional regulation, phenylpropanoid and jasmonate pathways, oxidative burst and pathogenesis-related (PR) genes. These findings give novel insights into potential mechanism by which PpERF24 increases plant defenses against several pathogens by regulating important players in plant immunity

Juventud, sectores populares y TIC en la Argentina

El artículo problematiza diferentes conceptos usualmente utilizados en el abordaje del vínculo entre Tecnologías de Información y Comunicación (TIC) y los sectores populares a partir de una investigación dedicada al estudio de la experiencia juvenil con la computadora e Internet en diferentes espacios de acceso público a las TIC situados en contextos de pobreza urbana en Argentina. Se recuperan nociones como la de brecha digital, pobreza digital y apropiación, al tiempo en que se indagan las estrategias que los sectores populares desarrollan para suplir las deficiencias sufridas en términos de acceso a equipamiento, conexión y competencias, y se reconstruyen las prácticas y significados otorgados a las TIC en la vida cotidiana de las y los jóvenes. A partir de los resultados del trabajo de campo de esta investigación y del análisis conceptual se alerta sobre la extrapolación acrítica de la difundida metáfora de “nativos digitales” a estas complejas realidades locales.Based on a research dedicated to assess the impact of public access to computers and Internet on urban poor youth in Argentina, this paper discusses those concepts that are commonly used in Poverty and ICT studies. Notions such as Digital Divide, Digital Poverty and Appropriation are analyzed as well as the strategies used by these groups to with ICT to compensate for their lack of access to equipment, connectivity and competencies. Youth practices and meanings attached to these technologies in their daily life are recovered in the work. Following this theoretical analysis and with the fieldwork results of the research the work addresses the problems surrounding a-critical extrapolations of the “digital natives” metaphor in such complex local realities.Fil: Benitez Larghi, Hector Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Aguerre Regusci, Carolina Inés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de San Andrés; ArgentinaFil: Calamari, Marina Laura. Universidad de San Andrés; ArgentinaFil: Fontecoba, Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Moguillansky, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín; ArgentinaFil: Ponce de León, Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; Argentin

Juventud, sectores populares y TIC en la Argentina

El artículo problematiza diferentes conceptos usualmente utilizados en el abordaje del vínculo entre Tecnologías de Información y Comunicación (TIC) y los sectores populares a partir de una investigación dedicada al estudio de la experiencia juvenil con la computadora e Internet en diferentes espacios de acceso público a las TIC situados en contextos de pobreza urbana en Argentina. Se recuperan nociones como la de brecha digital, pobreza digital y apropiación, al tiempo en que se indagan las estrategias que los sectores populares desarrollan para suplir las deficiencias sufridas en términos de acceso a equipamiento, conexión y competencias, y se reconstruyen las prácticas y significados otorgados a las TIC en la vida cotidiana de las y los jóvenes. A partir de los resultados del trabajo de campo de esta investigación y del análisis conceptual se alerta sobre la extrapolación acrítica de la difundida metáfora de “nativos digitales” a estas complejas realidades locales.Based on a research dedicated to assess the impact of public access to computers and Internet on urban poor youth in Argentina, this paper discusses those concepts that are commonly used in Poverty and ICT studies. Notions such as Digital Divide, Digital Poverty and Appropriation are analyzed as well as the strategies used by these groups to with ICT to compensate for their lack of access to equipment, connectivity and competencies. Youth practices and meanings attached to these technologies in their daily life are recovered in the work. Following this theoretical analysis and with the fieldwork results of the research the work addresses the problems surrounding a-critical extrapolations of the “digital natives” metaphor in such complex local realities.Fil: Benitez Larghi, Hector Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Aguerre Regusci, Carolina Inés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de San Andrés; ArgentinaFil: Calamari, Marina Laura. Universidad de San Andrés; ArgentinaFil: Fontecoba, Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Moguillansky, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín; ArgentinaFil: Ponce de León, Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; Argentin