RESUMO
Immune priming in invertebrates occurs when the first contact with a pathogen/parasite enhances resistance after a second encounter with the same strain or species. Although the mechanisms are not well understood, there is evidence that priming the immune response of some hosts leads to greater pro-oxidant production. Parasites, in turn, might counteract the host attack with antioxidants. Virulent pathogen strains may therefore mask invertebrate immune priming. For example, different parasite species overexpress catalase as a virulence factor to resist host pro-oxidants, possibly impairing the immune priming response. The aim of this study was firstly to evaluate the specificity of immune priming in Tenebrio molitor when facing homologous and heterologous challenges. Secondly, homologous challenges were carried out with two Metarhizium anisopliae strains (Ma10 and CAT). The more virulent strain (CAT) overexpresses catalase, an antioxidant that perhaps impairs a host immune response mediated by reactive oxygen species (ROS). Indeed, T. molitor larvae exhibited better immune priming (survival) in response to the Ma10 than CAT homologous challenge. Moreover, the administration of paraquat, an ROS-promoting agent, favoured survival of the host upon exposure to each fungal strain. We propose that some pathogens likely overcome pro-oxidant-mediated immune priming defences by producing antioxidants such as catalase.
Assuntos
Antioxidantes/metabolismo , Catalase/metabolismo , Evasão da Resposta Imune , Fatores Imunológicos/metabolismo , Metarhizium/enzimologia , Metarhizium/imunologia , Tenebrio/imunologia , Animais , Análise de SobrevidaRESUMO
Immune priming in invertebrates refers to an improved immune response (and therefore a better chance of survival) upon a second encounter with a specific pathogen. Although the existence of immune priming has been evaluated in invertebrate hosts, the ability of a particular entomopathogen species or strain to influence the occurrence of immune priming has not been thoroughly evaluated. The aim of the current study was to compare the occurrence of immune priming in Tenebrio molitor larvae after homologous challenges (a dual exposure to similar entomopathogens) with Serratia marcescens, Bacillus thuringiensis and Metarhizium anisopliae. Larvae presented more effective immune priming (measured as survival rates) when exposed to M. anisopliae or B. thuringiensis than when exposed to S. marcescens. We hypothesize that the toll pathway may help T. molitor survive these enemies and that the IMD pathway may be expressed to a lesser degree in this species, which may explain why they succumb to Gram-negative bacteria. This and other recent evidence suggest that the occurrence of immune priming in these organisms must not be ruled out until this phenomenon is tested with different entomopathogens.
Assuntos
Interações Hospedeiro-Patógeno/imunologia , Imunidade Inata , Larva/imunologia , Tenebrio/imunologia , Animais , Bacillus thuringiensis/patogenicidade , Larva/microbiologia , Metarhizium/patogenicidade , Serratia marcescens/patogenicidade , Especificidade da Espécie , Análise de Sobrevida , Tenebrio/microbiologiaRESUMO
The dimorphic yeast Yarrowia lipolytica is used as a model to study fungal differentiation because it grows as yeast-like cells or forms hyphal cells in response to changes in environmental conditions. Here, we report the isolation and characterization of a gene, ZNC1, involved in the dimorphic transition in Y. lipolytica. The ZNC1 gene encodes a 782 amino acid protein that contains a Zn(II)2C6 fungal-type zinc finger DNA-binding domain and a leucine zipper domain. ZNC1 transcription is elevated during yeast growth and decreases during the formation of mycelium. Cells in which ZNC1 has been deleted show increased hyphal cell formation. Znc1p-GFP localizes to the nucleus, but mutations within the leucine zipper domain of Znc1p, and to a lesser extent within the Zn(II)2C6 domain, result in a mislocalization of Znc1p to the cytoplasm. Microarrays comparing gene expression between znc1::URA3 and wild-type cells during both exponential growth and the induction of the yeast-to-hypha transition revealed 1,214 genes whose expression was changed by 2-fold or more under at least one of the conditions analyzed. Our results suggest that Znc1p acts as a transcription factor repressing hyphal cell formation and functions as part of a complex network regulating mycelial growth in Y. lipolytica.
Assuntos
Proteínas Fúngicas/metabolismo , Hifas/crescimento & desenvolvimento , Hifas/metabolismo , Fatores de Transcrição/metabolismo , Yarrowia/crescimento & desenvolvimento , Yarrowia/metabolismo , Leveduras/crescimento & desenvolvimento , Leveduras/metabolismo , Proteínas Fúngicas/genética , Hifas/genética , Fatores de Transcrição/genética , Yarrowia/genética , Leveduras/genéticaRESUMO
The gene ODC1, which codes for the ornithine decarboxylase enzyme, was isolated from the entomopathogenic fungus, Metarhizium anisopliae. The deduced amino acid sequence predicted a protein of 447 amino acids with a molecular weight of 49.3 kDa that contained the canonical motifs of ornithine decarboxylases. The ODC1 cDNA sequence was expressed in Escherichia coli cells; radiometric enzyme assays showed that the purified recombinant protein had ornithine decarboxylase activity. The optimum pH of the purified Odc1 protein was 8.0-8.5, and the optimum reaction temperature was 37°C. The apparent K(m) for ornithine at a pyridoxal phosphate concentration of 20mM was 22 µM. The competitive inhibitor of ODC activity, 1,4-diamino-2-butanone (DAB), at 0.25 mM inhibited 95% of ODC activity. The ODC1 mRNA showed an increase at the beginning of appressorium formation in vitro. During the M. anisopliae invasion process into Plutella xylostella larvae, the ODC1 mRNA showed a discrete increase within the germinating spore and during appressorium formation. The second expression peak was higher and prolonged during the invasion and death of the insect. The ODC1 gene complements the polyamine auxotrophy of Yarrowia lipolytica odc null mutant.