Gnarley1 is a dominant mutation in the knox4 homeobox gene affecting cell shape and identity

Maize leaves have a stereotypical pattern of cell types organized into disc rete domains. These domains are altered by mutations in knotted1 (kn1) and knox (for kn1-like homeobox) genes. Gnarley (Gn1) is a dominant maize mutan t that exhibits many of the phenotypic characteristics of the kn1 family of mutants. Gn1 is unique because it changes parameters of eel growth in the basal-most region of the leaf, the sheath, resulting in dramatically altere d sheath morphology. The strongly expressive allele Gn1-R also gives rise t o a floral phenotype in which ectopic carpels form. Introgression studies s howed that the severity of the Gn1-conferred phenotype is strongly influenc ed by genetic background. Gn1 maps to knox4, and knox4 is ectopically expre ssed in plants with the Gn1-conferred phenotype. Immunolocalization experim ents showed that the KNOX protein accumulates at the base of Gn1 leaves in a pattern that is spatially and temporally correlated with appearance of th e mutant phenotype. We further demonstrate that Gn1 is knox4 by correlating loss of the mutant phenotype with insertion of a Mutator transposon into k nox4.