Molecular analysis of somatic embryogenesis: An overview

Somatic embryogenesis (SE) was discovered in the 50's and it has viewed as a promissory tool for massive propagation of commercial crops and as a potential model to study cellular differentiation in plants. The first evidence of differential gene expression during SE came in the 80's and up to date a large number of genes, whose expression varies during the induction and development of somatic embryos, have been cloned and studied. The objective of the present review is to show a molecular analysis of somatic embryogenesis paying special attention to three fundamental stages: (i) the onset, where reported results suggest the existence of a signalization/reception process leading the somatic cell to a reprogramming toward a new embryogenetic program, (ii) the transition of embryos through the characteristic stages where organ are formed and the body plan is established and (iii) maturation where a large number of LEA and ABA-regulated genes have been cloned and studied. Finally, an analysis of other cloned genes, as those coding for heat shock proteins that can help to form a somatic embryo, is presented and some basic unexplored aspect of somatic embryogenesis are discussed.