Embryogenesis,a process of pattern formation

Plant embryogenesis is traditionally defined as a developmental process from zygote to mature embryo,which has the potential to form a complete plant(Bhojwani,1974;Hu,2005).In dicotyledonous species,the fertilized egg or zygote usually divides according to a stereotyped pattern and gives rise to an embryo that consists of an embryonic shoot,cotyledons,hypocotyls,and an embryonic root.Thus,the basic body plan of the plant is established during the embryogenesis.Interestingly,the shoot-leaf-stem structure,not including the root,is repeatedly photocopied as a basic unit throughout plant vegetative growth(Wolpert et al.,2002).In this case,embryogenesis is a seemingly endless process and the epitome of plant body-building.However,recent studies on the molecular mechanism of embryogenesis revealed that the basic plant body plan is laid down as the establishment of the radial and apical-basal axes.During this process,both the radial concentric tissue layers and the apicalbasal sections of the plant body are generated,especially the root and shoot stem cell pools,which are essential for postembryonic growth(De Smet and Jürgens,2007;De Smet et al.,2010).All further development and morphogenesis are governed or guided by this basic pattern.Thus,embryogenesis is,in fact,a process of pattern formation.