Degree Type

Dissertation

Date of Award

2018

Degree Name

Doctor of Philosophy

Department

Agronomy

Major

Genetics

First Advisor

Madan K. Bhattacharyya

Abstract

Soybean is an important source of protein and oil for both human and animal nutrition. The United States is the world’s leading soybean producing nation. In 2016, the U.S. soybean production was valued over 40.9 billion dollars. Sudden death syndrome (SDS) of soybean is ranked as one of the top ten yield limiting disease of soybean and is caused by the pathogen Fusarium virguliforme. Fusarium virguliforme is a soil borne fungal pathogen, which infects soybean roots resulting in both root sot symptoms and foliar chlorosis and necrosis. To date there is no known single gene resistance to SDS, the resistance that has been found is complex and heavily influenced by the environment. To gain a better understanding of the role of fungal genes in SDS development, RNA-sequencing of F. virguliforme infected soybean roots was conducted. Many F. virguliforme genes involved in cell wall degradation as well as phytoalexin detoxification were up-regulated during infection. Interestingly, the fungus also increases expression of a fungal polyamine oxidase gene FvPO1. Little is known about the role of fungal polyamine oxidases. Therefore, knockout mutants and complimented mutants for FvPO1 gene were created. Mutant studies confirmed the FvPO1 enzymes polyamine oxidase activity. The Δfvpo1 mutant did not have altered growth, sporulation or soybean infection phenotypes. Transgenic soybean plants expressing FvPO1 did not have altered defense response to either infection with F. virguliforme or to infection with the bacterial pathogen Pseudomonas syringae pv glycinea. Comparisons of the transcriptomes of soybeans inoculated with Δfvpo1 and the complimented Δfvpo1::FvPO1 mutant showed that the presence of FvPO1 does not alter the expression of soybean genes following F. virguliforme infection. Interestingly, three fungal genes related to the metabolism of the secondary metabolite phenylacetic acid were upregulated in the Δfvpo1 mutant fungus during infection. Phenylacetic acid has been suggested to play a role in induced systemic resistance in plants. When F. virguliforme was grown on media containing phenylacetic acid fungal growth was reduced. Δfvpo1 mutants do not have altered growth phenotype when compared to the wild type on the phenylacetic acid media. FvPO1 has increased expression during F. virguliforme infection of soybean roots but is not necessary for F. virguliforme to infect soybean or cause typical symptoms. FvPO1 is increased with addition of the polyamines spermine and spermidine to the media. Therefore, the increased expression of FvPO1 following infection may be due to the presence of plant polyamines and the pathogen may use plant polyamines as an additional nutrient source during infection. Based on transcriptomics study, FvPO1 expression appears to regulate the phenylacetic acid metabolism pathway.

Copyright Owner

Jordan Lillian Baumbach

Language

en

File Format

application/pdf

File Size

168 pages

Included in

Genetics Commons

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