molecular biology and genetic utility of transposons in plants
	Stephen Dellaporta, Ph.D. Professor of Molecular, Cellular & Developmental Biology Room: OML 450A Phone: (203) 432-3895 Fax: (203) 432-3879 Email: stephen.dellaporta@yale.edu Web site B.Sc. University of Rhode Island 1978; Ph.D. Worcester Consortium 1981

Our lab studies the molecular biology and genetic utility of transposons in plants. On-going experiments investigate the developmental and biochemical regu-lation of transposition and the utility of plant transposable elements for gene isolation and enhancer trap screening in both Arabidopsis and maize. These studies employ the transposable element system Ac/Ds. The autonomous Ac element encodes a transposase required for auto-transposition and for the transactivation of non-autonomous Ds elements.

Past studies have been aimed at determining the requirements for Ac transposition.These include demonstrating that transposition is coupled to the period of chromosomal DNA replication, exam-ining the tendency for Ac to transpose over short physical distances, and detecting that transposed elements often insert into hypermethylated regions of the chrom-osome. These factors may reflect constraints on target site choice. Epigenetic changes in Ac activity have been associated with a co-suppression phenomenon associated with methylation of Ac sequences during plant devel-opment. This basic information about Ac transposition has assisted us in developing genetic and molecular strategies for extending transposition studies to heterologous species such as Arabidopsis.

In Arabidopsis and maize, efforts are underway toward saturation mutagenesis of the plant genome with genetically engineered Ac/Ds elements. Heterologous transposition systems employ positive-negative selections and synthetic Ds elements with enhancer trap capabilities. These elements have been introduced into the Arabidopsis genome and over the next several years our goals are to define the genetic pathways controlling late developmental processes during flowering such as gamete formation and fertilization. Furthermore, these heterologous transpo-sition systems will be used to further define the mechanism and cellular functions required for transposition in plants.

In maize, our insertional mutagenesis program has uncovered an array of mutations in seed, plant and floral development. Using Ac probes, several genes have been cloned and studied, particularly genes involved in the late flowering process of sex determination. Unisexual inflorescences and flowers are produced by the selective abortion of either stamen or pistil primordia during floral development.

The Tassel-seed genes of maize are major regulators of programmed organ death of the gynoecium, a process leading to the sexual dimorphic state of the terminal inflorescence. The Tassel-seed:2 gene has been cloned by Ac tagging and shown to be expressed in the subepidermal cells of developing gynoecia. This subepidermal expression leads to unisexual flowers by programming developmental arrest and abortion of performed floral organs. We are now in the process of determining the cellular and biochemical basis of programmed organ death mediated by tassel-seed genes.

Selected Publications

Dellaporta, S.L. and Calderon-Urrea. (1994). The sex determination process in maize. Science 266:1501-1505

Walker, E.L., Robbins, T.P., Bureau, T.E., Kermicle, J., and Dellaporta, S.L. (1995). Transposon-mediated chromo-somal rearrangements and gene duplications in the formation of the maize R-r complex. EMBO J.14:2350-2363.

Ronemus, M., Galbiati, M., Ticknor, C., Chen, J., and Dellaporta, S.L.(1996). Demethylation-induced developmental pleiotropy in Arabidopsis. Science, 59: 2798-2801.

Liu, S. , J. Widom, C.W. Kemp, C.M. Crews, and J. Clardy. (1998) Atomic Structure of Human Methionine Aminopeptidase 2 Complexed with the Angiogenesis Inhibitor Fumagillin. Science 282:1324-1327.

top