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Abstract

Local adaptation and its underlying genetics are largely driven by natural enemies in Arabidopsis thaliana.

Understanding the genetics underlying adaptive variation has been a long-standing goal of evolutionary genetics. After presenting the genomic resources and the tools that make ofArabidopsis thalianaan ideal model to answer these fundamental questions, I will present results from two distinct projects.

The first is a genome-wide association study glucosinolate profile variation. Glucosinolates are molecules involved in herbivore defense in Brassicales. We studied the blend of molecules produced by 758 worldwide accessions (inbred lines) and detected both known and novel candidate genes for natural variation of the glucosinolate profile. Combining the results from the association study with a genome-wide FST scan, we found evidence for selection on multiple loci from this pathway across the genome. Our examination of glucosinolate profiles revealed a striking longitudinal gradient in β-hydroxylated alkenyl glucosinolates and we found significant contributions of glucosinolate loci to general herbivore resistance and lifetime fitness in common garden experiments conducted in France. Two glucosinolate loci,GS-OHandGS-ELONG,located on different chromosomes were strongly correlated and displayed effects on fitness and herbivore resistance in the field, suggesting that natural selection has locked the genome into locally adapted configurations.

The second project investigates the extent and the genetic basis of local adaptation in Arabidopsis populations from Sweden. Large common garden experiments including 200 re-sequenced Swedish accessions were used to measure important fitness components in two climatically contrasted regions of Sweden. We found evidence for local adaptation and investigated the underlying genetics using genome-wide association mapping. Our results suggest that pathogen resistance strongly contributes to fitness variation, in particular in the South of Sweden. A complementary set of natural selection experiments in both regions is being assayed three times a year, allowing us to track allele frequency changes and potentially locate regions of the genome responding to natural selection. Preliminary results seem to show consistency between the results of common garden experiments and selection experiments.
Overall our results suggest a strong impact of plant enemies on fitness in natural populations and their important role in shaping the genetics underlying adaptive variation inA. thaliana.

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