9603821 Meyerowitz Technical This research is directed toward revealing the genetic and molecular mechanisms by which Arabidopsis flowers develop. The experiments are divided into two areas. The first area is to understand the regulation and function of the floral organ identity genes APETALA3 and PISTILLATA. The genes code for MADS-box DNA-binding proteins, and the proteins bind DNA as a heterodimer. The research is: to find the genes that specify the initial expression pattern of the two genes, which will be done by mutagenesis of transgenic lines that will give novel phenotypes if either MADS-box gene is ectopically activated; and to find the downstream genes activated or repressed by the AP3/PI heterodimer by use of differential display-RT-PCR methods. The second area is to derive a general model for the control of pattern of cell division in shoot and floral meristems. This will be done by the molecular cloning of the CLAVATA1, CLAVATA3 and WIGGUM genes. Non-technical An unanswered question in the genetic analysis of development is that of pattern formation: How does a collection of equivalent cells such as a plant flower primordium or a vertebrate limb bud become spatially organized, so that it develops into a highly patterned collection of different cell types? At least two processes are involved: patterned cellular differentiation, to give the final pattern of cell types, and patterned cell division, to give the appropriate size and shape to the mature structure. Flowers provide a particularly good example of these aspects of pattern formation; flowers usually have a stereotyped pattern of organ types: sepals, petals, stamens, and central carpels. Many flowers also have defined numbers of each of these organ types. The flower of Arabidopsis thaliana plants, for example, has four sepals spaced evenly around the floral periphery, four petals interior to and alternate with the sepals, six stamens, and a compound ovary of two carpels. The experiments described here will reveal some of the cellular mechanisms by which cells are directed to divide in appropriate patterns in developing flowers, and by which they are instructed to differentiate into appropriate cell types for their positions. If they succeed, the research will result in new genetic and molecular models for the spatial control of organ identity, and for the spatial patterning of cell divisions in plant pattern formation. These models will, in turn, reveal the genetic principles of plant development, and will, in the future, enable experimental control of plant development.
