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Molecular biological studies of Colletotrichum trifolii: Host interactions and regulatory GTP-binding proteins
Abstract
Colletotrictum trifolii is a filamentous fungal pathogen of alfalfa which causes a disease called anthracnose. The goals of this research were to investigate alfalfa-C. trifolii interactions during disease establishment, and signal transduction pathways regulating C. trifolii growth and development, by cloning and characterizing genes involved in these processes. mRNA differential display was used to identify genes induced in either alfalfa or C. trifolii during disease establishment. This approach was based on the hypothesis that plant and fungal genes important for disease will be induced when the plant and fungus interact, without assumptions concerning specific gene functions. A novel alfalfa gene, SRG1, was identified which was induced in response to plant stress. The amino acid sequence of the deduced Srg1 polypeptide was similar to a class of plant defense-related proteins. Growth and development of C. trifolii were investigated by making assumptions concerning specific gene functions in eukaryotes. In mammals and yeasts, heterotrimeric G proteins and the small G protein Ras transduce signals for cellular processes including growth and differentiation. Two C. trifolii genes, one encoding a homolog of the $\rm G\alpha$ subunit of heterotrimeric G proteins, and the other encoding a Ras homolog were isolated. The $\rm G\alpha$ gene (ctg-1) was partially characterized and found to be induced in germinating C. trifolii conidia, suggesting Ctg-1 plays a regulatory role during germination. The ras gene (CT-ras) was characterized by expressing mutationally activated forms of the gene in a mammalian system and in C. trifolii. Activated CT-ras induced transformation of mouse NIH 3T3 fibroblasts and tumor development in nu/nu mice, demonstrating conservation of ras gene function between mammals and filamentous fungi. In C. trifolii, activated CT-ras induced hyphal growth as well as defects in polarized growth and differentiation (conidiation) in a nutrient-dependent manner, demonstrating proper regulation of CT-Ras is required for normal hyphal development in C. trifolii.
Subject Area
Plant pathology|Molecular biology
Recommended Citation
Truesdell, Gina Michelle, "Molecular biological studies of Colletotrichum trifolii: Host interactions and regulatory GTP-binding proteins" (1998). ETD collection for University of Nebraska-Lincoln. AAI9826103.
https://digitalcommons.unl.edu/dissertations/AAI9826103