Cadmium (Cd) contamination in the environment has becoming a hot issue worldwide, as it has posed a great risk to human health through food chain. Cd accumulation in the edible parts of crops are involved in four processes: uptake, translocation, sequestration and (re)distribution, which are all controlled by membrane transporters. In this review, the advance in studies on physiological and molecular mechanisms of Cd accumulation in plants was summarized, and then the functional evolution was discussed based on oneKP database. Cd accumulation in plants is a derived and polyphyletic trait that has evolved convergently by several times. During their evolution, the membrane transporter families, such as NRAMPs, HMAs, ABCCs, ZIPs, CDFs, CAXs and OPTs, have undergone the lineage specific expansion due to gene duplication. The orthologues of OsHMA2 in higher plants are stepwisely evolved from monophyletic evolutionary lineage with one common ancestor; whereas the orthologues of OsNRAMP5 from a polyphyletic evolutionary lineage with several ancestors. In addition, phylogenetic clusters of the orthologues of OsNRAMP5 have occurred rampant intermixing, suggesting horizontal gene transfer. It may be concluded that evolution of Cd accumulation in plants could provide an adaptive advantage for colonization of plants to the new habitats like metalliferous soil.
