Coselected genes determine adaptive variation in herbivore resistance throughout the native range of Arabidopsis thaliana
- aDepartment of Ecology and Evolution, University of Chicago, Chicago, IL 60637;
- bLaboratoire Génétique et Evolution des Populations Végétales, UMR CNRS 8198, Université des Sciences et Technologies de Lille–Lille 1, F-59655 Villeneuve d'Ascq Cedex, France;
- cCenter for Computational Genetics and Genomics, Temple University, Philadelphia, PA 19122;
- dInstitut National de la Recherche Agronomique, Laboratoire des Interactions Plantes–Microorganismes, UMR441, F-31326 Castanet-Tolosan, France; and
- eCNRS, Laboratoire des Interactions Plantes–Microorganismes, UMR2594, F-31326 Castanet-Tolosan, France
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Edited by Trudy F. C. Mackay, North Carolina State University, Raleigh, NC, and approved February 20, 2015 (received for review November 8, 2014)

Significance
How organisms adapt to the biotic and abiotic environment is a major question in evolutionary biology that addresses how natural selection shapes biodiversity. Using mass spectrometry, we characterized natural variation in major defense molecules, aliphatic glucosinolates, in hundreds of ecotypes of the model plant Arabidopsis thaliana, spanning the native range of the species. Using extensive genomic resources and field experiments, we provide strong evidence that populations are adapted to local herbivore communities along a striking longitudinal cline. In addition, we show that only a few genes of strong effect govern this natural variation and that alleles at these genes, located on different chromosomes, appear to have coevolved through epistatic selection.
Abstract
The “mustard oil bomb” is a major defense mechanism in the Brassicaceae, which includes crops such as canola and the model plant Arabidopsis thaliana. These plants produce and store blends of amino acid-derived secondary metabolites called glucosinolates. Upon tissue rupture by natural enemies, the myrosinase enzyme hydrolyses glucosinolates, releasing defense molecules. Brassicaceae display extensive variation in the mixture of glucosinolates that they produce. To investigate the genetics underlying natural variation in glucosinolate profiles, we conducted a large genome-wide association study of 22 methionine-derived glucosinolates using A. thaliana accessions from across Europe. We found that 36% of among accession variation in overall glucosinolate profile was explained by genetic differentiation at only three known loci from the glucosinolate pathway. Glucosinolate-related SNPs were up to 490-fold enriched in the extreme tail of the genome-wide
Footnotes
↵1B.B. and C.G.M. contributed equally to this work.
- ↵2To whom correspondence should be addressed. Email: jbergels{at}uchicago.edu.
Author contributions: B.B., C.G.M., and J.B. designed research; B.B., C.G.M., R.V., and F.R. performed research; A.P. and T.C.M. contributed new reagents/analytic tools; B.B. and C.G.M. analyzed data; and B.B., C.G.M., and J.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1421416112/-/DCSupplemental.
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