LIGULELESS1 ENCODES A NUCLEAR-LOCALIZED PROTEIN REQUIRED FOR INDUCTION OF LIGULES AND AURICLES DURING MAIZE LEAF ORGANOGENESIS

The maize ligule and auricle are structures on the maize leaf that dev elop at the boundary of the sheath and blade. In the absence of ligule less1 (Ig1) gene expression, ligule and auricle are not formed, and th e blade-sheath boundary does not develop as an exact line between shea th and blade. By using the Activator (Ac) transposable element as a mo lecular tag, a novel Ig1 allele, Ig1-m1, was isolated and cloned. Anal ysis of somatic revertant sectors confirmed that the LG1 gene product functions in a cell-autonomous fashion. cDNA cloning as well as RT-PCR analysis of the LG1 mRNA indicate that the Ig1 gene is expressed at v ery low levels in the ligular region of developing maize leaf primordi a, perhaps as early as plastochron 6 or earlier. Cellular localization studies in a heterologous system indicate that the LG1 product locali zes exclusively to the nucleus. The predicted amino acid sequence of t he LG1 protein is largely novel but contains an internal domain of 77 amino acids with significant similarity to a domain present in two rec ently identified SQUAMOSA PROMOTER-BINDING proteins 1 and 2 (SBP1 and SBP2) in Antirhinum majus.