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October 20, 2006

Dead Embryos Tell Tales: Dissection of Embryogenesis in Arabidopsis


John J. Harada

Section of Plant Biology, College of Biological Sciences, One Shields Avenue, University of California, Davis, CA 95616

In higher plants, seed development is initiated with a double fertilization event that gives rise to the diploid zygote and the triploid endosperm.  The single-celled zygote then enters a phase of morphogenesis in which the basic body plan of the plant is established with fixation of the shoot-root axis, differentiation of the embryonic tissue systems, and formation of the shoot and root apical meristems and the embryonic organs.  Late in embryogenesis, embryos enter the maturation phase in which they accumulate storage macromolecules and acquire the ability to withstand desiccation.  To define genes that are required to make a seed and obtain insight into their roles in embryo and seed development, we have profiled RNA populations from Arabidopsis seeds at various stages of development.  We have also characterized representative RNA populations at the other stages of the life cycle to identify genes expressed specifically during seed development and to determine the expression pattern of genes expressed at other stages of development.  Our analysis of these data and use of the results to identify regulators of seed development will be discussed.


A number of different cell types in higher plants can undergo embryo development.  In addition to zygotic embryogenesis, embryos can be formed through somatic embryogenesis, microspore embryogenesis, and a suite of processes collectively known as apomixis.  To define mechanisms involved in the control of embryonic cell fate, we are studying the Arabidopsis LEAFY COTYLEDON (LEC) genes. The LEC genes, LEC1, LEC2, and FUSCA3, play essential roles in several aspects of embryogenesis.  Moreover, ectopic expression of these genes induces embryonic characteristics and somatic embryo formation in vegetative cells.  Insights into the mechanisms by which a cell is programmed to undergo embryogenesis will be discussed.