Date of Award

Fall 2002

Project Type

Dissertation

Program or Major

Biochemistry

Degree Name

Doctor of Philosophy

First Advisor

G Eric Schaller

Abstract

The ethylene receptor family of Arabidopsis consists of five members, ETR1, ETR2, ERS1, ERS2, and EIN4. Regulation of ethylene receptor expression in Arabidopsis was studied using three different approaches. First, the effect of ethylene-pathway mutations upon expression of ETR1 was examined. Ethylene-insensitive mutations in ETR1 resulted in a post-transcriptional increase in levels of the mutant receptor. Treatment of seedlings with silver, which leads to ethylene insensitivity, also resulted in an increase in levels of ETR1. Mutations in other components of the ethylene pathway had little effect upon expression of ETR1. Second, microarray analysis was performed using reciprocal mutants to examine ethylene-regulated gene expression. A large subset of ethylene-induced genes were involved in ethylene signal transduction. Among these, the ethylenereceptors ETR2, ERS1, and ERS2 showed pronounced induction, ETR1 displayed limited induction, and EIN4 remained unchanged. Third, the effect of abiotic stress upon expression of ethylene receptors was examined. Microarray analysis indicated that the expression of ETR1, ETR2, and ERS1 was reduced after exposure to salt stress, while expression of ERS2 and EIN4 remained unchanged. Changes in gene expression were reflected at the protein level as levels of the ETR1 protein decreased following salt and osmotic stress. A role for ethylene signal transduction in the plants' response to abiotic stress was confirmed by examining the effect of salt and osmotic stress upon the germination of ethylene pathway mutants. My results demonstrate that changes in expression level of ethylene receptors provide a means by which ethylene signal transduction can be activated or repressed.

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