Dissecting embryonic and seedling morphogenesis in Arabidopsis by promoter trap insertional mutagenesis

Development can be considered to comprise the co-ordinated regulation of patterning at different levels: patterning of cells to form tissues, patterning of tissues to form organs, and patterning of organs to generate the characteristic architecture of the organism. These processes are expected, in turn, to be mediated by the precise spatial and temporal regulation of patterns of gene expression during development, which depend on appropriate signalling mechanisms. In order to investigate molecular events of morphogenesis in plants, we have utilized a system of promoter trap insertional mutagenesis in Arabidopsis, to generate both phenotypic mutants and gene fusions that represent markers useful in studying the regulation of patterning. A screen of transgenic seedlings containing a T-DNA promoter trap has led to the identification of mutants defective in seedling shape and embryonic development, and of GUS fusion genes that are expressed in spatially restricted patterns. Mutants have been crossed with marker lines expressing cell type-specific GUS activities, to investigate their cellular organization. For example, the POLARIS marker gene is expressed in the embryonic and seedling root tip. When crossed with hydra, which lacks an embryonic root, and with emb30, which lacks both embryonic and seedling roots, it is nevertheless expressed in the correct relative position, and we hypothesize that it represents a novel marker of root positional information, independent of root morphogenesis.