Trade-off between genetic variation and ecological adaptation of metallicolous and non-metallicolous Noccaea and Thlaspi species

Forty-seven accessions of Noccaea and Thlaspi grown in the presence of Ni were phenotyped for leaf mineral concentrations and morphology. Sequences of 9 target genes involved in metal homeostasis were compared in a Ni-adapted population of Noccaea caerulescens grown on the serpentine Monte Prinzera (MP), and in accessions from metalliferous and non-metalliferous soils. The MP population, which resembled most the Zn/Cd accumulators from Austria, showed little genetic variation. Higher levels of sequence variation found in target genes compared to non-target genes, suggest that selective pressure by exposure to high concentrations of metals may have led to adaptation to metalliferous environments, in trade-off with genetic variation. The ZNT2 zinc deficiency responsive zinc transporter gene showed significant variation in a selection test. The hydrophobicity profile of ZNT2 variants indicates, in this case, sequence variation is likely to affect the function of the encoded protein.