The objective of the proposed research is to use a molecular genetic approach to gain an understanding of the developmental mechanisms that regulate cell expansion in tip-growing plant cells. To achieve this goal, Dr. Schiefelbein has chosen to study elongation in root hairs, a relatively simple and accessible cell type in plants. Mutants of Arabidopsis thaliana have been isolated that synthesize root hairs with irregular growth patterns. He will initially concentrate on two mutants (rhd3 and rhd4) that, based on preliminary analyses, are likely to harbor mutations in genes intimately involved in root hair elongation. The specific research approaches will include: 1) characterization of the ultrastructure, microfilaments, and ion currents in the wild type and mutant root hairs, 2) linkage analysis and isolation of new alleles of the RHD3 and RHD4 genes, 3) RFLP mapping and molecular cloning of the genes by chromosome walking with a yeast artificial chromosome library, and 4) isolation and stepwise characterization of additional genes affecting root hair elongation. The results from this research are expected to provide basic information on the mechanism regulating expansion in tip-growing cells, as well as to define specific genes governing root hair elongation in plants.
