Genetic and Molecular Analysis of the Dominant Mutations that Define the Kn1 Locus in Zea Mays

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The knotted mutation in maize disrupts normal leaf development by altering the timing of differentiation and growth pattern of certain leaf cells. The phenotype ranges from a clearing of the photosynthetic cells that normally surround the lateral veins, to sporadic knots along the lateral veins which grow out of the plane of the leaf. Lastly, the ligule is displaced and found parallel to the veins in the leaf blade. There are four Kn1 mutations that differ in their severity and timing although they all map to the same location on the long arm of chromosome 1. We have cloned one of the mutations using Ds2 as a transposon tag. This particular mutation requires a trans-acting Ac for expression and the phenotype increases in severity with an increase in Ac dosage. The Ds2 mutation, Kn1-2F11, has enabled us to begin a molecular analysis of another Kn1 mutation, Kn1-0. Kn1-0 appears to be a duplication, the breakpoint of which falls within 1 kb of the site of the Ds2 insertion in Kn1-2F11. DNA 5 kb distal to the region altered in these two mutants is highly conserved. We will isolate and analyze cDNA and genomic clones of the different knotted mutations and their wildtype alleles. In situ hybridization techniques will be used to determine when and in what tissues the Kn1 and wildtype genes are expressed. The nature of the Ds-Ac interaction in the Kn1-2F11 mutation will be determined. Our long range goal is to determine how the development of the leaf involves Kn1 or "kn" expression. The use of recombinant technology has made it possible to study plant development at a molecular genetic level. However, as yet, only a few laboratories have started doing so. Corn, because it has been genetically studied extensively, is an excellent experimental organism. The results of this study should provide greater insight into how plants form leaves.