Pattern formation in the Arabidopsis embryo: a genetic perspective.

During embryogenesis, a single cell gives rise to different cell types, tissues and organs which are arranged in a biologically meaningful context, or pattern. The resulting basic body organization of higher plants, which is expressed in the seedling, provides a reference system for postembryonic development during which the meristems of the shoot and the root produce the adult body. The seedling may be viewed as the superimposition of two patterns: one along the apical-basal axis of polarity and the other perpendicular to the axis. To analyse mechanisms underlying pattern formation in the embryo, a genetic approach has been taken in Arabidopsis. Mutations in a small number of genes alter one or the other of the two patterns. The mutant phenotypes suggest that early partitioning of the axis is followed by region-specific development, including the formation of the primary shoot and root meristems. The cloning of two genes involved in pattern formation provides a basis for mechanistic studies of how cells adopt specific fates in the developing embryo.