Genetic architecture of a plant adaptive trait: QTL mapping of intraspecific variation for tolerance to metal pollution in Arabidopsis halleri.

Anthropogenic activities are among the main drivers of global change and result in drastic habitat modifications, which represent strong evolutionary challenges for biological species that can either migrate, adapt, or disappear. In this context, understanding the genetics of adaptive traits is a prerequisite to enable long-term maintenance of populations under strong environmental constraints. To examine these processes, a QTL approach was developed here using the pseudometallophyte Arabidopsis halleri, which displays among-population adaptive divergence for tolerance to metallic pollution in soils. An F2 progeny was obtained by crossing individuals from metallicolous and non-metallicolous populations from Italian Alps, where intense metallurgic activities have created strong landscape heterogeneity. Then, we combined genome de novo assembly and genome resequencing of parental genotypes to obtain single-nucleotide polymorphism markers and achieve high-throughput genotyping of the progeny. QTL analysis was performed using growth parameters and photosynthetic yield to assess zinc tolerance levels. One major QTL was identified for photosynthetic yield. It explained about 27% of the phenotypic variance. Functional annotation of the QTL and gene expression analyses highlighted putative candidate genes. Our study represents a successful approach combining evolutionary genetics and advanced molecular tools, helping to better understand how a species can face new selective pressures of anthropogenic origin.