Doctor of Philosophy (PhD)


Biological Sciences

Document Type



Arabidopsis thaliana is a model organism used for genetic, molecular, and biochemical analyses of higher plant processes. Leaf hairs (trichomes) on the surface of Arabidopsis leaves are macroscopic single cells that develop by elaborate cell expansion and differentiation of the epidermis. Arabidopsis trichomes provide an excellent model to study plant cell expansion and differentiation and the cell cycle. Upon maturation, an Arabidopsis trichome becomes a branched, stellate structure with a highly birefringent cell wall. Arabidopsis mutants have been isolated that have trichomes that look glassy and have reduced birefringence. CONSTITUTIVE PATHOGEN RESISTANCE5 (CPR5) is a previously isolated Arabidopsis gene observed to have trichomes with reduced branching. Work presented here shows cpr5 trichomes to have reduced birefringenceand leaves to have less paracrystalline cellulose. The leaves, stems, and roots of cpr5 plants have defects in cell expansion. The cells of cpr5 leaves prematurely stop expanding, resulting in leaves that are much smaller than wild-type leaves. Stem and root cells of cpr5 plants have reduced polar expansion, resulting in longitudinally shorter cells. The roots of cpr5 plants grow at a slower rate than wild-type roots. In trichome development, CPR5 acts downstream of genes involved in trichome initiation. Synthetic genetic interactions between CPR5, TRIPTYCHON, and NOECK (NOK) suggest these three genes might interact to control trichome cell expansion. An allele of NOK was isolated in a screen of cpr5-2 phenotypic modifiers. Trichomes on nok plants are extrabranched, glassy, and have reduced birefringence. NOK maps to the top of chromosome three. Additionally, a novel 4-branched trichome mutant was identified in the modifier screen and would be classified as an asymetric branch mutant. This mutation maps to the top of chromosome one. In a separate screen, a novel glassy trichome mutant called DEFLATED TRICHOMES (DFT) was isolated because the trichomes had collapsed cell walls. Trichomes on dfl plants also have reduced birefringence. DFT maps to the top of chromosome five. Further characterization of NOK and DFT is integral to understanding the degree to which the glassy trichome phenotype is indicative of the nature of the protein.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

John C. Larkin