THE MAIZE MUTANT NARROW SHEATH FAILS TO ESTABLISH LEAF MARGIN IDENTITY IN A MEROSTEMATIC DOMAIN

The maize mutant narrow sheath (ns) displays a leaf shape and plant st ature phenotype that suggests the preprimordial deletion of a leaf dom ain. The ns mutant phenotype is inherited as a recessive, duplicate-fa ctor trait, conditioned upon homozygosity for each of the two unlinked mutations narrow sheath-1 (ns1) and narrow sheath-2 (ns2). Mutant lea ves are missing a large domain including the leaf margin, and mutant i nternodes are shortened on the marginal side of the stem. This domain deletion extends from the internode to beyond the longitudinal mid-len gth of the blade, and corresponds to an alteration in the organization of a specific region of the shoot apical meristem. The premargin regi on of mutant founder cells fail to down-regulate expression of Knox ge nes, markers of nonleaf meristematic identity. Our results indicate th at leaf domains may acquire identity in the meristem itself, and that the subdivision of preprimordial developmental fields into differentia l domains is a common feature of both plant and animal organogenesis.