Location: Sunflower and Plant Biology Research
Project Number: 3060-21220-031-21-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 1, 2017
End Date: Aug 31, 2021
By exploiting the wealth of genomics resources available for the model system Arabidopsis thaliana, we conducted a genome-wide association study (GWAS) to discover the identities and functions of genes contributing to quantitative Sclerotinia sclerotiorum resistance in Arabidopsis and to describe the resistance mechanism(s). An objective of this proposal is to confirm which of these genes contribute to Sclerotinia resistance and subsequently can be used as a comparative dataset to identify likely candidate genes for sunflower head rot and stalk rot resistance in genomic intervals identified by GWAS. This is particularly important in sunflower where resolution is limited by genome size and available marker density, and where validation of candidate genes is hampered by lack of functional tools. Presently, we have identified 32 Arabidopsis loci associated with Sclerotinia resistance and the mapping resolution afforded by the small genome size and high marker density for this model organism allowed for identification of clear candidate genes at these loci. The first aim of this project is therefore to functionally confirm the contribution of a selected subset of candidate genes to Sclerotinia resistance using publicly available T-DNA insertional mutant lines. Although plant lines with partial resistance to Sclerotinia often exhibit low yields and poor agronomic quality, which in some cases has been linked to specific QTL associated with Sclerotinia resistance, so far, no systematic evaluation has been undertaken to determine if very high levels of Sclerotinia resistance are correlated with low seed yield. Because our Arabidopsis GWAS study identified accessions with very high levels of resistance to Sclerotinia, a second aim of this project is to evaluate what impact accessions with high levels of Sclerotinia resistance have on seed production compared to non-resistant accessions. Comparing seed yield of resistant to non-resistant Arabidopsis accessions will allow us to rapidly and inexpensively evaluate potential negative correlations between high levels of Sclerotinia resistance and seed yield. The combination of confirmed genes and mechanisms contributing to Sclerotinia resistance along with information on effects of resistance on seed yield may facilitate rational strategies for combining favorable alleles at multiple loci to maximize resistance while minimizing negative effects on agronomic performance in affected crops. Specific objectives for the duration of the project are to: 1) Identify and validate homozygous Arabidopsis lines carrying T-DNA insertions in 15 selected candidate genes that were determined to be associated with resistance to Sclerotinia sclerotiorum during a genome-wide association study. 2) Evaluate T-DNA insertion mutants for altered susceptibility to S. sclerotiorum isolates 1980 and BN325. 3) Evaluate seed yield, seed size, and seed weight for ten Arabidopsis accessions determined to be highly resistant to S. sclerotiorum in comparison to ten randomly selected, non-resistant accessions.
This project will evaluate candidate Arabidopsis genes for resistance to Sclerotinia sclerotiorum and assess the impact of quantitative S. sclerotiorum resistance on Arabidopsis seed production. Arabidopsis T-DNA insertion mutant lines for 15 selected candidate genes potentially contributing to S. sclerotiorum resistance will be obtained from the Arabidopsis Biological Resource Center. NDSU and USDA-ARS will co-advise a postdoctoral associate, who will screen T-DNA insertion lines using a PCR assay to identify and confirm that lines are homozygous for insertions. Two independent lines per candidate gene will be evaluated for transcript abundance to confirm gene disruption and will subsequently be tested for altered response to two S. sclerotiorum using a disease assay developed by USDA-ARS. To evaluate impact of high levels of quantitative S. sclerotiorum resistance on seed production, ten highly resistant Arabidopsis accessions will be compared to ten randomly selected, non-resistant accessions by quantifying seed yield, seed size, and seed weight in replicated experiments. USDA-ARS will provide resistant and non-resistant Arabidopsis accessions and NDSU will collaborate with USDA-ARS to conduct evaluations.