RESUMO
Like pathogens, beneficial endophytic fungi secrete effector proteins to promote plant colonization, for example, through perturbation of host immunity. The genome of the root endophyte Serendipita indica encodes a novel family of highly similar, small alanine- and histidine-rich proteins, whose functions remain unknown. Members of this protein family carry an N-terminal signal peptide and a conserved C-terminal DELD motif. Here we report on the functional characterization of the plant-responsive DELD family protein Dld1 using a combination of structural, biochemical, biophysical and cytological analyses. The crystal structure of Dld1 shows an unusual, monomeric histidine zipper consisting of two antiparallel coiled-coil helices. Similar to other histidine-rich proteins, Dld1 displays varying affinity to different transition metal ions and undergoes metal ion- and pH-dependent unfolding. Transient expression of mCherry-tagged Dld1 in barley leaf and root tissue suggests that Dld1 localizes to the plant cell wall and accumulates at cell wall appositions during fungal penetration. Moreover, recombinant Dld1 enhances barley root colonization by S. indica, and inhibits H2 O2 -mediated radical polymerization of 3,3'-diaminobenzidine. Our data suggest that Dld1 has the potential to enhance micronutrient accessibility for the fungus and to interfere with oxidative stress and reactive oxygen species homeostasis to facilitate host colonization.
Assuntos
Histidina , Hordeum , Alanina , Basidiomycota , Fungos , Homeostase , Hordeum/genética , Estresse Oxidativo , Doenças das Plantas , Raízes de PlantasRESUMO
Extracellular adenosine 5'-triphosphate (eATP) is an essential signaling molecule that mediates different cellular processes through its interaction with membrane-associated receptor proteins in animals and plants. eATP regulates plant growth, development, and responses to biotic and abiotic stresses. Its accumulation in the apoplast induces ROS production and cytoplasmic calcium increase mediating a defense response to invading microbes. We show here that perception of extracellular nucleotides, such as eATP, is important in plant-fungus interactions and that during colonization by the beneficial root endophyte Serendipita indica eATP accumulates in the apoplast at early symbiotic stages. Using liquid chromatography-tandem mass spectrometry, and cytological and functional analysis, we show that S. indica secrets SiE5'NT, an enzymatically active ecto-5'-nucleotidase capable of hydrolyzing nucleotides in the apoplast. Arabidopsis thaliana lines producing extracellular SiE5'NT are significantly better colonized, have reduced eATP levels, and altered responses to biotic stresses, indicating that SiE5'NT functions as a compatibility factor. Our data suggest that extracellular bioactive nucleotides and their perception play an important role in fungus-root interactions and that fungal-derived enzymes can modify apoplastic metabolites to promote fungal accommodation.
Assuntos
Trifosfato de Adenosina/metabolismo , Basidiomycota/fisiologia , Nucleotídeos/metabolismo , Plantas/microbiologia , Difosfato de Adenosina , Monofosfato de Adenosina , Arabidopsis/metabolismo , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/metabolismo , Espaço Extracelular/metabolismo , Hordeum , Interações Hospedeiro-Patógeno , Hidrólise , Modelos Moleculares , Proteínas de Plantas/química , Raízes de Plantas/microbiologia , Conformação Proteica , Estresse FisiológicoRESUMO
ß-glucans are well-known modulators of the immune system in mammals but little is known about ß-glucan triggered immunity in planta. Here we show by isothermal titration calorimetry, circular dichroism spectroscopy and nuclear magnetic resonance spectroscopy that the FGB1 gene from the root endophyte Piriformospora indica encodes for a secreted fungal-specific ß-glucan-binding lectin with dual function. This lectin has the potential to both alter fungal cell wall composition and properties, and to efficiently suppress ß-glucan-triggered immunity in different plant hosts, such as Arabidopsis, barley and Nicotiana benthamiana. Our results hint at the existence of fungal effectors that deregulate innate sensing of ß-glucan in plants.
Assuntos
Basidiomycota/metabolismo , Parede Celular/metabolismo , Proteínas Fúngicas/metabolismo , Lectinas/metabolismo , beta-Glucanas/metabolismo , Arabidopsis/imunologia , Arabidopsis/microbiologia , Basidiomycota/fisiologia , Proteínas Fúngicas/imunologia , Hordeum/imunologia , Hordeum/microbiologia , Interações Hospedeiro-Patógeno/imunologia , Imunidade Inata/imunologia , Lectinas/imunologia , Doenças das Plantas/imunologia , Doenças das Plantas/microbiologia , Imunidade Vegetal/imunologia , Raízes de Plantas/imunologia , Raízes de Plantas/microbiologia , Ligação Proteica , Nicotiana/imunologia , Nicotiana/microbiologiaRESUMO
Beside a cardinal role in coordination of many developmental processes in the plant, the phytohormone auxin has been recognized as a regulator of plant defense. The molecular mechanisms involved are still largely unknown. Using a sensitive chemiluminescence assay, which measures the oxidation of luminol in the presence of H2O2 by horseradish peroxidase (HRP), we report here on the ability of exogenously added indole-3-acetic acid (IAA) to enhance the suppressive effect of the root endophyte Piriformospora indica on the chitin-elicited oxidative burst in barley roots. Thus, the potential of P. indica to produce free IAA during the early colonization phase in barley might provide the symbiont with a means to interfere with the microbe-associated molecular patterns (MAMP)-triggered immunity.