Molecular characterization of soybean resistance to soybean cyst nematode

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Title from PDF of title page (University of Missouri--Columbia, viewed on January 27, 2011).Thesis advisor: Dr. Melissa G. Mitchum.Vita.Ph. D. University of Missouri--Columbia 2009.The soybean cyst nematode, Heterodera glycines, is a devastating pathogen to soybean worldwide. This obligate parasite establishes specialized feeding cells within host roots that are required for completion of the nematode life cycle. In resistant soybean plants, juveniles penetrate into roots, but subsequent degeneration of feeding cells prevents the nematode from further growth and development. The soybean resistance genes and signaling pathways controlling this process have not yet been identified. The Rhg4 locus, a major QTL controlling soybean resistance against H. glycines was previously sequenced and patented by two independent research groups and a gene encoding a leucine-rich repeat receptor-like kinase protein (LRR-RLK) was proposed as the gene for resistance. These claims, which have been generally accepted by the soybean community, were never validated by functional studies to confirm that this was the correct gene for resistance. In this study, a combination of approaches including TILLING, haplotyping, and complementation were not able to confirm a role for this gene in resistance to H. glycines. Consequently, further fine mapping and testing of additional candidate genes is underway. In addition, the role of salicylic acid (SA), a key signaling molecule in plant resistance to biotrophic pathogens was investigated for a role in Rhg4-mediated resistance to H. glycines. Studies measuring endogenous SA levels in response to nematode infection and parasitic success on transgenic plants compromised for SA production or on soybean roots following exogenous application with SA, suggest that SA plays a role in basal resistance, but may not play a major role in R gene-mediated resistance to H. glycines.Includes bibliographical reference

Characterizing the role of Glycine max NHL gene family members in plant-nematode interactions [abstract]

Abstract only availableSoybean cyst nematode (SCN; Heterodera glycines) is a microscopic parasitic roundworm of soybean that causes nearly $1 billion dollars in annual yield loss in the United States. SCN damages the plant by attaching itself to the soybean root system, where it forms a complex feeding site and drains vital nutrients from the plant. Naturally resistant soybean lines have been used as the primary strategy to manage SCN, because they have evolved a natural mechanism for resisting SCN infection. However, soybean resistance against SCN is derived from a small genetic base and repeated annual plantings of these same resistant lines has selected for populations of SCN that can reproduce on the resistant lines. Therefore, understanding the molecular mechanisms of how some soybean plants have the ability to naturally resist infection by SCN is critical for designing new strategies to improve crop plant resistance to SCN. My project focuses on soybean NDR1/HIN1-like (NHL) genes found to be expressed at higher levels specifically within SCN-induced feeding cells of resistant soybean as compared to susceptible soybean. To gain insight into the potential role of these genes in soybeans ability to resist SCN, full-length gene and cDNA sequences have been isolated using techniques known as genome walking and RACE PCR. RNAi and overexpression constructs have been generated to directly test the function of these genes in SCN resistance. To gain insight into the nematode-responsive regulation of each gene, the endogenous promoter sequences have been isolated and fused to the _-glucuronidase reporter gene for expression studies. This project will give insight into the mechanisms the soybean plant uses to defend itself against SCN infection and hopefully reveal crucial results which aid in the goal of developing SCN resistant soybean.Life Sciences Undergraduate Research Opportunity Progra