Genetic and molecular-biological investigations are proposed in order to determine whether a developmental compartment exists in the maize leaf. Previously, cell-lineage analyses and KNOX (markers of leaf/nonleaf identity) immunolocalizations of maize meristems indicated that a margin domain is not utilized in the leaf founder-cells of narrow sheath mutant plants. At maturity, narrow sheath mutant leaves are extremely narrow and devoid of specific cell and tissue types normally found at the edges of maize leaves. Together, these data indicate that a margin domain exists in the maize leaf and that this plant compartment may be established at the meristematic founder-cell stage via the activity of the duplicate genes narrow sheath1 and narrow sheath2. Three projects are proposed to test whether leaf margin development proceeds via the subdivision of founder-cells into distinct developmental domains or if the leaf margin is patterned much later in a non-compartmentalized manner.
1) Clonal mosaic analysis will be used to infer the developmental timing and tissue-layer specificity of Ns2 gene function. This analysis will also determine if NS2 activity is confined to the margin domain of the leaf or is required in other leaf regions.
2) Complete genomic and cDNA clones corresponding to each of the narrow sheath genes will be isolated and sequenced. Sequence analyses will reveal the degree of structural homology among nsl and ns2, and may suggest their molecular function.
3) Northern analyses, RNA in situ hybridizations and immunohistolocalization assays of Ns gene expression throughout leaf development will test the hypothesis that the margins of maize leaves are patterned during the founder-cell stage of development by the domain-specific expression of the Ns genes.
