Award Date

1-1-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

First Committee Member

Jeffery Qingxi Shen

Number of Pages

186

Abstract

The goal of my research is to understand the molecular mechanism by which hormones control seed germination. Gibberellins (GA) promote, while abscisic acid (ABA) and salicylic acid (SA) inhibit seed germination. Key molecules in these signaling pathways include receptors, secondary messengers, protein kinases and phosphatases, and transcription factors. My study focuses on how WRKY transcription factors modulate the expression of an alpha-amylase gene (Amy32b), which is up-regulated by GA, but down-regulated by ABA and SA in the aleurone cells of germinating seeds; Chapter 2 started with the annotation and phylogenetic analyses of the WRKY gene superfamily, followed by functional studies of WRKY proteins in mediating ABA responses. Eighty-one WRKY genes were identified in the rice genome through computational analyses. Phylogenetic analyses based on WRKY domain sequences suggest that extensive duplications and losses of the WRKY domain occurred during evolution of this gene family. Transient expression studies suggest that among four WRKY genes that are ABA-inducible in aleurone cells, OsWRKY72 and OsWRKY77 function as transcription activators while OsWRKY24 and OsWRKY45 are repressors of the ABA-inducible HVA22 gene; Chapter 3 presents cellular and biochemical data to support a novel model that two transcription repressors OsWRKY51 and OsWRKY71 mediate the crosstalk of GA and ABA signaling. Both genes are ABA-inducible, but GA-repressible in the embryos and aleurone cells of germinating rice seeds. The interaction of OsWRKY51 and OsWRKY71 synergistically represses the GA-induced Amy32b expression, likely by functionally interfering with the GA-inducible transactivator, GAMYB; The mechanism underlying the crosstalk of SA, ABA and GA is reported in Chapter 4. Similar to ABA, SA blocks seed germination likely through repressing the expression of alpha-amylase genes such as Amy32b. Over-expression of the SA-inducible and GA repressible HvWRKY38 in aleurone cells blocks GA-induced Amy32b expression. Therefore, HvWRKY38 might mediate the crosstalk of SA, ABA and GA signaling in regulating alpha-amylase expression and seed germination; My research demonstrates the high efficiency of the approach integrating bioinformatics and experimental biology in addressing the cell-biological signaling network. The finding derived from this research helps advance towards achieving our long-term goal: to improve the yield and quality of rice and other cereals.

Keywords

Abscisic Acid; Approach; Bioinformatic; Biology; Cross Talk; Crosstalk; Experimental; Gibberellins; Hormone; Integrating; Mediating; Pathways; Proteins; Roles; Seed Germination; Signaling

Controlled Subject

Molecular biology; Botany; Cellular biology; Bioinformatics

File Format

pdf

File Size

5263.36 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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