RESUMO
The gene-for-gene model postulates that for every gene determining resistance in the host plant, there is a corresponding gene conditioning avirulence in the pathogen. On the basis of this relationship, products of resistance (R) genes and matching avirulence (Avr) genes are predicted to interact. Here, we report on binding studies between the R gene product Cf-9 of tomato and the Avr gene product AVR9 of the pathogenic fungus Cladosporium fulvum. Because a high-affinity binding site (HABS) for AVR9 is present in tomato lines, with or without the Cf-9 resistance gene, as well as in other solanaceous plants, the Cf-9 protein was produced in COS and insect cells in order to perform binding studies in the absence of the HABS. Binding studies with radio-labeled AVR9 were performed with Cf-9-producing COS and insect cells and with membrane preparations of such cells. Furthermore, the Cf-9 gene was introduced in tobacco, which is known to be able to produce a functional Cf-9 protein. Binding of AVR9 to Cf-9 protein produced in tobacco was studied employing surface plasmon resonance and surface-enhanced laser desorption and ionization. Specific binding between Cf-9 and AVR9 was not detected with any of the procedures. The implications of this observation are discussed.
Assuntos
Cladosporium/genética , Cladosporium/patogenicidade , Proteínas Fúngicas/genética , Genes Fúngicos , Genes de Plantas , Glicoproteínas de Membrana/genética , Proteínas de Plantas/genética , Solanum lycopersicum/genética , Solanum lycopersicum/microbiologia , Animais , Células COS , Linhagem Celular , Proteínas Fúngicas/metabolismo , Solanum lycopersicum/metabolismo , Glicoproteínas de Membrana/metabolismo , Modelos Genéticos , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Ligação Proteica , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Spodoptera , Ressonância de Plasmônio de Superfície , Nicotiana/genética , Nicotiana/metabolismo , Virulência/genéticaRESUMO
The characterization of the hydroxylamine oxidase from the heterotrophic nitrifier Paracoccus denitrificans GB17 indicates the enzyme to be entirely distinct from the hydroxylamine oxidase from the autotrophic nitrifier Nitrosomonas europaea. Hydroxylamine oxidase from P. denitrificans contains three to five non-haem, non-iron-sulphur iron atoms as prosthetic groups, predominantly co-ordinated by carboxylate ligands. The interaction of the enzyme with the electron-accepting proteins cytochrome C556 and pseudoazurin is mainly hydrophobic. The catalytic mechanism of hydroxylamine oxidase from P. denitrificans is different from the enzyme from N. europaea because the production of nitrite by the former requires molecular oxygen. Under anaerobic conditions the enzyme makes nitrous oxide as a sole product.