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Todd J. CookeProfessorPh.D. - Cornell University, 1979Telephone: (301) 405-1628 Fax: (301) 314-9082 E-mail: tjcooke@umd.edu Research Interests: Plant development and evolution, generation of biological form, developmental mechanisms operating in the origin and diversification of land plants, nature of multicellularity My students and I are currently studying three great questions in biology: 1) generation of form, 2) origin of land plants, and 3) nature of multicellularity. Because the primary objective of the graduate program in our lab is to train independent and creative scientists, each student is strongly encouraged to design his/her own research project to address one of these questions. These projects are carried out on a wide range of green plants by using appropriate techniques from developmental biology, biophysics, genetics, analytical biochemistry, and other disciplines. 1) Generation of biological form (morphogenesis) - Research problems in plant morphogenesis are especially challenging because morphogenetic processes appear to depend not only on specific gene expression being regulated in time and space but also on physicochemical mechanisms capable of operating on all living and non-living structures. For example, current graduate student Wanda Kelly is investigating leaf arrangement (also known as phyllotactic patterning) in aquatic plants, which are quite unique because they have the potential to arrange their leaves in either Fibonacci spirals or non-Fibonacci whorls. In essence, in spiral phyllotaxis, if the leaves are assigned a number in the order of their origin, then the intervals in the numbers between successive leaves in each spiral can be related to the enigmatic Fibonacci series (1, 1, 2, 3, 5, 8, 13, etc.). By contrast, the leaves in whorled phyllotaxis are arranged in stacked rings encircling the axis. It appears very likely that her studies of these plants have led Wanda to discover the elusive geometrical principles underlying the phyllotactic patterning of all plants. She received the Katherine Esau Award for best student paper from the Developmental and Structural Section at the 2003 Annual Meeting of the Botanical Society of America. She is presently attempting to determine which gene products are capable of interpreting those geometrical principles so that they can mediate the phyllotactic patterns observed in plants.
2) Novel developmental mechanisms in the origin and diversification of land plants - The successful invasion of the terrestrial environment by certain charophycean green algae represented in a pivotal event in the evolution of life. We are very interested in how evolutionary contingency (i.e., the genetic, developmental, and physiological toolkits already present in those ancestral algae) and subsequent innovation resulted in novel developmental mechanisms that were operating in the evolution of early land plants. We are devoting particular emphasis to the small bryophytes (hornworts, liverworts, mosses), which represent the most ancient lineages of living land plants. For example, current graduate student DorothyBelle Poli is studying how these bryophytes generate post-embryonic axes, which is the key process for constructing plant bodies. In contemporary vascular plants (e.g., ferns, gymnosperms, flowering plants), axis formation is regulated by polar transport of the hormone auxin (indole-3-acetic acid) via specific transmembrane proteins; therefore, DB decided to investigate the mechanism of auxin movement in bryophyte axes. She discovered a well-defined sequence of incremental evolution in auxin movement mechanisms within the bryophytes: simple diffusion in hornworts, facilitated apolar diffusion in liverworts, and genuine polar transport in mosses. One plausible interpretation of these observations is that the earliest land plants evolved increasingly sophisticated mechanisms for regulating axis formation, with the common ancestor of the moss-vascular plant lineage evolving a hormonal mechanism preadapted for constructing the long axes of vascular plants. DB received the A. J. Sharp Award for best student paper from the Bryological and Lichenological Section at the 2003 Botanical Society Annual Meeting. She was also invited to present her work as a symposium talk at the Moss 2003 meetings.
Poli, DB, Jacobs, M, and Cooke, TJ. 2003. Auxin regulation of axial growth in bryophyte sporophytes: Its potential significance for the evolution of early land plants. American Journal of Botany 90: 1405-1415. (article 3) Cooke, TJ, Poli, DB, and Cohen, JD. 2003. Did auxin play a crucial role in the evolution of novel body plans during the late Silurian-early Devonian radiation of land plants? In: AM Hemsly and I Poole, eds. The Evolution of Plant Physiology, pp. 85-107. Academic Press: London. (article 4) 3) Nature of multicellularity - At least 10 lineages of unicellular eukaryotes have independently evolved multicellular species. We are intrigued by the question of how did these different lineages solve common problems such as developmental integration, intercellular communication, and nutrient transport, which are intrinsic to multicellular organisms. Just to cite one example, multicellular animals are characterized by early segregation of germ cells from the somatic cells that differentiate to form the animal body. Animal somatic cells, with the notable exception of some stem cells, tend to have very restricted developmental fates. By contrast, multicellular plants are characterized by delayed segregation of the germ line, with the consequence that all nucleate cells in the plant body retain their totipotency, i.e., the ability of a single cell to regenerate into an entire organism. Two former graduate students, David Ribnicky and Ester Sztein, investigated certain aspects of the hormonal regulation of plant totipotency in developing embryos and wounded plant parts. respectively. They showed that the initial response to either fertilization or wounding appears to be a rapid surge in the activity of the tryptophan-dependent pathway for auxin biosynthesis. This pathway produces superoptimal hormone levels, which may be necessary for initiating the cell proliferation stage of the totipotent response. Future work on this question may also focus on the role of intercellular communication in the in situ suppression of plant totipotency.
Sztein, AE, Cohen, JD, and Cooke, TJ. 2002. Indole-3-acetic acid
biosynthesis in isolated axes from germinating been seeds: The
effect of wounding on biosynthetic pathway. Plant Growth Regulation
36: 201-207. (article
6) Recent Ph.D. students (degree year, dissertation topic, and present position)
Teaching responsibilitiesI am currently teaching an undergraduate majors course entitled BSCI 225 Introductory Plant Biology as well as graduate seminars focusing on recent advances in hormone physiology, molecular genetics, developmental mechanisms and macroevolutionary processes in plants.Major awards
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