Control of Embryo Development in Higher Plants

University Of California-Davis, Davis CA

Investigators

Abstract

PI: John J. Harada December 1, 2003 Control of Embryo Development in Higher Plants Page 3 NSF 0344753 ABSTRACT Embryogenesis describes the period of the plant life cycle during which a single-celled zygote undergoes a series of differentiation events, resulting in the formation of a mature and metabolically quiescent embryo. Embryogenesis in higher plants consists of two conceptually distinct phases. The earliest is the morphogenesis phase during which the basic body plan of the plant is formed. This is followed by the maturation phase during which the embryo accumulates proteins and lipids, induces processes that allow them to withstand desiccation, and becomes metabolically quiescent. There are two major goals of this proposal. One objective is to understand how these two embryonic phases are coordinated. The maturation phase evolved to permit higher plants to make seeds. Given that lower plants do not undergo maturation or make seeds, it is likely that, in higher plants, the maturation phase was inserted into a continuous phase of morphogenesis. The second objective is to define the developmental processes that allow cells to change their fate and enter into an embryonic mode of development. A diversity of higher plant cell types can be induced to undergo embryogenesis. Although it is known that many of these embryos follow similar morphogenetic pathways, virtually nothing is known of the molecular processes that allow these cells to initiate embryonic programs. We will address these problems using Arabidopsis LEAFY COTYLEDON2 (LEC2). LEC2 encodes a protein that regulates the transcription of other genes and is a central regulator of embryogenesis required for processes that occur during both the morphogenesis and maturation phases. For example, we have shown that overexpression of the LEC2 gene activates maturation processes in vegetative and reproductive organs and induces somatic embryo formation from vegetative cells. This proposal addresses the overall question of how LEC2 establishes an environment that activates the maturation program and promotes cellular competence to undergo somatic embryogenesis. An immediate objective is to identify genes directly regulated by the LEC2 transcription factor. The spectrum of genes activated and repressed should provide insight into the regulatory programs directly controlled by LEC2. A second aim is to identify other embryonic regulators that work in concert with LEC2 to discover other participants in the regulatory network controlling embryogenesis. Together, these experimental approaches should provide new insights into the control of embryo development. In addition to providing new basic knowledge about higher plant embryogenesis, information derived from these studies may be relevant to the design of strategies to manipulate seed development for applied purposes. The educational value of the project is that it will provide strong training opportunities for undergraduate, graduate students, and high school students.