Gene Expression during Pseudotsuga Menziesii Embryogenesis: Low Molecular Weight Proteins

Abstract

Somatic embryogenesis refers to the process by which embryos are initiated from a single cell or previously differentiated somatic cells. Since first reported in Picea abies (Hakman et al., 1985), somatic embryogenesis has been described in a number of conifer species (Tautorus et al., 1991). Progress has since been made in the development of protocols for production of superior quality somatic embryos with improved germination rates. These include modification of culture medium by optimizing phytohormone concentration (Gupta and Pullman, 1994) and osmolarity content (Attree and Fowke, 1993), and desiccation treatments (Beardmore and Charest, 1995; Roberts et al., 1990). Presently, somatic embryogenesis is being used as an alternative means for rapid multiplication and large-scale production of superior materials to the commercial conifer forest (Attree and Fowke, 1993). The ability of somatic embryos to become embryogenic under defined condition relies on reprogramming of gene expression and triggers many structural changes which are similar to those found in zygotic embryos (Misra, 1994, 1995; Tautorus et al., 1991). As a result, somatic embryos have provided an excellent system to obtain information on the morphological, biochemical and molecular changes, which take place during embryo formation and during early events of embryogenesis. Moreover, the ability to stably transform and subsequently regenerate transgenic conifers, when somatic embryos are used as target materials in transformation via particle bombardment and Agrobacterium-mediated transformation, has recently been described (Bommineni et al., 1998; Levée et al., 1997). The use of conifer transformation along with the information on embryogenesis-specific genes will contribute a great deal to genetic engineering of commercially improved conifers and to elucidation of gene regulation occurring during conifer embryogenesis.