'Institute of Systematic Botany, University of Mainz, 55099 Mainz, Germany 2 Section of Plant Biology, University of California, Davis, CA 95616, USA 3 Department of Agronomy and Range Science, University of California, Davis, CA 95616, USA

摘要: The higher plant shoots are generally radially symmetrical; leaves produced at the shoot apex are dorsiventral while axillary shoots again show radial symmetry. Recently analyzed mutants in different plants indicate that the proper definition of adaxial and abaxial identities is necessary to generate a leaf margin and dorsiventral symmetry. Two genes important in the regulation of transsectional leaf symmetry are PHANTASTICA (a MYB (Myeloblastosis oncogene)-domain transcription factor) and KNOTTED1-like genes (homeodomain transcription factors). We review these results in light of hypotheses about the evolutionary origin of leaves and discuss similarities of mutant phenotypes to unifacial leaves occurring in extant taxa. Related symmetry phenomena of flattened shoots and parallels to the acquisition of dorsal and ventral identities in Drosophila wing imaginal discs are pointed out.