Somatic Embryogenesis in Arabidopsis thaliana Promoted by the Wuschel Homeodomain Protein

Abstract

Somatic embryogenesis is a unique pathway for asexual propagation or somatic cloning in plants. The developmental process of somatic embryogenesis shares considerable similarity with that of zygotic embryogenesis, and this is likely due to the conservation in the underpinning cellular and molecular mechanisms between the two processes. Therefore, somatic embryogenesis provides an attractive model system for studying zygotic embryogenesis, particularly because zygotic embryos are encased by maternal tissues and difficult to access by biochemical and molecular tools. Moreover, in biotechnological applications, most economically important crop as well as non-crop plants are regenerated via somatic embryogenesis. In contrast to organogenesis, which requires a high cytokinin to auxin ratio, somatic embryogenesis does not require any external cytokinins, but rather is dependent on high concentrations of 2,4-D, a synthetic chemical that has long been used as a functional analog of auxin. It is generally believed that somatic embryogenesis is mediated by a signaling cascade triggered by external auxin or 2,4-D. However, the signal transduction pathway, particularly the molecular mechanism involved in the transition of a vegetative cell to an embryogenic competent cell, remains largely unexplored.