Functional and Molecular Analysis of Brick Genes in Maize

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During development, cells acquire a wide variety of shapes that aretailored to their differentiated functions. The shape of a plant cell isdictated by the wall that surrounds it, a complex and highly structuredmatrix of carbohydrates, proteins, phenolic compounds, and lipids. Thepattern in which a wall expands as that cell enlarges depends upon itscomposition and structure, which in turn is controlled by the cell within.The work described in this proposal is aimed at furthering ourunderstanding of mechanisms governing plant cell morphogenesis. Mutations in three maize genes required for leaf epidermal cellmorphogenesis have been isolated. In all of these "brick" mutants,epidermal cells expand to achieve a normal size and overall rectangularshape, but are completely lacking the marginal lobes characteristic of leafblade epidermal cells. Preliminary studies of brk mutant phenotypes haveled to two alternative hypotheses for Brk gene function. The first is thatBrk genes promote intracellular asymmetries, which direct non-uniformpatterns of deposition/secretion of wall components, producing specializedepidermal cell shapes. The second is that Brk genes are required for thesynthesis of particular wall components needed to achieve non-uniformpatterns of cell expansion. In the experiments proposed under Specific Aim1, these hypotheses are explored through further characterization ofintracellular and extracellular events associated with the formation ofepidermal cell lobes, and how these events are altered in each of the 3 brkmutants. Specific Aim 2 is to use genetic mosaic analysis to determinewhether each gene functions cell autonomously or non-autonomously tocontrol cell shape. To pursue an understanding of Brk gene function inmolecular terms, Specific Aim 3 is to clone one of the Brk genes usingtransposon tagging. Subsequent to cloning one of the Brk genes, the aminoacid sequence of its predicted protein product will be determined andanalyzed for homology to other proteins or protein motifs, and theexpression of this gene will be examined to determine how it relates toepidermal cell morphogenesis.