Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Williams, W. Paul

Committee Member

Luthe, S. Dawn

Committee Member

Ma, Din-Pow

Committee Member

Li, Jiaxu

Committee Member

Willard, Scott

Date of Degree

5-1-2010

Document Type

Dissertation - Open Access

Major

Molecular Biology

Degree Name

Doctor of Philosophy

College

College of Agriculture and Life Sciences

Department

Department of Biochemistry and Molecular Biology

Abstract

Maize is an important food crop in most parts of the world including the United States. The plants growing in the field are constantly challenged with various biotic stresses like insect herbivores and fungal pathogens. The physical wounds produced on the growing crops by the insects render the plants more vulnerable to the fungal pathogens. Hence developing both insect and fungal resistant maize varieties is crucial to benefit more from the harvest. Several studies have been in advance in this direction and as a consequence insect, in particular lepidopteran larve resistant maize genotype Mp708 and Aspergillus flavus resistant genotype Mp313E were developed. This study particularly focuses on understanding the functional involvement of the major phytohormones in the signal transduction and expression of the unique defense protein, Maize insect resistance 1-cysteine protease (Mir1-CP) shown to accumulate in response to herbivory by lepidopteran larvae, Spodoptera frugiperda (Fall armyworm, FAW) as a defense mechanism. Using a pharmacological approach involving exogenous hormone and hormone inhibitor treatments and analyzing the expression and accumulation of Mir1-CP protein and mir1 transcript by immunoblot and qRT-PCR analysis respectively, both JA and ET were found to be involved in mediating Mir1-CP accumulation with JA acting upstream of ET. Results also indicate that Mir1-CP accumulation involves both transcriptional and post-transcriptional (or post-translational) regulations. A different part of the study involved in understanding and evaluating the performance of Aspergillus flavus on the resistant and susceptible maize genotypes during infection. As of part of this study I also analyzed and compared the defense response offered by the resistant maize genotype, Mp313E and the susceptible genotype, Va35 by looking at the expression levels of the various defense related genes. The potency of the resistant maize genotype in sustaining the fungal infection in the field was of particular focus. Resistant maize genotype Mp313E was found to potentially oppose A.flavus proliferation and colonization and also delay aflatoxin biosynthesis unlike Va35. The up regulation of the maize defense genes during the early time points of infection, in Mp313E, indicate the potential role of these genes in conferring resistance against fungal pathogens.

URI

https://hdl.handle.net/11668/14973

Comments

fungal resistance||jasmonate||ethylene||insect resistance||maize||post translational regulation||Post trascriptional regulation||Mir1

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