MOLECULAR CONTROL OF FLORAL ORGANOGENESIS IN HIGHER-PLANTS - THE ABCDMODEL

Plants are an important group of organisms which are capable of auxotr ophic growth and therefore have a vital function to maintain life on e arth. Although a number of plant species reproduce asexually, most pla nt species use specialised structures, flowers, for sexual reproductio n. Compared with animal systems surprisingly little is known about the molecular processes governing organogenesis. However during the last five years a number of regulatory genes have been identified, isolated and characterized which are controlling the onset of developmental pr ogrammes leading to the determination and development of the various f loral organs. The function of these genes was studied using genetic an d molecular genetic techniques. Three classes of genes can be discrimi nated which are determining the developmental switches from vegetative meristem (class I), via floral meristem (class II) into the various o rgan primordia (class III). The genes involved encode transcription fa ctors which function in a complex network of regulatory proteins. The final fates of the floral organ primordia are determined by the so-cal led ABCD genes. The activity of those genes can be summarised in the A BCD model which provides a simplified way to describe how the identity of each floral organ is determined.