Natural expression variation for the Arabidopsis MED20a Mediator complex subunit influences quantitative resistance to Sclerotinia sclerotiorum

Authors: Underwood, William; POUDEL, ROSHAN SHARMA - North Dakota State University

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2025
Publication Date: 11/17/2025
Citation: Underwood, W., Poudel, R. 2025. Natural expression variation for the Arabidopsis MED20a Mediator complex subunit influences quantitative resistance to Sclerotinia sclerotiorum. Frontiers in Plant Science. 16:1706963. https://doi.org/10.3389/fpls.2025.1706963.
DOI: https://doi.org/10.3389/fpls.2025.1706963

Interpretive Summary: The fungus Sclerotinia sclerotiorum is a plant pathogen that infects its hosts by killing plant cells, resulting in spreading lesions that lead to white mold disease. This fungus can infect many plant hosts, including important crop and vegetable species such as soybean, canola, sunflower, lettuce, carrot and dry bean. S. sclerotiorum can also cause disease on Arabidopsis thaliana, an important model system for studying fundamental aspects of plant biology, including resistance to disease. In this study, a large scale genetic mapping project was undertaken using natural ecotypes of A. thaliana and two isolates of S. sclerotiorum differing in their aggressiveness in causing disease. These genetic mapping efforts identified 30 genomic regions significantly associated with resistance to S. sclerotiorum. Surprisingly, no genomic regions were mapped for resistance to both isolates of the pathogen. Follow up studies identified a specific gene at one of the associated genomic positions that contributes to resistance to S. sclerotiorum. Additional study of these mapped regions should allow researchers to identify specific genes and processes governing defense against this pathogen and accelerate efforts to breed crop plants for improved resistance to white mold.

Technical Abstract: Introduction: The necrotrophic fungus Sclerotinia sclerotiorum is a destructive plant pathogen that can infect a broad range of host plants, including many agriculturally important crop species. Resistance to S. sclerotiorum is partial and quantitative, controlled by many genes. The identities of genes influencing resistance and the molecular mechanisms governing defense against this pathogen are poorly understood. To improve understanding of resistance, we performed genome-wide association studies of Arabidopsis thaliana response to inoculation with two isolates of the pathogen differing in aggressiveness and sought to validate our results by identifying the causal gene at a single mapped locus. Methods: A total of 325 A. thaliana ecotypes were evaluated for resistance at two timepoints after inoculation with S. sclerotiorum isolated 1980 or BN325. Genome-wide association studies were carried out using two different models to identify loci association with resistance. A. thaliana mutant lines were then evaluated for candidate genes at a single locus to identify the most likely candidate gene influencing resistance and sequencing of the candidate gene and promoter region were performed to identify putative causal variants. Results and discussion: Genome-wide association studies mapped 30 loci associated with resistance to S. sclerotiorum. Surprisingly, correlations for response to the two isolates among A. thaliana ecotypes were relatively weak and no overlapping loci were mapped for resistance to both isolates. A. thaliana med20a mutants impaired in a subunit of the transcriptional Mediator complex were more susceptible to S. sclerotiorum and a single variant upstream of the MED20a gene was associated with resistance. These results improve our mechanistic understanding of resistance to this important plant pathogen.