Regulation of somatic embryogenesis in crops: A review

‘Somatic embryogenesis’ is a process whereby somatic cells differentiate into somatic embryos. It is regulated by several factors, including phytohormones, proteins, transcription factors, and other related substances during different stages of development. Somatic cells are not terminally differentiated and therefore regain totipotency to initiate embryo development. Although this phenomenon is well known, the detail mechanism of how hormones specify cell fate during in vitro organogenesis is still mysterious. To uncover this mechanism, several studies have been done using biochemical, biological and molecular approaches with embryo-defective mutants or somatic embryogenesis. Recent progress in plant molecular and developmental biology now allows us to establish new pathways for the transition of somatic cells to the embryogenic state. Hormone signaling plays an important role in the cell differentiation during different stages of embryogenesis. During somatic embryo induction, there is differential gene expression resulting in synthesis of new mRNAs and proteins. An array of genes activated or differentially expressed during somatic embryogenesis have been isolated. Few transcription factors have been identified from embryo-defective mutants and some regulatory factors (phenolic compounds and peptidyl growth factors) were detected from culture medium during somatic embryogenesis. In future, research on characterization of development-specific genes during somatic embryogenesis may elucidate a deeper insight in understanding the mechanisms involved during differentiation of somatic cells and phenotypic expression. This review summarizes current understanding of the cellular and molecular aspects of SE and various regulating factors affecting it.