9318447 Rivin Dr. Rivin has isolated a maize mutant, termed, dks8 (defective kernel shootless-Mu8), that disrupts the early establishment of a functional shoot meristem, but does not perturb the normal morphogenesis and differentiation of the cotyledon and primary root. These features are unique among the embryo mutants of maize, and they indicate that the gene identified by the dks8 mutation is required for a fundamental step in the formation of the embryonic shoot. By examining the role of this gene during embryonic development, determining if it plays part in post-embryonic development, and identifying its sequence and product, one of the cellular processes critical to plant development may be defined. The research program has the following objectives: 1) Identify other alleles of dks8 from existing mutant collections and by targeted mutagenesis using EMS- mutagenized and Mutator transposon stocks. 2) Clone and map the Dks8 gene using the Mutator transposon tag. The dks8 mutation appears to have been caused by the insertion of a Mu8 element of the Robertson's Mutator transposable system. The sequences flanking this element will be cloned and used to map the dks8 locus. They will be analyzed to discover the product of this developmentally important gene. 3) Determine how and when the dks8 mutation prevents embryonic shoot development. Histological and molecular criteria will be used to test whether the shoot apical meristem cell population is initiated and maintained in the first stages of embryogenesis in dks8 mutants. Somatic embryogenesis and manipulation of endosperm genotype will be used to examine whether dks8 gene action is intrinsic to the developing embryo or whether it acts as part of the larger ovule or seed environment. 4) Determine it the Dks8 gene product is required outside of embryogenesis for the specification or function of the shoot apical meristem. Clonal analysis of cell lineage will be used to determine the effect of the dks8 genotyp e on the developmental fate of cells in an established shoot apical meristem. ***
