RESUMO
In the present manuscript, we describe the mechanisms involved in the yeast-to-hypha dimorphic transition of the plant pathogenic Basidiomycota fungus Ustilago maydis. During its life cycle, U. maydis presents two stages: one in the form of haploid saprophytic yeasts that divide by budding and the other that is the product of the mating of sexually compatible yeast cells (sporidia), in the form of mycelial dikaryons that invade the plant host. The occurrence of the involved dimorphic transition is controlled by the two mating loci a and b. In addition, the dimorphic event can be obtained in vitro by different stimuli: change in the pH of the growth medium, use of different carbon sources, and by nitrogen depletion. The presence of other factors and mechanisms may affect this phenomenon; among these, we may cite the PKA and MAPK signal transduction pathways, polyamines, and factors that affect the structure of the nucleosomes. Some of these factors and conditions may affect all these dimorphic events, or they may be specific for only one or more but not all the processes involved. The conclusion reached by these experiments is that U. maydis has constituted a useful model for the analysis of the mechanisms involved in cell differentiation of fungi in general.
Assuntos
Transdução de Sinais , Ustilago/citologia , Ustilago/fisiologia , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Metilação de DNA , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Histidina Quinase/metabolismo , Histona Acetiltransferases/metabolismo , Homeostase , Concentração de Íons de Hidrogênio , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Poliaminas/metabolismoRESUMO
Ustilago maydis (DC) Cda., a phytopathogenic Basidiomycota, is the causal agent of corn smut. During its life cycle U. maydis alternates between a yeast-like, haploid nonpathogenic stage, and a filamentous, dikaryotic pathogenic form that invades the plant and induces tumor formation. As all the members of the Subphylum Ustilaginomycotina, U. maydis is unable to form basidiocarps, instead it produces teliospores within the tumors that germinate forming a septate basidium (phragmobasidium). We have now established conditions allowing a completely different developmental program of U. maydis when grown on solid medium containing auxins in dual cultures with maize embryogenic calli. Under these conditions U. maydis forms large hemi-spheroidal structures with all the morphological and structural characteristics of gastroid-type basidiocarps. These basidiocarps are made of three distinct hyphal layers, the most internal of which (hymenium) contains non-septate basidia (holobasidia) from which four basidiospores develop. In basidiocarps meiosis and genetic recombination occur, and meiotic products (basidiospores) segregate in a Mendelian fashion. These results are evidence of sexual cycle completion of an Ustilaginomycotina in vitro, and the demonstration that, besides its quasi-obligate biotrophic pathogenic mode of life, U. maydis possesses the genetic program to form basidiocarps as occurs in saprophytic Basidiomycota species.
Assuntos
Carpóforos/crescimento & desenvolvimento , Doenças das Plantas/microbiologia , Reguladores de Crescimento de Plantas/farmacologia , Ustilago/crescimento & desenvolvimento , Zea mays/microbiologia , Citocininas/farmacologia , DNA Fúngico/genética , Diploide , Carpóforos/citologia , Carpóforos/genética , Giberelinas/farmacologia , Haploidia , Hifas/citologia , Hifas/efeitos dos fármacos , Hifas/genética , Hifas/crescimento & desenvolvimento , Ácidos Indolacéticos/farmacologia , Meiose , Metamorfose Biológica , Recombinação Genética , Esporos Fúngicos/citologia , Esporos Fúngicos/efeitos dos fármacos , Esporos Fúngicos/genética , Esporos Fúngicos/crescimento & desenvolvimento , Ustilago/citologia , Ustilago/efeitos dos fármacos , Ustilago/genética , Virulência , Leveduras/citologia , Leveduras/efeitos dos fármacos , Leveduras/genética , Leveduras/crescimento & desenvolvimento , Zea mays/citologia , Zea mays/embriologiaRESUMO
The effects of octyl gallate on Ustilago maydis yeast cells were analysed in relation to its capacity to oxidize compounds (pro-oxidant actions). All phenolic compounds tested inhibited the alternative oxidase (AOX). However, only octyl gallate induced a morphological change in yeast cells and collapsed the mitochondrial membrane potential. In contrast to octyl gallate, propyl gallate and nordihydroguaiaretic acid caused only a negligible cell change and the membrane potential was not affected. Our findings show that structurally related phenolic compounds do not necessarily exert similar actions on target cells. Preincubation of U. maydis cells with trolox inhibited the change to pseudohyphal growth produced by octyl gallate. These results suggest that in addition to the inhibitory action of octyl gallate on the AOX, this compound induces a switch from yeast to a mycelium, probably through the formation of lipid peroxides.
Assuntos
Ácido Gálico/análogos & derivados , Ustilago/citologia , Ustilago/crescimento & desenvolvimento , Proteínas Fúngicas/metabolismo , Ácido Gálico/metabolismo , Potencial da Membrana Mitocondrial , Proteínas Mitocondriais , Oxirredutases/metabolismo , Proteínas de Plantas , Galato de Propila/metabolismo , Ustilago/metabolismoRESUMO
Ustilago maydis is an edible parasitic basidiomycete, which specifically infects corn (Zea mays) and teocintle (Z. diploperennis). To characterise the interaction between the basidiomycete and its host organism, we tested the effect of plant lectins with well-known sugar specificity on the growth and germination of U. maydis spores. Lectins specific for N-acetyl-D-galactosamine, such as those from Dolichos biflorus and Phaseolus lunatus, and the wheatgerm agglutinin specific for N-acetyl-D-glucosamine inhibited spore germination, but were ineffective in modifying U. maydis cell growth. The galactose-specific lectin from the corn coleoptyle inhibited both germination and cell growth, while the lectin concanavalin A (mannose/glucose specific) activated spore germination and growth. Our results suggest that specific saccharide-containing receptors participate in regulating the growth and maturation of U. maydis spores.