Molecular overview on plant somatic embryogenesis.

Abstract The developmental pathway leading to plant somatic embryogenesis (SE) is true demonstration of totipotency of plant cells. During this process, somatic cells, under appropriate conditions, divide and differentiate into embryos. This developmental pathway plays an important role as an efficient means for plant regeneration and large-scale propagation. It includes a profound reprogramming of gene expression leading to changes in cell division and differentiation patterns, becoming a suitable platform to study the morpho-physiological and molecular aspects involved in plant cell differentiation and embryo development. Plant growth regulators such as auxin, as well as stress factors and DNA methylation, are key components to induce entry into SE pathways. Proteome and transcriptome analysis allowed isolation and characterization of embryogenic-specific gene markers involved in promoting vegetative-to-embryogenic transition as well as in maturation of somatic embryos contributing to the understanding of complex relationships between inductive conditions and somatic embryo formation. This review describes current advances made, mainly at the molecular level, in discovery of the main factors involved in the induction and maturation of somatic embryos providing a basic background for understanding genetic reprogramming that is at the heart of this process. We paid special attention to extracellular protein markers during SE as well as to auxin, abscisic acid and ethylene response genes, transcriptor factors and proteins involved in embryogenic competence acquisition.