DISSECTION OF SEXUAL ORGAN ONTOGENY - A GENETIC-ANALYSIS OF OVULE DEVELOPMENT IN ARABIDOPSIS-THALIANA

Understanding organogenesis remains a major challenge in biology. Spec ification, initiation, pattern formation and cellular morphogenesis, h ave to be integrated to generate the final three-dimensional architect ure of a multicellular organ, To tackle this problem we have chosen th e ovules of the flowering plant Arabidopsis thaliana as a model system , In a first step towards a functional analysis of ovule development, we performed a large-scale genetic screen and isolated a number of ste rile mutants with aberrant ovule development. We provide indirect gene tic evidence for the existence of proximal-distal pattern formation in the Arabidopsis ovule primordium. The analysis of the mutants has ide ntified genes that act at an intermediate regulatory level and control initiation of morphogenesis in response to proximal-distal patterning . A second group of genes functions at a subordinate control level and regulates general cellular processes of morphogenesis. A large group of male and female sterile mutants shows defects restricted to early o r late gametogenesis. In addition, we propose that the mature ovule ob tains its overall curved shape by at least three different processes t hat act in only one domain of the ovule.