Current Research In the Smith Laboratory

The functions of leaves, like other multicellular plant organs, depend on the coordinated development of many different cell types, which form in characteristic patterns. Our research is concerned with processes underlying the formation of cell patterns during plant development: the control of cell division orientations, the spatial regulation of cell expansion, and the patterning of cellular differentiation. 

We are taking a multidisciplinary approach to investigate these processes in the context of maize leaf development. The cellular pattern of the maize leaf epidermis is extremely regular; mutations altering this pattern in various ways allow us to identify genes required for the spatial regulation of cell division, expansion and differentiation. Tools of cell and molecular biology are used to further our understanding of the functions of genes identified by these mutations. For example, the tangled1 mutation causes leaf cells to divide in aberrent orientations and leads to widespread abnormalities in the shape and arrangement of epidermal cells. We have found that this gene is required for the proper positioning of cytoskeletal arrays involved in the formation and placement of new cell walls, is expressed specifically in dividing cells, and encodes a protein related to the basic domain of APC (adenomatous polyposis coli protein). Similarly, discordia1 and discordia2 genes are also required for proper orientation of leaf cell divisions, but only the asymmetric cell divisions involved in the formation of stomatal complexes and silica-cork cell pairs.Three brick genes are required for normal morphogenesis of non-specialized epidermal cells: in brick mutants, cell margins are straight instead of wavy. Many other mutations have also been isolated affecting various aspects of leaf epidermal cell pattern. Future work will concentrate on developing our understanding of the functions of these genes through analysis of mutant phenotypes coupled with molecular analysis of the corresponding gene products.