Associate Professor, Warnell School of Forestry and Natural Resources
Ph.D. (1990) University of Wisconsin, Madison

Phone: 706-542-1205
Email: covert@uga.edu

Research in the Covert Lab

Molecular genetics of fungal-plant interactions.

Lab Members

Awards

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Research Interests

The research in the Covert lab focuses on two different fungal diseases of pine, pitch canker and fusiform rust. In our study of these problems we are addressing three broad questions:

1. How do fungi cause plant disease symptoms?
2. How do asymptomatic endophytes and obligately biotrophic fungi grow within their host plants?
3. How do fungal pathogens and plant hosts influence each other's development?

Specific aspects of our work and two diseases we study are described below.

Pitch canker affects many species of pine and is characterized by the presence of resin-weeping cankers, branch die-back, and seedling death. It is caused by the fungus Fusarium circinatum (teleomorph: Gibberella circinata), which is an ascomycete that infects via wounds. Pitch canker is an economically significant disease in the southeastern United States and in South Africa.

It also severely affects the native populations of Monterey pine in California. Much of our early work on this disease focused on developing techniques to manipulate F. circinatum in the lab. Most notably we developed the ability to conduct sexual crosses in vitro, to identify isolates' mating types in a PCR assay, and to transform this species with Agrobacterium tumefaciens.

Currently we are using the A. tumefaciens transformation system to create tagged mutants in F. circinatum. We are screening them for their ability to cause disease on Monterey pine as well as for their ability to grow asymptomatically in plants. This approach should allow us to identify F. circinatum genes that are essential for pitch canker symptom development as well as for in planta growth.

Fusiform rust affects slash pine and loblolly pine, the two most important commercial species of pine in the southeastern United States. It is characterized by the formation of woody galls on the stems and branches of infected trees. Fusiform rust is caused by the fungus Cronartium quercuum f. sp. fusiforme.

This obligate basidiomycete has no free living form in nature and must grow in association with oak leaves as well as with pine wood in order to complete its lifecycle.

We have used both differential display and suppression subtraction hybridization to identify pine genes that are induced or suppressed in response to fusiform rust infection.We hypothesize that these differentially expressed genes play roles in wood growth, host defense or nutrient provision to the pathogen. Experiments with clone arrays and with the Arabidopsis orthologs for selected pine genes are being carried out to test these hypotheses about gene function. We are also using suppression subtraction hybridization to identify C. q. fusiforme genes that are involved in spore development and germination, developmental events that are influenced by host morphology and/or biochemistry.

Selected Publications

Covert, S. F., A. Briley, M. M. Wallace, and V.T. McKinney. (1999) Partial MAT-2 gene structure and the influence of temperature on mating success in Gibberella circinata. Fungal Genetics and Biology 28:43-54.

Enkerli, J., H. Reed, A. Briley, G. Bhatt, and S.F. Covert (2000) Physical map of a conditionally dispensable chromosome in Nectria haematococca MP VI and location of chromosome breakpoints. Genetics 155:1083-1094.

Wallace, M.M., and S.F. Covert (2000) A molecular mating type assay for Fusarium circinatum. Applied and Environmental Microbiology 66:5506-5508.

Covert, S.F., P. Kapoor, M.-H. Lee, A. Briley, C.J. Nairn (2001) Agrobacterium tumefaciens-mediated transformation of Fusarium circinatum. Mycological Research 105:259-264.

Kelkar, HS, J Griffith, ME Case, SF Covert, RD Hall, CH Keith, JS Oliver, MJ Orbach, MS Sachs, JR Wagner, MJ Weise, JK Wunderlich, and J Arnold (2001) The Neurospora crassa Genome: Cosmid libraries sorted by chromosome. Genetics 157: 979-990.

Tsuchiya D., A. Matsumoto, S. F. Covert, C. R. Bronson, and M. Taga (2002) Physical mapping of plasmid and cosmid clones in filamentous fungi by fiber-FISH. Fungal Genetics and Biology 37:29-38.

Shiflett A., J. Enkerli, and S.F. Covert (2002) Nht2, a copia LTR retrotransposon from a conditionally dispensable chromosome in Nectria haematococca. Current Genetics 41:99-106.

Warren, J.M., and S.F. Covert (2004) Differential expression of pine and Cronartium quercuum f. sp. fusiforme genes in fusiform rust galls. Applied and Environmental Microbiology 70:441-451.

Morse, A.M.; Nelson, C.D.; Covert, S.F.; Holliday, A.G.; Smith, K.E.; Davis, J.M. (in press) Pine Genes Regulated by the Necrotrophic Pathogen Fusarium circinatum. Theoretical and Applied Genetics.