PHANTASTICA - A GENE REQUIRED FOR DORSOVENTRALITY OF LEAVES IN ANTIRRHINUM-MAJUS

To understand better the mechanisms that lead to dorsoventrality in th e lateral organs of plants, mutants at the phantastica (phan) locus of Antirrhinum majus have been identified and characterised. The leaves, bracts and petal lobes of phan mutants show varying degrees of reduct ion in dorsal tissues, indicating that phan is required for establishi ng dorsal cell identity, Each phan mutant produces a variety of differ ent leaf morphologies, but has a characteristic and relatively constan t floral phenotype, In several different forms of phan mutant leaves a nd petal lobes, novel boundaries between dorsal and ventral cell types form ectopic axes of growth, suggesting that phan-dependent dorsal ce ll identity is required for lateral growth of the wild-type leaf and p etal lobe. Comparisons between the development of wild-type and mutant petals or leaves reveal that phan acts early in development of these lateral organs. The possible role of the phan gene in evolution of dif ferent leaf forms is discussed.