Theses and Dissertations

Issuing Body

Mississippi State University


Lawrence, Gary W.

Committee Member

Klink, Vincent

Committee Member

Lu, Shien

Committee Member

Li, Jiaxu

Committee Member

Lawrence, Kathy S.

Date of Degree


Document Type

Dissertation - Open Access


Agriculture and Life Sciences

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology


The understanding of plant defense response in plant-pathogen interaction provides useful information to combat the disease. Soybean cyst nematode (SCN), Heterodera glycines, and charcoal rot causing fungus, Macrophomina phaseolina, are major pathogens of soybean, Glycine max, and infestation with SCN has found to aggravate the fungal disease severity. The gene expression analysis in resistant and susceptible interactions between H. glycines and G. max has identified some candidate resistance genes and signaling pathways but they are yet to be fully characterized. This dissertation aims to characterize one such gene, Conserved Oligomeric Golgi (COG) complex. The COG complex is important in structural and functional integrity of Golgi complex among eukaryotes, but very little is understood about its role in plants. This study demonstrated a defensive role of the COG complex in G. max against H. glycines. The transgenic plants for overexpression of COG genes, which were originally susceptible to the pathogen, showed reduced parasitism. In contrast, the RNA interference (RNAi) in originally resistant soybean lines showed a marked increase in parasitism. Further, these COG genes were found to be inducible by harpin elicitor molecules. In another study, the already proven resistance genes (NDR1, NPR1, EDS1 and TGA2) against H. glycines were investigated against the fungal pathogen. The transgenic plants for overexpression of these genes showed reduced disease severity, while the RNAi resulted increased severity compared to control lines. In addition, the H. glycines parasitism study and the candidate gene expression analysis in M. Phaseolina susceptible and moderately resistant G. max indicate that there are some cross communications between the defense processes of G. max to H. glycines and M. phaseolina.



harpin||COG complex||Glycine max||Heterodera glycines||Defense response