Regulated expression of a soybean β-expansin gene
Abstract
In the present study, the hypothesis that elaborate hormone-regulated gene expression presides over changes in the size and shape of plant cells, and ultimately plants, is examined. Cim1 from soybean has two characteristics that make it an ideal gene for the analysis of this question. Cim1 is a known hormone-regulated gene (Cytokinin-induced mRNA), and the Cim1 protein product is predicted to be a β-expansin. Expansins have potent cell wall loosening capabilities that modulate the growth restraining forces of the plant cell wall. Thus, Cim1 is used here as a model gene to study the steps intermediate to hormone application and cell wall loosening, a direct physical outcome that impacts plant development. A number of regulatory points were discovered. In particular, the data suggest that protein phosphatase activity is required for the cytokinin-induced stability and subsequent accumulation of Cim1 mRNA in soybean cells. The data also indicate that the hormones cytokinin and auxin act synergistically to induce the accumulation and proteolytic processing of the Cim1 protein product and that other posttranslational modifications, such as N-linked glycosylation, proline hydroxylation, and proteolysis also contribute to the maturation and final degradation of the Cim1 expansin. These data provide the most detailed description currently available for the intermediate expression products of a single expansin gene. The plant cell wall largely determines the strength and texture of plant-derived products (i.e. lumber, paper, cotton and fruit), and biotechnologists are interested in altering expansin gene expression to improve output quality from these major industries. This study predicts that multiple control points, perhaps influenced by multiple plant hormones, are likely to be relevant to the expression of a given expansin gene. Determining the rate-limiting step will be an issue for achieving meaningful over-expression, while the regulated steps described otter potential targets for altering expression. Most importantly, this work contributes to our knowledge of chemical plant growth regulators and the signals that they employ to direct the growth and development of plants.
Degree
Ph.D.
Advisors
Crowell, Purdue University.
Subject Area
Botany
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.