During development, cells acquire a wide variety of shapes that are >tailored to their differentiated functions. The shape of a plant cell is >dictated by the wall that surrounds it, a complex and highly structured >matrix of carbohydrates, proteins, phenolic compounds, and lipids. The >pattern in which a wall expands as that cell enlarges depends upon its >composition and structure, which in turn is controlled by the cell within. >The work described in this proposal is aimed at furthering our >understanding of mechanisms governing plant cell morphogenesis. > Mutations in three maize genes required for leaf epidermal cell >morphogenesis have been isolated. In all of these "brick" mutants, >epidermal cells expand to achieve a normal size and overall rectangular >shape, but are completely lacking the marginal lobes characteristic of leaf >blade epidermal cells. Preliminary studies of brk mutant phenotypes have >led to two alternative hypotheses for Brk gene function. The first is that >Brk genes promote intracellular asymmetries, which direct non-uniform >patterns of deposition/secretion of wall components, producing specialized >epidermal cell shapes. The second is that Brk genes are required for the >synthesis of particular wall components needed to achieve non-uniform >patterns of cell expansion. In the experiments proposed under Specific Aim >1, these hypotheses are explored through further characterization of >intracellular and extracellular events associated with the formation of >epidermal cell lobes, and how these events are altered in each of the 3 brk >mutants. Specific Aim 2 is to use genetic mosaic analysis to determine >whether each gene functions cell autonomously or non-autonomously to >control cell shape. To pursue an understanding of Brk gene function in >molecular terms, Specific Aim 3 is to clone one of the Brk genes using >transposon tagging. Subsequent to cloning one of the Brk genes, the amino >acid sequence of its predicted protein product will be determined and >analyzed for homology to other proteins or protein motifs, and the >expression of this gene will be examined to determine how it relates to >epidermal cell morphogenesis.
