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Serine proteases and metalloproteases associated with pathogenesis but not host specificity in the Entomophthoralean fungus Zoophthora radicans

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Abstract:

The protease activity of a Zoophthora radicans strain that was highly infective toward Pieris brassicae (cabbage butterfly) larvae was compared with that of isogenic strains that were adapted to Plutella xylostella (diamondback moth) larvae through serial passage. All strains produced three distinct serine proteases ranging in size from 25 to 37 kDa; however, the original strain from P. brassicae also produced large amounts of an approximately 46 kDa metalloprotease. Subsequently, a cDNA encoding a 43 kDa (mature enzyme) zinc-dependent metalloprotease, ZrMEP1, was isolated from the original fungal strain and most likely corresponds to the 46 kDa protease observed with in-gel assays. ZrMEP1 possessed characteristics of both the fungalysin and thermolysin metalloprotease families found in some pulmonary and dermal pathogens. This is the first report of this type of metalloprotease from an entomo pathogenic fungus. A cDNA encoding a trypsin-like serine protease, ZrSP1, was also identified and was most similar to a serine protease from the plant pathogen Verticillium dahliae. In artificial media, ZrMEP1 and ZrSP1 were found to be differentially responsive to gelatin and catabolite repression in the fungal strains adapted to P. brassicae and P. xylostella, but their expression patterns within infected larvae were the same. It appears that while these proteases likely play a role in the infection process, they may not be major host specificity determinants.Key words: Zoophthora radicans, metalloprotease, serine protease, pathogenesis, entomopathogen, host specificity.

L'activité protéase d'une souche de Zoophthora radicans qui était fortement infectieuse chez la larve de Pieris brassicae (papillon du chou) a été comparée à celles de souches isogènes qui ont été adaptées aux larves de Plutella xylostella (fausse-teigne des crucifères) par des passages en série. Toutes les souches ont produit trois protéases à sérine distinctes de tailles variant entre 25 à 37 kDa; toutefois, la souche d'origine provenant de P. brassicae produisait également de grandes quantités d'une métalloprotéase d'environ 46 kDa. Par la suite, un ADNc codant une métalloprotéase dépendante du zinc de 43 kDa (enzyme mature), ZrMEP1, fut isolé de la souche des champignons d'origine et correspond sans aucun doute à la protéase de 46 kDa observée dans des tests en gels. ZrMEP1 possède des caractéristiques des familles de métalloprotéases fungalysines et thermolysines retrouvée chez certains pathogènes pulmonaires et dermiques et il s'agit de la première mention de ce type de métalloprotéases chez un champignon entomopathogène. Un ADNc codant une protéase à sérine semblable à la trypsine, ZrSP1, fut également identifié et a démontré des similitudes avec une protéase à sérine du pathogène de plantes Verticillium dahliae. Dans des milieux artificiels, ZrMEP1 et ZrSP1 ont démontré une réponse différentielle à la gélatine et à la répression cataboliques de la souche adaptée à P. brassicae et P. xylostella mais leurs profils d'expression à l'intérieur de larves infectées étaient les mêmes. Il semble que bien que ces protéases jouent probablement un rôle dans le processus d'infection elles ne seraient pas des déterminants majeurs de la spécificité de l'hôte. Mots clés : Zoophthora radicans, métalloprotéases, protéases à sérine, pathogenèse, entomopathogènes, spécificité à l'hôte. [Traduit par la Rédaction]

Document Type: Research Article

Publication date: June 1, 2006

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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