Mutations in the rice liguleless gene result in a complete loss of the auricle, ligule, and laminar joint

The area between the upper part of the leaf sheath and the basal portion of the leaf blade contains several specialized organs, such as the laminar joint, auricle and ligule. Here we report the identification of T-DNA insertional mutant lines that lack all of these organs. The gene knocked out in the mutant lines encodes a protein that contains a SBP (SQUAMOSA promoter Binding Protein)-domain and is highly homologous to the maize LIGULELESS1 (LG1) gene. At the amino acid sequence level, the OsLG1 protein is 69% identical to maize LG1 and 78% identical to barley LG1. We named the rice gene OsLIGULELESS1 (OsLG1). Transient expression of an OsLG1:RFP (Red Fluorescent Protein) fusion protein indicated that the protein is localized to the nucleus. Transgenic plants harboring the OsLG1 promoter:GUS (beta-glucuronidase) reporter gene construct display preferential expression in developing laminar joint regions and meristemic regions. The gene is also weakly expressed in the ligule, auricles, and leaf sheaths at the basal region. These results indicate that OsLG1 is a transcriptional factor that plays an important role in building the laminar joint between leaf blade and leaf sheath boundary, thereby controlling ligule and auricle development.