ARS | Publication request: Genomic analysis of soybean resistance to Sclerotinia sclerotiorum

Submitted to: Plant and Animal Genome Conference
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2006
Publication Date: January 13, 2007
Citation: Calla, B., Zhang, Y., Simmonds, D., Clough, S.J. 2007. Genomic analysis of soybean resistance to Sclerotinia sclerotiorum. Plant and Animal Genome XV Conference. January 13-17, 2007. San Diego, CA. p. 284.

Technical Abstract: Sclerotinia sclerotiorum is a necrotrophic fungal pathogen that infects soybean causing white mold disease. Oxalic acid is considered to be its major virulence factor. Plants from the oxalate oxidase (OxO) transgenic line (80(30)1) which showed resistance to the pathogen and its susceptible parent line (AC Colibri) were inoculated using infected flower buds. Samples of the leaflets were taken at two stages of the disease within 24 hours of inoculation. In a different experiment, fifteen-days-old soybean plants of a partially resistant variety (PI 194639) and a susceptible variety (Williams 82) were inoculated with actively growing mycelia utilizing the cut-stem technique and 1 inch sections were sampled at 8 and 14 hours post inoculation for microarray gene expression analysis. The data were obtained as the log2 of the normalized intensities for each gene and statistically analyzed using linear models in SAS. The genes with highest p-values (cutoff 0.05) for the difference between both varieties in the OxO experiment were assigned into functional categories and clustered using fuzzy-k-means. The results show that genes related to defense, oxidative stress and secondary metabolism are mostly down-regulated in the OxO transgenic compared to its parent. These preliminary results suggest that the susceptible line is actively trying to defend, whereas the transgenic is apparently depleting the oxalic acid levels at the beginning of the interaction minimizing the need for activation of defense genes. A cross comparison between the two experiments supports that the resistance in the OxO plants differs from that expressed in the stems of PI 194639.