Michael P. Timko


  • PhD, Rutgers University

Primary Appointment

  • Professor, Biology


Research Interest(s)

Gene regulation during host-parasite interaction

Research Description

Research in my laboratory currently focuses on several very different aspects of plant cell growth and differentiation. One area of current interest is an examination of the biochemical, cellular, and genetic factors that regulate the biosynthesis of chlorophyll and other biologically relevant tetrapyrroles in higher plants, algae, and photosynthetic bacteria. We are particularly interested in process of protochlorophyllide reduction, the key regulatory step in the biosynthetic pathway. Two distinct biochemical routes for Pchlide reduction have evolved in nature. One mechanism, found in the cyanobacteria, green algae, non-vascular plants, gymnosperms and angiosperms, is catalyzed by a unique photoenzyme known as NADPH: protochlorophyllide oxidoreductase (POR) and is dependent on light for its action. The second mechanism, thought to be evolutionarily older because of its occurrence in the purple bacteria, reduces Pchlide to Chlide in a light-independent manner. Over the next several years we also hope to determine whether the different POR isoforms now known to exist in most plant species have non-redundant functions during chloroplast development and, if so, to define these roles(s) in the context of chloroplast development and overall photomorphogenesis. Future work will also involve a detailed analysis of structure-function relationships in the vascular plant PORs. In addition to our work on the light-dependent POR enzyme, a major new effort is now underway in my laboratory using Chlamydomonas reinhardtii as a model organism to understand the process of light-independent chlorophyll formation and the factors involved in its regulation.

A second major area of research in the laboratory is examination of the mechanisms controlling cellular differentiation in the parasitic angiosperm Striga asiatica, and the molecular genetic basis for resistance to Striga parasitism in host and non-host crop species. The parasitic angiosperms are a diverse group of highly specialized organisms that derive all or part of their nutrition from other plant species. As a group, these plants constitute one of the major problems facing agricultural advancement in developing nations. Therefore, understanding the biology of these parasitic plants and the processes of host-parasite communication have merit at both the basic and applied level.

In addition to these two areas of investigation, a more recent area of study in my laboratory is an examination of the molecular genetic factors that regulate the formation of nicotine and related tropane alkaloids during plant senescence and as a consequence of pathogen attack. The biosynthesis of alkaloids in tobacco, as in most higher plants, is a developmentally activated process involving differential gene expression in specific tissues and cell types. In our studies, we are analyzing the nature and complexity of gene expression in the roots of maturing tobacco plants after removal of the flowering head (i.e., topping) using currently available PCR-based mRNA differential display technology. We are also examining the nature of differential gene expression in the roots and leaves of mature tobacco during the normal maturation and senescence, during induced senescence (e.g., following topping), and in response to wounding. Understanding the molecular basis for differential gene expression during tobacco growth and development is a fundamental requirement for designing successful strategies for the manipulation of leaf alkaloid contents.

Finally, in collaboration with Dr. Barbara Mann (Department of Medicine, UVA Health Sciences Center) we are testing the feasibility of producing recombinant GAL adhesin from E. histolytica in transgenic plants and the ability of this plant-derived protozoan protein to elicit oral immunization to amebiasis in animal (gerbil) model systems. If successful our proposed studies could provide the basis for the development of a plant-derived oral vaccine.

Selected Publications

  • Rabara R, Tripathi P, Reese R, Rushton D, Alexander D, Timko M, Shen Q, Rushton P. Tobacco drought stress responses reveal new targets for Solanaceae crop improvement. BMC genomics. 2015;16 484. PMID: 26123791 | PMCID: PMC4485875
  • Wang W, Liu G, Niu H, Timko M, Zhang H. The F-box protein COI1 functions upstream of MYB305 to regulate primary carbohydrate metabolism in tobacco (Nicotiana tabacum L. cv. TN90). Journal of experimental botany. 2014;65(8): 2147-60. PMID: 24604735 | PMCID: PMC3991746
  • Yang Z, Wafula E, Honaas L, Zhang H, Das M, Fernandez-Aparicio M, Huang K, Bandaranayake P, Wu B, Der J, Clarke C, Ralph P, Landherr L, Altman N, Timko M, Yoder J, Westwood J, dePamphilis C. Comparative transcriptome analyses reveal core parasitism genes and suggest gene duplication and repurposing as sources of structural novelty. Molecular biology and evolution. 2014;32(3): 767-90. PMID: 25534030 | PMCID: PMC4327159
  • Sears M, Zhang H, Rushton P, Wu M, Han S, Spano A, Timko M. NtERF32: a non-NIC2 locus AP2/ERF transcription factor required in jasmonate-inducible nicotine biosynthesis in tobacco. Plant molecular biology. 2013;84(1): 49-66. PMID: 23934400
  • Mellor K, Hoffman A, Timko M. Use of ex vitro composite plants to study the interaction of cowpea (Vigna unguiculata L.) with the root parasitic angiosperm Striga gesnerioides. Plant methods. 2012;8(1): 22. PMID: 22741546 | PMCID: PMC3441300
  • Wickett N, Honaas L, Wafula E, Das M, Huang K, Wu B, Landherr L, Timko M, Yoder J, Westwood J, dePamphilis C. Transcriptomes of the parasitic plant family Orobanchaceae reveal surprising conservation of chlorophyll synthesis. Current biology : CB. 2011;21(24): 2098-104. PMID: 22169535
  • Zhang H, Bokowiec M, Rushton P, Han S, Timko M. Tobacco transcription factors NtMYC2a and NtMYC2b form nuclear complexes with the NtJAZ1 repressor and regulate multiple jasmonate-inducible steps in nicotine biosynthesis. Molecular plant. 2011;5(1): 73-84. PMID: 21746701
  • Hernandez-Garcia C, Bouchard R, Rushton P, Jones M, Chen X, Timko M, Finer J. High level transgenic expression of soybean (Glycine max) GmERF and Gmubi gene promoters isolated by a novel promoter analysis pipeline. BMC plant biology. 2010;10 237. PMID: 21050446 | PMCID: PMC3095320
  • Westwood J, Yoder J, Timko M, dePamphilis C. The evolution of parasitism in plants. Trends in plant science. 2010;15(4): 227-35. PMID: 20153240
  • Li J, Timko M. Gene-for-gene resistance in Striga-cowpea associations. Science (New York, N.Y.). 2009;325(5944): 1094. PMID: 19713520