Cadmium Accumulation in Plants: Insights from Phylogenetic Variation into the Evolution and Functions of Membrane Transporters

Rapid industrialization during recent decades has resulted in the widespread contamination by cadmium (Cd) of agricultural soils, which has become a ubiquitous environmental problem and poses great risk to human health via the food chain. Cd accumulation greatly varies among different plant species and even within different genotypes of the same species across the plant kingdom. A better understanding of the physiological and molecular mechanisms underlying Cd uptake, translocation, sequestration, and (re)distribution in plants will shed light on developing strategies to minimize Cd in crops. Moreover, analysis of molecular evolution of the key transporters reveals that Cd transporters were highly conserved throughout the evolutionary lineage of the entire plant kingdom and underwent lineage-specific expansion as the result of gene duplication. However, different Cd transporters may experience different evolutionary lineages from algae to angiosperms, suggesting the divergence of their roles in plant adaptation to metalliferous soil. In summary, all the knowledge in the present review can be used to predict the transfer of Cd from soils to plants, to further understand the origins of Cd-accumulating phenotypes, and to discover the plant genetic resources for the breeding of low-Cd crops and the phytoremediation of Cd-contaminated soils.