Title page for ETD etd-11032008-095555

Type of Document Dissertation
Author Kasili, Remmy Wekesa
Author's Email Address kasilirw@mail.nih.gov
URN etd-11032008-095555
Title Isolation and Characterization of Two siamese Phenotypic Modifiers and Their Role in Endoreplication and Trichome Development
Degree Doctor of Philosophy (Ph.D.)
Department Biological Sciences
Advisory Committee
Advisor Name Title
Larkin, John C Committee Chair
Blackwell, Meredith M Committee Member
Moore, Thomas S Jr Committee Member
Moroney, James V Committee Member
Schiebout, Judith A Dean's Representative
  • ENS1
  • cell cycle
  • endoreplication
  • trichome
  • ENS2
  • Arabidopsis
Date of Defense 2008-10-13
Availability unrestricted
Recessive mutations in the ENS1 gene of Arabidopsis thaliana result in reduced trichome branching without altering the ploidy level of trichomes. This implies that ENS1 regulates trichome branching in an endoreplication-independent manner. Mutations in ENS1 also enhance the multicellularity of sim mutant trichomes indicating that ENS1 plays a role in the regulation of the cell cycle during trichome cell differentiation. We have shown that ENS1 is required by the negative regulators of trichome branching for the trichomes to achieve their supernumerary branching. The interaction between ens1-1 and try-JC suggests that ENS1 is involved in both primary and secondary branching events during trichome development.

The ENS1 protein interacts both genetically and physically with the STI protein and double mutant analysis between ens1-1 and sti mutants revealed that they function in the same pathway during trichome development. We propose that ENS1 and STI form a complex that functions to ensure the development of a wild-type trichome phenotype.

The ens2-1 mutations result in trichomes with reduced branching and reduced endoreplication. The ens2-1 mutations also enhance the multicellularity of sim mutant trichomes. The ENS2 gene encodes an activator of the APC/C, a multisubunit protein complex that targets proteins for degradation by the 26S proteasome. Overexpression of ENS2 and its close Arabidopsis homologue AtCCS52A2 results in plants with retarded growth that have enlarged leaf epidermal pavement cells containing highly endoreplicated nuclei. These plants also have large multibranched trichomes with highly endoreplicated nuclei. Both ENS2 and AtCCS52A2 suppress the sim mutant trichome phenotype, suggesting these two genes are functionally similar and function in the same pathway in the regulation of the endoreplication cell cycle.

The ens2-1 mutation induces multicellular trichomes in plants overexpressing cell cycle regulators cyclin B1;1, cyclin B1;2, cyclin D4;1 and CDKA;1, indicating cyclin D4;1 and CDKA;1 may be involved in the regulation of the G2/M as well as the G1/S phase of the cell cycle.

Our research findings indicate that ENS1 and ENS2 are involved in the regulation of the cell cycle during trichome development and that the cell cycle and the cell shape mechanism interact during trichome development to ensure the development of the wild-type trichome architecture.

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