Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/24/2004
Publication Date: 2/25/2005
Citation: Lambert, K.N., Bekal, S., Domier, L.L., Niblack, T.L., Noel, G.R., Smyth, C.A. 2005. Selection of heterodera glycines chorismate mutase-1 on nematode resistant soybean. Molecular Plant-Microbe Interactions. 18:593-601. Interpretive Summary: The soybean cyst nematode (SCN) is the most destructive pathogen of soybean in the United States. Genetic diversity in the parasitic ability of SCN allows it to reproduce on SCN resistant soybean. The SCN enzyme chorismate mutase 1 (Hg-CM-1) is secreted by SCN infective juveniles into soybean roots and has the potential to suppress host plant defense compounds. Inbred SCN lines were developed to study the genetics of Hg-CM-1 and its relationship to SCN pathogenicity. Several forms of HG-CM-1 occur, but two forms, Hg-CM-1A and Hg-CM-1B, were studied in detail. The Hg-CM-1A enzyme was found to be most important. It was the dominant form associated with the ability of SCN to overcome resistance and thereby to allow reproduction of SCN on PI88788 resistant soybean, which is the primary source of resistance in the U.S. used to develop varieties with SCN resistance. This research provides important insight into the mechanisms of nematode parasitism and is the first to describe the molecular basis of how SCN overcomes resistance in soybean. This knowledge will provide the basis for developing and deploying resistant soybeans that have higher levels of resistance to combat SCN.
Technical Abstract: The soybean cyst nematode (SCN), Heterodera glycines is the most destructive pathogen of soybean in the United States. Diversity in the parasitic ability (virulence) of the nematode allows it to reproduce on SCN resistant soybean. Heterodera glycines chorismate mutase-1 (Hg-CM-1) is a nematode enzyme with the potential to suppress host plant defense compounds; therefore, it is considered a candidate virulence protein. Hg-cm-1 is a member of a gene family where two alleles, Hg-cm-1A and Hg-cm-1B have been identified. SCN inbred lines were crossed to ultimately generate an F2 population of second-stage juveniles (J2s) SCN segregating for Hg-cm-1A and Hg-cm-1B. Analysis of the Hg-cm-1 gene copy number revealed that there are multiple copies of Hg-cm-1 alleles in the SCN genome. Segregation of Hg-cm-1A and 1B approximated a 1:2:1 ratio; which indicates Hg-cm-1 is organized as a tandem array of genes that segregate as a single locus. The F2 SCN J2 populations were used to infect resistant (PI88788, PI90763, Hartwig) and susceptible (Lee 74) soybeans. The SCN growing on PI88788 contained predominately Hg-cm-1A allele as result of a statistically significant drop of Hg-cm-1B in the population. This result indicates the Hg-cm-1 gene family functions as quantitative virulence genes or is linked to genes controlling SCN virulence.