Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Sangeeta Dhaubhadel

2nd Supervisor

Susanne Kohalmi

Abstract

Soybean’s yield is threatened by Phytophthora sojae, a pathogen responsible for stem and root rot disease. Glyceollins, unique antimicrobial agents specific to soybeans in partially preventing P. sojae infection, are derived from the isoflavonoid branch of the general phenylpropanoid pathway. One pivotal enzyme exclusively involved in glyceollin synthesis in soybean is the isoflavone reductase (GmIFR), which catalyzes the 2'-hydroxydaidzein conversion to 2'-hydroxy-2,3-dihydrodaidzein as a precursor for glyceollin biosynthesis. To comprehensively identify all members of the GmIFR gene family within the soybean genome, keyword and blast protein searches were conducted, identifying 98 putative GmIFRs. Among these candidates, seven GmIFR candidates were selected for further investigation of which six were confirmed to be localized to the cytoplasm. Additionally, GmIFR candidates exhibited soluble expressions and were successfully purified. These findings provide a fundamental knowledge of GmIFR family members and their functional characterizations in the glyceollin pathway in soybean.

Summary for Lay Audience

As the global population is continuously growing, there is a steady rise in the demand for food resources. Nowadays, environmental conservation, greenhouse gas emissions reduction, and preservation of natural resources such as water and land direct people towards consuming plant-based foods and products. Soybean, with its high protein and oil content, is a globally important agricultural valuable source of both human and animal nutrition, human health, and industrial products. However, various stresses, particularly pathogens like Phytophthora sojae, severely impact soybean cultivation, leading to substantial annual losses in crop yield. To address this issue, breeders have developed multiple strategies including soil tillage, seed treatments with fungicides, and crop rotation with non host plant-pathogen. However, these approaches prove somewhat less effective due to the pathogen's long-term survival in soil for more than ten years. At the molecular level, glyceollin pathway in soybean is involved in response to various stress including disease, nutritional limitations, drought, and flooding, by creating a defense mechanism involving many enzymes such as isoflavone reductase. So, it is critical to determine all isoflavone reductase members which play key roles in glyceollin defense pathway in response to P. sojae infection.

In the current study, by comprehensive identification of all members of the isoflavone reductase gene family within the soybean genome, I found seven candidates which are clustered with identified isoflavone reductase in other legumes plants. Analysis of datasets unveiled that GmIFR candidates possess three conserved motifs, exhibit transcript expression in infected soybean tissues, and high expression levels in the root. By analyzing functional characterization of GmIFR proteins, I discovered that GmIFRs in glyceollin pathway are localized in cytoplasm, and they are also expressed in soluble form.

Knowing GmIFR family members and its functional characterizations will provide a fundamental knowledge of this family in the glyceollin pathway and help to develop a more profound understanding of soybean's natural resistance against P. sojae infection, resulting in increased glyceollin production, and save millions of dollars of annual soybean losses globally.

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