Analysis of genetic mosaics shows that the extra epidermal cell divisions in Knotted mutant maize plants are induced by adjacent mesophyll cells

Abstract

The technique of ‘fate-mapping’ or ‘mosaic mapping’ takes advantage of genetically marked progenitor cells that confer a phenotypic difference in order to determine the cells' contribution to the final organism. Pioneered by the gynandromorph studies of Sturtevant¹, this technique has been used extensively to understand Drosophila development². For certain plant species, naturally occurring chloroplast mosaics have been used to follow cell lineages³. In other plant species, mosaics can be generated by using X-ray-induced somatic mutations^4,5. Here we have used X rays to create genetic sectors in maize that are lacking a mutation which alters leaf development—Knotted or Kn. From the sectors observed, we determined that the genotype of the mesophyll (internal cell layers) and not the genotype of the epidermis (outer layer) was critical for Kn expression, and that the mesophyll induced the epidermis to divide.