Uncovering the post-embryonic role of embryo essential genes in Arabidopsis using the controlled induction of visibly marked genetic mosaics: EMB506, an illustration.

The embryo essential gene EMB506 plays a crucial role in the transition of the Arabidopsis embryo from radial symmetry to bilateral symmetry just prior to the early heart stage of development. In addition to influencing embryo development EMB506 also affects chloroplast biogenesis. To further investigate the role of EMB506 gene expression in Arabidopsis we have generated green fluorescent protein (GFP) marked emb506 mosaic sectors at temporally defined stages during embryogenesis and additionally during various stages of vegetative growth, in otherwise phenotypically wild-type plants. We confirm the essential requirement for EMB506 gene expression in chloroplast biogenesis as reflected by the decreased chlorophyll content in emb506 mosaic sectors. We also show that the influence of EMB506 gene expression as it impinges on chloroplast biogenesis is first relevant at an intermediate stage in embryogenesis and that the role of EMB506 gene expression in chloroplast biogenesis is distinct from the essential role of EMB506 gene expression during early embryo development. By inducing emb506 mosaicism after the essential requirement for EMB506 gene expression in embryogenesis and also during vegetative growth we reveal that EMB506 gene expression additionally is required for correct cotyledon-, true leaf- and cauline leaf margin development. The strategy that we describe can be tailored to the mosaic analysis of any cloned EMB gene for which a corresponding mutant exists and can be applied to the mosaic analysis of mutant lethal genes in general.