Co-evolution of fungal pathogens with teosinte to maize

Agricultural epidemics occur when novel strains of fungi appear that are virulent on monocultures of plants. We usually have no idea of how these strains arise or where they come from. Hypotheses of mutation, recombination, or horizontal gene transfer of a virulence factor are proposed to explain the former question. The latter question is usually addressed by invoking host jumps from surrounding plants (e.g. weeds) that may be closely or distantly related, or by long-distance dispersal from distant populations. As a model system, I plan to investigate the fungi that occur on wild population of teosinte in Mexico, where this progenitor of maize is endemic, and compare these fungi to those that are found on descendent cultivated populations of maize. Two speices of Fusarium that are significant pathogens of maize have already been found on teosinte. These and other fungi may serve as models for the co-evolution of fungus and host, in terms of pathogenicity and virulence factors, which may include secondary metabolites, and in terms of their population genetics, which may feature broader genetic diversity in the fungi in wild populations cf. agricultural populations and thus exist as reservoirs for novel virulent strains.

Evolution of pathogenicity factors and conditionally dispensable chromosomes in the plant pathogen Nectria haematococca

This pathogen of pea contains an enzyme (pisatin demethylase) that detoxifies the phytoalexin (pisatin), which is produced to deter fungal infections. Only strains of this fungus that have this ability can colonize pea and cause significant disease. This gene resides on a small chromosome that can be lost, with the only evident phenotypic change being the loss of the ability to be a pathogen of pea. We are investigating the origin of pisatin demethylase, which is a P450 cytochrome, and thus a member of a huge gene superfamily. A gene genealogical approach will indicate when this P450 diverged and evolved the ability to detoxify pisatin, and whether the known orthologs of this gene found in polyphyletic pathogens of pea were inherited vertically from a common ancestor, or gained by horizontal gene transfer in a common infection court. We are also investigating the structure and inferring the origin of the conditionally dispensable chromosome, which is part of the larger project to sequence the genome of this fungus. This project is a collaboration with Hans Van Etten.

Population genetics of Coccidioides posadasii, cause of Valley Fever in Arizona

Valley Fever is the most common nonsexally transmitted disease in Arizona. We are investigating the fungus that causes this disease, in order to determine if this species is structured by geography (is gene flow limited within Arizona?) by site (is clonality important? do rodents play a role in the patchy distribution of Coccidioides in soil?), by host (are humans, dogs, rodents and other species all susceptible to the same strains?). This information will be useful to understanding the epidemiology and pathology of this disease, and may help design strategies to reduce the incidence of this disease. This project is a collaboration with John Galgiani (VA) and Marc Orbach. This product will be the basis of graduate student Bridget Barker’s Ph.D. dissertation.

Comparative proteomics of euascomcyete fungi in response to their symbiotic hosts (Bio5 initiative)

We are looking for secreted factors in common to euascomycete fungi that interact with a range of host organisms, in order to understand how these fungi evolved so many different trophic interactions from an ancestral genome. The ultimate goal is making use of these common features as targets against pathogenic fungi.

Mandel MA Galgiani JN Kroken S Orbach MJ. Nov 2006. Coccidioides posadasii contains single chitin synthase genes corresponding to classes I to VII. Fungal Genet Biol, 43:775-88

Baker SE, Kroken S, Inderbitzin P, Asvarak T, Li BY, Shi L, Yoder OC, Turgeon BG. Feb 2006. Two polyketide synthase-encoding genes are required for biosynthesis of the polyketide virulence factor, T-toxin, by Cochliobolus heterostrophus. Mol Plant Microbe Interact, 19:139-49

Lee BN, Kroken S, Chou DY, Robbertse B, Yoder OC, Turgeon BG. Mar 2005. Functional analysis of all nonribosomal peptide synthetases in Cochliobolus heterostrophus reveals a factor, NPS6, involved in virulence and resistance to oxidative stress. Eukaryot Cell, 4:545-55

Kroken S, Glass NL, Taylor JW, Yoder OC, Turgeon BG. Dec 2003. Phylogenomic analysis of type I polyketide synthase genes in pathogenic and saprobic ascomycetes.. Proc Natl Acad Sci U S A, 100(26):15670-15675

Lu SW, Kroken S, Lee BN, Robbertse B, Churchill AC, Yoder OC, Turgeon BG. May 2003. A novel class of gene controlling virulence in plant pathogenic ascomycete fungi.. Proc Natl Acad Sci U S A, 100(10):5980-5985

Galagan JE et al. Apr 2003. The genome sequence of the filamentous fungus Neurospora crassa.. Nature, 422(6934):859-868

Paszkowski U, Kroken S, Roux C, Briggs SP. Oct 2002. Rice phosphate transporters include an evolutionarily divergent gene specifically activated in arbuscular mycorrhizal symbiosis.. Proc Natl Acad Sci U S A, 99(20):13324-13329

Hogberg N, Kroken S, Thor G, Taylor JW. Jul 2002. Reproductive mode and genetic variation suggest a North American origin of European Letharia vulpina.. Mol Ecol, 11(7):1191-1196

Displaying 1 - 8 of 14     << first < prev | [1] | 2 | next > last >>