Molecular aspects of somatic-to-embryogenic transition in plants
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REVIEW
Molecular aspects of somatic-to-embryogenic transition in plants Omid Karami & Behzad Aghavaisi & Aghil Mahmoudi Pour
Received: 14 June 2009 / Accepted: 25 August 2009 / Published online: 10 September 2009 # Springer-Verlag 2009
Abstract Somatic embryogenesis (SE) is a model system for understanding the physiological, biochemical, and molecular biological events occurring during plant embryo development. Plant somatic cells have the ability to undergo sustained divisions and give rise to an entire organism. This remarkable feature is called plant cell totipotency. SE is a notable illustration of plant totipotency and involves reprogramming of development in somatic cells toward the embryogenic pathway. Plant growth regularities, especially auxins, are key components as their exogenous application recapitulates the embryogenic potential of the mitotically quiescent somatic cells. It has been observed that there are genetic and also physiological factors that trigger in vitro embryogenesis in various types of plant somatic cells. Analysis of the proteome and transcriptome has led to the identification and characterization of certain genes involved in SE. Most of these genes, however, are upregulated only in the late developmental stages, suggesting that they do not play a direct role in the vegetative-to-embryogenic transition. However, the molecular bases of those triggering factors and the genetic and biochemical mechanisms leading to in vitro embryogenesis are still unknown. Here, we describe the plant factors that participate in the vegetative-to-embryogenic transition and discuss their possible roles in this process. O. Karami (*) Department of Biotechnology, Bu-Ali Sina University, Hamedan, Iran e-mail: [email protected] B. Aghavaisi Department of Agronomy, Bu-Ali Sina University, Hamedan, Iran A. Mahmoudi Pour Department of Horticulture, Bu-Ali Sina University, Hamedan, Iran
Keywords Somatic embryogenesis . Embryogenesis cell . Gene
Introduction Embryogenesis is a crucial developmental process in the life cycle of plants spanning the transition from the fertilized egg to the generation of a mature embryo. In this process, the embryo acquires a defined apical–basal pattern along the main body axis with shoot and root poles, a hypocotyl and cotyledons. Alternatively, embryogenesis can take place without the involvement of fertilization or gamete fusion. The origins of such asexual embryos are quite diverse; e.g., apomictic embryos are derived from an unfertilized egg cell or from maternal tissue. Somatic embryogenesis (SE) is the developmental restructuring of somatic cells toward the embryogenic pathway and forms the basis of cellular totipotency in higher plants [76, 130]. While carrot was the first plant species in which SE was reported, during the last 50-plus years of culturing experiments, the induction of in vitro SE has been shown to be successful in many plant species, including angiosperms and gymnosperms. SE provides an attractive model system for studying zygotic embryogenesis, particularly b
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