Gene regulatory interactions at lateral organ boundaries in maize.

Maize leaves have distinct tissues that serve specific purposes. The blade tilts back to photosynthesize and the sheath wraps around the stem to provide structural support and protect young leaves. At the junction between blade and sheath are the ligule and auricles, both of which are absent in the recessive liguleless1 (lg1) mutant. Using an antibody against LG1, we reveal LG1 accumulation at the site of ligule formation and in the axil of developing tassel branches. The dominant mutant Wavy auricle in blade1 (Wab1-R) produces ectopic auricle tissue in the blade and increases the domain of LG1 accumulation. We determined that wab1 encodes a TCP transcription factor by positional cloning and revertant analysis. Tassel branches are few and upright in the wab1 revertant tassel and have an increased branch angle in the dominant mutant. wab1 mRNA is expressed at the base of branches in the inflorescence and is necessary for LG1 expression. wab1 is not expressed in leaves, except in the dominant mutant. The domain of wab1 expression in the Wab1-R leaf closely mirrors the accumulation of LG1. Although wab1 is not needed to induce lg1 expression in the leaf, LG1 is needed to counteract the severe phenotype of the dominant Wab1-R mutant. The regulatory interaction of LG1 and WAB1 reveals a link between leaf shape and tassel architecture, and suggests the ligule is a boundary similar to that at the base of lateral organs.