Award Date

12-1-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

First Committee Member

Jeffery Q. Shen

Second Committee Member

Stanley D. Smith

Third Committee Member

Andrew J. Andres

Fourth Committee Member

Paul J. Schulte

Fifth Committee Member

Ernesto Abel Santos

Number of Pages

165

Abstract

The goal of my research is to understand the molecular mechanism by which hormones control seed germination and response to abiotic stresses, in order to reduce yield loss in rice via the development of biotech applications. Abscisic acid (ABA) inhibits, while gibberellins (GA) promote, seed germination. In addition, ABA plays a critical role in stress responses, such as the regulation of seed germination under salt and salinity stresses. Key components in these signaling pathways include receptors, secondary messengers, protein kinases and phosphatases, and transcription factors. My study focused on how WRKY transcription factors modulate ABA and GA signaling, therefore affecting seed germination and responses to abiotic stresses.

Chapter 2 begins with the identification of OsWRKY53 and -70, close homologs to OsWRKY24, followed by functional studies of these WRKY proteins in mediating ABA and GA response. The roles of these proteins as transcription factors are indicated by their localization in the nucleus, ability to bind to the W-box in promoters, and the transactivation activity of all three. Transient expression analyses indicated that all three antagonize the GA and ABA signaling pathways in a dosage-dependent manner. When the three transcription factors were paired, they acted additively in the antagonism of both ABA and GA signaling. A combination of all three led to additive antagonism of ABA signaling, but synergistic antagonism of GA signaling. These data suggest that OsWRKY24, -53, and -70 may function in a partially redundant manner to antagonize the ABA and GA signaling pathways.

Chapter 3 presents a functional study of OsWRKY70 in regulating seed germination and response to abiotic stresses. Overexpression lines of OsWRKY70 were successfully generated using Agrobacterium-mediated rice transformation. Studies of the knockout mutant and overexpression lines demonstrated that OsWRKY70 negatively regulates seed germination when nutrients are insufficient. In addition, mutation of OsWRKY70 in rice increased drought and salinity tolerance, which further suggests a negative role of OsWRKY70 in the regulation of abiotic stress responses.

Chapter 4 illustrates the interaction between an NHL protein, OsNHL2, and two WRKY transcription factors, OsWRKY53 and -70. As with OsWRKY53 and -70, OsNHL2 also negatively regulates the ABA and GA signaling pathways. Furthermore, paired with each of these WRKY transcription factors, the WRKY and NHL proteins functioned additively to repress the ABA-induced HVA22 promoter, but antagonistically to repress the GA-induced Amy32b promoter. These data suggest a cooperative role between the WRKY transcription factors and OsNHL2 in the regulation of ABA, but not GA, signaling.

My research demonstrates the roles of WRKY transcription factors, in cooperation with an NHL intermembrane protein, in the regulation of seed germination and responses to abiotic stresses. My finding that oswrky70 mutant has fast and uniform germination and better seedling establishment under abiotic stress will save great effort, time, and expense used in seed priming in the field. This research opens up new perspectives for the design of molecular strategies to obtain good crop establishment and finally improve the crop yield.

Disciplines

Molecular Biology | Plant Sciences

Language

English

Available for download on Thursday, December 31, 2020


Share

COinS