Hegedus: A Genomics Approach to Sclerotinia Resistance in Brassica napus

Date: March 2010
Term: 3 years
Status: Completed
Researcher(s): Dwayne Hegedus, Roger Rimmer and Lone Buchwaldt, Agriculture and Agri-Food Canada, Saskatoon Research Station, SK
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a serious disease problem of canola worldwide. The long term objective for researchers at Agriculture and Agri-Food Canada is to provide the canola industry with specific resistance genes and molecular markers as a selection tool used by plant breeders for selection of stem rot resistant canola cultivars. The researchers are using a genomics approach to characterize sclerotinia resistance in resistant Brassica napus lines identified in a previous project. In a three-year study initiated in 2007, researchers identified candidate resistance genes using genomics methods and examined the contribution of selected genes to resistance. As a result of the project, genes expressed in B. napus cultivars resistant to S. sclerotiorum have been identified and genetic markers that will allow their introduction into elite canola varieties are being developed.

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a serious disease problem of canola worldwide. Canola breeders and producers have a long-term goal of obtaining sclerotinia resistant canola crops. The objective of the research was to identify specific resistance genes and to design molecular markers to support plant breeders in the development of stem rot resistant canola cultivars. The molecular markers will be used selecting resistant lines from crosses between resistant and agronomically optimal cultivars in breeding programs.

The objectives of the three-year project initiated in 2007 at the Agriculture and Agri-Food Canada Saskatoon Research Centre were to identify candidate resistance genes using genomics methods, such as expressed sequence tags (ESTs) and gene arrays, to examine the contribution of selected genes to resistance, and to develop a better understanding of the factors employed by the fungus to cause disease and to determine how the plant inactivates these factors.

In the first component, researchers at AAFC used a genomics approach to identify putative defense genes that were responsible for sclerotinia resistance in certain B. napus lines. The winter-type B. napus Zhongyou 821 developed in China was one of the first cultivars with resistance to stem rot, and the research was mainly carried out with this line. Using powerful techniques, such as DNA sequencing and DNA micro-arrays, researchers identified the genes expressed in Zhongyou 821 in response to S. sclerotiorum infection. Several putative resistance genes were introduced into a susceptible B. napus line to determine their individual contribution to resistance.

In a parallel project, several mapping populations of doubled haploid (DH) lines were developed from crosses between Zhongyou 821 x susceptible lines. Several quantitative trait loci (QTL) contributing to resistance were identified in these populations. Some of the defense related genes identified by the genomics approach were mapped to these resistance loci. Vice versa, some of the QTL were shown to contain defense related genes identified in the DNA microarray study.

In addition, the researchers examined how S. sclerotiorum causes disease and the mechanisms used by the plant to prevent this. Five polygalacturonases (enzymes that break down plant cell walls) and two necrosis-inducing proteins were found to be the principal factors responsible for the development of necrotic lesions. Using a genomics approach, genes in B. napus encoding polygalacturonase inhibiting proteins were identified. This study provided new insight into aspects of the defense response to necrotrophic pathogens using an experimental design that resembles the interaction between S. sclerotiorum and B. napus.

Scientific Publications

Bashi, ZD, Rimmer, SR, Buchwaldt, L, Khachatourians GG and Hegedus D.D. (2012) Factors governing the regulation of Sclerotinia sclerotiorum cutinase A and polygalacturonase 1 during different stages of the infection. Can. J. Microbiol. (in press).

Bashi ZD, Hegedus, D.D., Buchwaldt, L., Rimmer, S.R. and Borhan, M.H. (2010) Expression and regulation of Sclerotinia sclerotiorum necrosis and ethylene inducing peptides (NEPs). Mol. Plant Pathol. 11: 43-53.

Bashi ZD, Khachatourians GG and Hegedus DD (2009) Isolation of fungal homokaryotic lines from heterokaryotic transformants by sonic disruption of mycelia. Biotechniques 48:351-354.

Zhao J., Buchwaldt, L., Rimmer R., Sharpe A., Bekkaoui D, Hegedus DD. (2009) Patterns of differential gene expression in Brassica napus cultivars infected with Sclerotinia sclerotirum. Mol. Plant Pathol. 10: 635-649.

Zhao, J., Buchwaldt, L., Rimmer, S.R., Brkic, M., Bekkaoui, D. and Hegedus, D.D. (2009) Differential expression of duplicated peroxidase genes in the allotetraploid Brassica napus. Plant Physiol. Biochem. 47: 653-656.

Hegedus DD, Li, R., Buchwaldt L., Parkin I., Whitwill S., Coutu C., Bekkaoui D, Rimmer SR. (2008). Brassica napus possesses an expanded set of polygalacturonase inhibitor protein genes that are differentially-regulated in response to Sclerotinia sclerotiorum infection, wounding and defence hormone treatment. Planta 228:241-253.

Li, R., Rimmer, R., Buchwaldt, L., Sharpe, A.G., Séguin-Swartz, G., and Hegedus, D.D.

(2004a) Interaction of Sclerotinia sclerotiorum with Brassica napus: Cloning and characterization of endo- and exo-polygalacturonases expressed during saprophytic and parasitic modes. Fungal Genet. Biol. 41: 754-765.

Li, R., Rimmer, R., Buchwaldt, L., Sharpe, A.G., Séguin-Swartz, G., and Hegedus, D.D.

(2004b) Interaction of Sclerotinia sclerotiorum with a resistant Brassica napus cultivar:

Expressed sequence tag analysis identifies genes associated with fungal pathogenesis. Fungal Genet. Biol. 41: 735-753.

Li, R., Rimmer, R., Yu, M., Sharpe, A.G., Séguin-Swartz, G., Lydiate, D. and Hegedus, D.D. (2003) Two polygalacturonase inhibitory protein genes are differentially expressed in response to biotic and abiotic stresses in Brassica napus. Planta 217: 299-308.

Full Report PDF: A Genomics Approach to Sclerotinia Resistance in Brassica napus