Oklahoma State University

Dr. Stephen Marek, Associate Professor



B.S., University of Missouri-Columbia, 1990
M.S., University of Missouri-Columbia, 1994
Ph.D., University of California-Davis, 2001
stephen.marek@okstate.edu


Teaching:

PLP 3343/5343    Principles of Plant Pathology


Research: Functional Genomics of Plant Pathogenic Fungi


  • Agrobacterium-mediated T-DNA tagging of genes involved in virulence and morphogenesis of fungi infecting Medicago spp. Numerous mutants of M. truncatula are available

  • Phoma medicaginis causes leaf spot and spring black stem and reproduces asexually, forming conidia in pycnidia. A T-DNA-tagged library of over 1000 transformants has been generated and numerous interesting mutant phenotypes in morphogenesis have been observed. Green and red fluorescent transformants are being used to dissect the cellular interactions of the fungus with Medicago.

  • Leptosphaerulina trifolii causes Lepto leaf spot and reproduces sexually, forming ascospores and pseudothecia. This fungus is closely related to Phoma medicaginis and provides a valuable system for comparison.




  • Phymatotrichum Root Rot (cotton root rot or Texas root rot), a collaboration with the Noble Foundation (Ardmore, OK) and University of Oklahoma, (Norman, OK). This notorious fungus inhabits the alkaline calcareous soils of the southwestern US and northern Mexico. It has broad host range of over 2000 dicot hosts and severely affects cotton, alfalfa, and numerous fruit and nut trees. We are using Medicago spp. (especially M. truncatula) as model hosts to better understand the host-pathogen interaction of this economically important disease. The long term goal is to identify resistant germplasm in Medicago.

  • Phylogenetics, population genetics and development of diagnostic tools for the casual fungus, Phymatotrichopsis omnivora (synonym Phymatotrichum omnivorum). Isolates of P. omnivora have been collected throughout its natural range in the southwestern US and are being genotyped. We hope to better understand the population genetics of this fungus in order to possibly identify races and/or the presence of genetic recombination between genotypes. Species- and genotype-specific markers are being developed.

  • Genomic and EST sequencing of Phymatotrichopsis omnivora. Bruce Roe's Lab at the University of Oklahoma has been using a whole genome shotgun sequencing approach combining new pyrosequencing data with traditional Sanger sequencing. ESTs (cDNA libraries) and BAC library clones are also being sequenced to aid annotation and assembly. The P. omnivora sequence data can be searched using BLAST.

  • Molecular characterization of the host-pathogen interaction. The Medicago host plant-side of the interaction is under study in the labs of Rick Dixon, Joe Bouton, Kiran Mysore, Lloyd Sumner and Carolyn Young at the Noble Foundation. Areas under study include the screening of Medicago germplasm for resistance, microarray analysis of plant gene expression during infection by P. omnivora, and antifungal phytochemicals. The fungal-side of the interaction is under study in our lab at OSU. We are characterizing ESTs from fungus during host plant infection and key life stages such as sclerotia, mycelial strand and sporemat formation. We hope to genetically transform P. omnivora in order to functionally characterize candidate virulence genes.




    Assessing the efficacy of the silicon supplementation in the control of important fungal pathogens of greenhouse ornamental crops, a collaboration with Sophia Kamenidou and Dr. Todd Cavins in the Horticulture and Landscape Architecture (now at Sun Gro Horticulture). We are examining how silicon protects floricultural crop plants grown in soilless peat mixes from Botrytis blight (gray mold), powdery mildew and Phytophthora root rot.




    Molecular characterization of the rhizosphere fungi of tallgrass prairies and of the host-pathogen interaction of ectotrophic root fungi with turfgrasses are collaborations with Dr. Nathan Walker in Plant Pathology. In order to understand the impacts of indigenous soilborne fungi on native and introduced grasses, we are following the population dynamics of fungi inside the roots of grasses using molecular barcoding and metagenomic analyses. Most of the collections are being made from keystone grass species at the Nature Conservancy's Tallgrass Prairie Preserve, in order to best approximate a pristine rhizosphere, untouched by modern agriculture. To better understand spring dead spot of bermudagrass, the causal fungus Ophiosphaerella herpotricha has been transformed to express GFP and is being used to study its interaction with Cynodon spp.

    Laboratory Personnel and Graduate Students:


    Ian Moncrief, MS Student in Plant Pathology
    Research: Molecular karyotyping of Phymatotrichum omnivora isolates and following the expression of candidate virulence factors during infection of host plant roots.


    Sophia Kamenidou, PhD Student in Plant Science (Advisor: Dr. Mike Smith, HLA)
    Research: Silicon supplementation of greenhouse floricultural crops for disease suppression of Botrytis blight, powdery mildew and Phytophthora root rot. Agrotransformed Botrytis cinerea to express GFP and DsRed to study the cytology of silicon-induced resistance.


    Gayan Herath, pursuing MS in environmental engineering
    Jennifer Nguyen, pursuing BS in chemical engineering and BA in music
    Jillian Prather, pursuing BS in biochemistry and molecular biology


    Former Laboratory Personnel:


    Dr. Carrie Smith, Postdoctoral Fellow (2008-2009)
    Research: Construction and validation of Agrotransformation vectors and signature-tagged ESTs for Phymatotrichopsis omnivora. Characterization and identification of T-DNA tagged genes in Phoma medicaginis.


    Madhavi Dhulipala, MS Student in Plant Pathology
    Research: Foliar pathosystems for Medicago truncatula, T-DNA tagged (insertional mutagenesis using Agrobacterium-mediated transformation) library of Phoma medicaginis, characterization of the virulence and morphogenesis of generated mutants, cytology of the interaction of P. medicaginis and the closely related Leptosphaerulina trifolii with Medicago spp.
    Currently mentoring up-and-coming fungal geneticist, Revah Sambaraju.


    (James is one not wearing a hat)
    James N. Enis, Research Specialist (2003-2005)
    Research: construction binary vectors for Agrobacterium-mediated transformation of fungi, TAIL-PCR, amplification of phylogenetic genes from fungi, methodical record keeping.
    Currently: Teaching at Eastern Oklahoma State College and raising a family near Wilburton, OK.


    Sandrine Casanova, Technical Paraprofessional (2005-2006)
    Research: dogged transformation of recalcitrant fungi, amplification of Medicago truncatula mutants, phylogeographic study of Phymatotrichopsis omnivora.
    Currently: Pursuing a health management degree in France.


    Victor Hernandez-Gordillo (2006)
    Research: testing binary vectors for Agrobacterium-mediated transformation of fungi, cDNA libraries.
    Currently: pursuing a PhD at Purdue University.


    Jenny Stacey, INBRE intern (summer 2006)
    Research: characterization of melanization and virulence of insertional mutants of Phoma medicaginis.
    Currently: pursuing her BS in biology in Oklahoma City.


    Dr. Tim Samuels, Post Doctoral Fellow, 2006-2007 Research: Transcriptome characterization and protoplast transformation of Phymatotichopsis omnivora. Constructed numerous cDNA libraries of P. omnivora during various developmental and parasitic stages and initiated the construction of novel P. omnivora-specific transformation vectors.
    Currently: Working as a Senior Molecular Genetic Specialist in the Department of Plant and Soil Sciences at OSU.

    Hourly Technicians:

    Richard Muller, BS in Microbiology (with Walker Lab)
    Sibo Hlatywayo, BS student in Chemical Engineering
    Myla Mirdo, BS student in Microbiology (with Walker Lab)
    Cody Key, pre-Pharm-BS student in Microbiology

    Photo from lab party for Sandrine and Victor

    Recent Publications:

    Kamenidou S, Cavins TJ, Marek SM. 2008. Silicon supplements affect horticultural traits of greenhouse-produced ornamental sunflowers. HortScience 43: 236-239.

    Caasi, OC, Walker, NR, Marek, SM, Mitchell, TK. 2007. Infection and colonization of three turf-type bermudagrass cultivars by Ophiosphaerella herpotricha expressing green fluorescent protein. Phytopathology 97:S16

    Dhulipala, M, Marek, SM. 2007. Phoma medicaginis as a model pathosystem for Medicago. Phytopathology 97:S28.

    Dhulipala MR, Enis JN, Casanova S, Marek SM. 2006. Transformation of Leptosphaerulina trifolii and its interaction with Medicago. Phytopathology 96: S29.

    Kamenidou S, Casanova S, Dhulipala MR, Enis JN, Cavins TJ, Marek SM. 2006. Transformation of Botrytis cinerea with GFP - A tool to study the cytology of silicon-induced resistance against gray mold. Phytopathology 96: S57.

    Lee HK, Marek SM, Young C, Sledge M. 2006. Variation for Phymatotrichopsis omnivora alfalfa (Medicago sativa L.) Phytopathology 96: S65.

    Marek SM, Cavins TJ, Kamenidou S. 2006. Soluble silicon-based disease management of floricultural crops. Greenhouse Product News 16: 62.

    Marek SM, Muller RM, Walker NR. 2006. First report of ergot of bermudagrass caused by Claviceps cynodontis in Oklahoma. Plant Disease 90: 376.

    Walker, N. R., Mitchell, T. K., Morton, A. N., and Marek, S. M. 2006. Influence of temperature and time of year on colonization of bermudagrass roots by Ophiosphaerella herpotricha. Plant Dis. 90:1326-1330.

    Lee HK, Marek SM, Sledge MK. 2005. Growth chamber assay for Phymatotrichum root rot of Medicago species. Phytopathology 95: S1112.

    Lee HK, Marek SM, Sledge MK. 2005. Effects of culture media on the growth of Phymatotrichopsis omnivora. Phytopathology 95: S1112.

    Lee HK, Marek SM, Sledge MK. 2005. Scanning electron microscopy of infection of alfalfa roots by Phymatotrichopsis omnivora. Phytopathology 95: S1112.

    Littlefield LJ, Marek SM, Tyrl RJ, Winkelman KS. 2005. Morphological and molecular characterization of Puccinia lagenophorae, now present in central North America. Annals of Applied Biology 147: 35-42.

    Marek, SM. 2005. Molecular phylogeny of Phymatotrichopsis omnivora. Phytopathology 95: S65.

    Walker, NR, Marek, SM, and Taliaferro, CM. 2005. Colonization of bermudagrass roots produced from stolons by Ophiosphaerella herpotricha. Phytopathology 95: S107.

    Dhulipala M, Enis JN, Marek SM. 2004. Agrobacterium-mediated transformation of Phoma medicaginis. Phytopathology 94: S25.

    Marek SM, Wu J, Glass NL, Gilchrist DG, Bostock RM. 2003. Nuclear DNA degradation during heterokaryon incompatibility in Neurospora crassa resembles programmed cell death. Fungal Genetics and Biology 40: 126-137.

    Lee MH, Marek SM, Bostock RM. 2002. Redox regulation of Monilinia fructicola cutinase expression and germ tube development. Phytopathology Publication no. P-2002-0672-AMA.

    Marek SM, Pan Z, Ciuffetti LM, Bostock, RM. 2002. Agrobacterium tumefaciens-mediated transformation of Monilinia fructicola with green fluorescent protein. Phytopathology Publication no. P-2002-0673-AMA.

    Marek, S. M. and Bostock, R. M. 2000. Etiology of cold storage canker of fruit and nut trees in California. Phytopathology 90:S49. Publication no. P-2000-0348-AMA.

    Marek, SM, Roberts CA, Karr AL, Sleper DA. 2000. Chitinase activity in tall fescue seedlings as affected by cultivar, seedling development, and ethephon. Crop Science 40: 713-716.

    Marek, SM, Roberts CA, Beuselinck PR, Karr AL. 1995. Silver stain detection of chitinolytic enzymes after polyacrylamide gel electrophoresis. Analytical Biochemistry 230: 184-185.

    Roberts, CA, Marek SM, Wang L, Karr AL. 1994. Determination of chitinase activity in tall fescue by near infrared reflectance spectroscopy. Crop Science 34: 1070-1073.



    • Division of Agricultural Sciences and Natural Resources