title: Functional analysis of Ras in Colletotrichum trifolii.
abstract: Ras is a small monomeric GTP binding protein that transduces signals for growth and differentiation of eukaryotic organisms. Previously, a unique ras gene, designated Ct-ras, was cloned from the alfalfa fungal phytopathogen, Colletotrichum trifolii. Expression of Ct-Ras in mouse fibroblast cells (NIH3T3) demonstrated that Ct-ras is functionally similar to the mammalian ras genes since activating mutations of Ct-ras caused oncogenic phenotypes in nu/nu mice, including tumors. In C. trifolii, activated 'oncogenic' Ras (Val2) induced abnormal hyphal proliferation, defects in polarized growth and significantly reduced differentiation such as conidiation and appressorium formation in a nutrient dependent manner. Gene disruption of ct-ras was lethal. To further evaluate the function of Ct-Ras in C. trifolii, three different approaches were used: overexpression of cytosolic Ras by CAAX box deletion; expression of dominant negative Ct-RasT22N; and antisense ct-ras expression. Results showed that suppression of Ct-Ras activity significantly decreases fungal germination frequencies and hyphal growth rates. Taken together, these data suggest involvement of Ct-Ras in regulation of fungal cell growth and differentiation.
authors.affiliation: Department of Plant Pathology, University of Nebraska, 406G Plant Science Hall, Lincoln, NE 68583-0722, USA.
authors.forename: Young-sil
authors.initials: YS
authors.lastname: Ha
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Memmott
authors.forename: Martin B
authors.initials: MB
authors.lastname: Dickman
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors; D002867:Chromones / Q000494:pharmacology; D020231:Colletotrichum / Q000166:cytology / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D051231:Farnesyltranstransferase; D005656:Fungal Proteins; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020043:Genes, Essential; D005800:Genes, Fungal; D025301:Hyphae / Q000254:growth & development; D016254:Mutagenesis, Insertional; D020125:Mutation, Missense; D010082:Oxepins / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D016372:RNA, Antisense / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D015398:Signal Transduction / Q000235:genetics; D014158:Transcription, Genetic; D018631:ras Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D002867:Chromones; D005656:Fungal Proteins; D010082:Oxepins; D016372:RNA, Antisense; C452821:fusidienol; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; D019204:GTP-Binding Proteins; D018631:ras Proteins