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Degree

Doctor of Philosophy, Ohio State University, Horticulture and Crop Science, 2004.

Abstract

While sugars are important signaling molecules for the control of plant growth and development, little is known about the molecular mechanisms underlying sugar sensing and signal transduction in plants. To date, many glucose insensitive mutants have been found to be alleles of abscisic acid (ABA) biosynthetic or perception mutants. On the basis of the information on the previous mutant screens, steady-state mRNA analysis, and global transcription profiling, I hypothesized that sugar signals might be transmitted through an ABA-independent signal transduction pathway. I have established a mutant screen system using marker genes that are very sensitive to glucose. Asparagine synthetase1 (ASN1) is completely repressed by low levels of exogenous glucose in less than 3 h. Glucose repression of ASN1 also involves protein phosphorylation but not de novo protein synthesis. In addition, hexokinase appears to be required for the glucose repression of ASN1. Most critically, ASN1 repression by glucose is not affected by ABA under the conditions tested. Homozygous transgenic plants containing the ASN1 promoter fused with luciferase or green fluorescent protein genes have been generated. Significant quantities of ethyl methane sulphonate mutagenized M2 seeds from three selected lines were obtained. A large-scale mutant screen has been carried out using a luminescence-imaging system. Phenotypic and molecular characterization of putative mutants is expected to reveal signaling mechanisms involved in the regulation of ASN1 expression by sugar. The role of ACT (Aspartokinase, Chorismate mutase, and prephenate dehydrogenases (TyrA)) domain-containing genes is largely unknown. Functional characterization has been accomplished to determine the sugar response and gene expression of ACTPK. The ACTPK3 transcript was completely abolished by low levels of exogenous glucose in 3 h. The steady-state mRNA analysis results showed that ACTPK3 is likely controlled by the circadian clock that is epistatic of sugar response. The glucose repression of ACTPK3 required sugar transport, sugar phosphorylation, hexokinase, de novo protein synthesis, and protein dephosphorylation. Furthermore, the ACTPK3 repression by glucose was not modulated by ABA. Several T-DNA knockout lines have been obtained and results of initial phenotypic analysis suggested that ACTPK might be involved in plant sugar response.

Subject Headings

Biology, Molecular

Keywords

Arabidopsis; sugar signal transduction pathway

Advisor

Jyan-Chyun JANG

Pages

xxiv, 173p.

Document number: osu1092842961
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1092842961

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