Molecular regulation of plant somatic embryogenesis

In vitro embryogenesis is an asexual reproduction process by which embryos are produced from either gametophytic (androecium/gynoecium) or sporophytic (somatic) tissues. Regardless of the type of explant used, the hallmark of this process is that the explant cells undergo dedifferentiation and acquire meristematic identity. The developmental program of such meristematic cells can then be redirected to form somatic embryos, depending on the imposed culture environment. Analysis of proteomes and transcriptomes has led to the molecular identification and functional characterization of many genes involved in the initiation and development of somatic embryos. These genes can be classified into three categories: embryonic induction, embryonic, and maturation. So far, few genes involved in early somatic embryogenesis have been characterized because isolation of early pure embryonic tissue is very difficult. This review focuses on genes regulating the induction process. Furthermore, we employed bioinformatic tools and pathway databases to identify genes that may play roles in regulating early somatic embryogenesis. A total of 51 proteins were identified that may function in early somatic embryogenesis. These proteins are predicted to be involved in hormone signal transduction, chromatin remodeling, cell cycle regulation, cellulose biosynthetic and metabolic activity, GTPase signal transduction, transcription regulation, meristem formation and maintenance, and/or apoptosis and microtubule organization. This review will help advance knowledge and promote research on molecular regulation of early somatic embryogenesis.