Major interests: Compound leaf morphogenesis in dicots; the role of homeobox genes in leaf organization in tomato; evolutionary origins of developmental mechanisms; analysis of maize mutations defective in epidermal organization and cell wall biosynthesis.

Tomato has an unipinnately compound leaf. Several mutations exist that can either reduce or increase the complexity of this leaf. We have used these mutations to propose a model for tomato leaf morphogenesis. Our analyses indicate that the tomato leaf has a distal and proximal domain and that the leaf is specified by a sequential expression of genes in the early primordium. We are using genetic and molecular approaches to identify the genes involved in laying down these domains and leading to the formation of the normal leaf. We have identified a homeobox containing clone, T6, in tomato by homology to the maize homeobox gene Kn1. T6 underproducing plants have very simple leaves and no laminar expansion. In addition another homeobox clone, T12, is also being analyzed by us and appears to play a role in setting up the proximal distal leaf boundary. Analysis of these leaf mutations and cloned genes will help us understand the nature of the compound leaf and the processes leading to its morphogenesis.

Our laboratory is also studying epidermal mutants in corn. We have several transposon tagged alleles of a mutation in corn, adherent1 (ad1), that leads to epidermal fusions. We have shown that the epidermal fusion is a post-genital event and callose (a wound-inducible cell wall polysaccharide) is produced by mutant plants. In addition, several other epidermal mutations that either alter cuticular wax deposition or cause aberrant cell divisions in the epidermis are being analyzed. Our current working hypothesis is that epidermal cells need an intact outer wall to maintain their integrity. When the outer layers are defective either fusions or extra cell divisions occur in this layer. We are analyzing the known epidermal mutants for wall abnormalities and testing for interactions between the mutations. We anticipate that these studies will provide new insights into the structure and function of the plant epidermis.