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Identification of Sclerotinia sclerotiorum Effector Proteins mediating virulence on Arabidopsis thaliana ecotypes

Final Report Summary - SEPARATE (Identification of Sclerotinia sclerotiorum Effector Proteins mediating virulence on Arabidopsis thaliana ecotypes)

Sclerotinia sclerotiorum is a ubiquitous fungus causing white and stem rot diseases on more than 400 host plants, including oil, vegetable and tuber crops. In most cases, genetic sources of resistance to S. sclerotiorum are very limited. As with other necrotrophic fungi, damages caused by S. sclerotiorum are due to the secretion of a battery of hydrolytic enzymes, small secreted proteins and low molecular weight metabolites. However, the identity of S. sclerotiorum secreted proteins and metabolites critical for virulence, their biosynthesis pathways and plant targets mediating response to this fungus are still largely unknown.
To document the diversity of metabolic networks in Sclerotinia, we collected isolates of S. sclerotiorum and fungal pathogen species closely related to S. sclerotiorum. We analyzed isolates aggressiveness on seven Arabidopsis thaliana core accessions revealing a wide range of aggressiveness among Sclerotinia isolates, and pinpointing Arabidopsis candidate genes associated with resistance to specific isolates. Next, we set up a method to homogenize mycelium inoculums and determined culture conditions in which fungal metabolic activity can be extrapolated from fungal growth measurement with the Biolog technology. Using this approach, we found that S. sclerotiorum uses for in vitro growth numerous carbohydrate compounds, including carbohydrate polymers and some modified carbohydrates, but not amino acids nor fatty acids. We characterized the metabolic abilities of related Sclerotiniaceae species of fungal pathogens with distinct lifestyles for over 280 compounds. This analysis highlighted the versatility of S. sclerotiorum metabolism, the species with the broadest host range. These results open the way to a better understanding of the diversity of metabolism in fungi in relation with virulence. The ability to derive energy from a range of carbon sources is key to the ability of microbes to colonize their niches, including host plants, and should provide valuable insights towards the management of plant diseases. Additional information on this and related projects can be found at