Some Developmental and Molecular Aspects of Somatic Embryogenesis (Nonzygotic Embryogenesis)

The ability of plant cells to recapitulate embryo development via somatic embryogenesis (nonzygotic embryogenesis; see Chapter 14) has been utilized extensively to identify genes involved in plant embryogenesis. Proteins or genes expressed by embryos, embryogenic cells, and nonembryogenic cells have been compared. More recently, genetic approaches, mainly using Arabidopsis, have shown that mutations in single genes can lead to enhanced somatic embryogenesis directly in planta or in tissue culture. In Arabidopsis, other genes have been identified that upon ectopic expression result in spontaneous formation of somatic embryos directly from fully differentiated tissues. The purpose of this chapter is to discuss several of these recent studies. Most of the earlier work has been summarized in recent reviews (e.g., Mordhorst et al., 1997), and will only be briefly mentioned here.