Plant Embryogenesis (Zygotic and Somatic)

Abstract Zygotic embryogenesis in higher plants describes the developmental period in which the zygote undergoes a series of differentiation events, leading to the formation of a mature embryo. Establishment of the major embryonic organs and shoot and root apical meristems occur though partitioning events along the apical–basal axis, and many of these events are guided by the hormone auxin . Formation of the three embryonic tissue systems occurs along a radial axis perpendicular to the apical–basal axis. The mature zygotic embryo is generally developmentally arrested, metabolically quiescent and enclosed within maternal tissues of the seed. Somatic cells can be induced to divert from their normal fate and develop into embryos in a process termed somatic embryogenesis. Auxin and other plant hormones appear to play critical roles in inducing embryogenic competence. Zygotic and somatic embryogenesis represent parallel developmental programs in which cells acquire embryogenic cell fate and develop into mature embryos. Key Concepts: Embryo development can be divided into two phases: the morphogenesis phase in which the basic body plan of the embryo is established, and the maturation phase in which the embryo becomes tolerant of desiccation and accumulates storage macromolecules such as lipids, proteins and starch. During its development, the embryo is divided into distinct domains along its apical–basal and radial axes. Plant embryo formation represents a series of partitioning events in which organs and tissues are formed from larger domains. Cell fate within the embryo is largely dependent on the position of the cell within the embryo body. Plant cells are totipotent and have the ability to regenerate a fully differentiated organism. Somatic embryos follow similar developmental patterns to their zygotic counterparts, and they occur naturally or are induced in culture. Establishment of embryogenic competence occurs before the formation of the somatic embryo.