Adaptation to toxic serpentine soils

Adaptation represents key evolutionary mechanism, which allows species and populations to succeed in a variable environment. Hostile serpentine soils are among the strongest triggers for adaptation in plants. 

This chemically extreme substrate provides multiple challenges to plant life, including extremely low Ca:Mg ratio and elevated levels of toxic metals. Therefore, serpentine barrens provide a powerful model for studying multi-challenge adaptations. Moreover, the island-like distribution of serpentines can trigger parallel evolution at the level of both genome and phenotype.

We assessed evolutionary sources of adaptive variation in lineages with doubled genomes, using autotetraploid Arabidopsis arenosa, which repeatedly adapted to naturally toxic serpentine soils. First, we combined demographic analysis and transplant experiments to demonstrate rapid parallel adaptation to five serpentine barrens. We identified shared  candidate genes for selection, functionally relevant to serpentines, e.g. genes, which are involved in dehydration tolerance and ion homeostasis. 

Then, we modelled parallel selection and infer dominant role of sampling from a shared pool of alleles across the variable tetraploid populations. However, we also discovered an exceptional locus with parallel de novo mutations! It encodes a central transporter TPC1 protein, shown to act as a global hub mediating stress signalling, with two distinct serpentine-specific mutations in otherwise conserved site at calcium selectivity gate.

Our finding demonstrates that large pool of pre-existing variation is the major source of adaptive alleles in autotetraploids. However, rapid selection on de novo mutations is still feasible, altogether indicating broad evolutionary flexibility of lineages with doubled genomes. You can discover more here.

We are digging deeper into serpentine adaptation and its convergent genetic basis across European Brassicaceae in the new ConAdapt project funded by the GACR Junior Star scheme.