THE PHANTASTICA GENE ENCODES A MYB TRANSCRIPTION FACTOR INVOLVED IN GROWTH AND DORSOVENTRALITY OF LATERAL ORGANS IN ANTIRRHINUM

The organs of a higher plant show two fundamental axes of asymmetry: p roximodistal and dorsoventral. Dorsoventrality in leaves, bracts, and petal lobes of Antirrhinum majus requires activity of the PHANTASTICA (PHAN) gene. Conditional mutants revealed that PHAN is also required f or earlier elaboration of the proximodistal axis. PHAN was isolated an d shown to encode a MYB transcription factor homolog. PHAN mRNA is fir st detected in organ initials before primordium initiation. The struct ure and expression pattern of PHAN, together with its requirement in t wo key features of organ development, are consistent with a role in sp ecifying lateral organ identity as distinct from that of the stem or m eristem. PHAN also appears to maintain meristem activity in a non-cell -autonomous manner.