## 4 Evolution of Cadmium Transporters and Their Functions in Cadmium Accumulation
### Evolution of Cd Transporters
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Clade** & **Plant Species** & **NRAMPs** & **HMAs** & **ZIPs** & **CDFs** & **ABCCs** & **CAXs** & **OPTs** \\ \hline \multirow{9}{*}{Eudicots} & _Arabidopsis thaliana_ & 6 & 8 & 15 & 12 & 15 & 11 & 9 \\  & _Brassica rapa_ & 9 & 15 & 28 & 18 & 17 & 12 & 11 \\  & _Gossypium raimondii_ & 10 & 9 & 21 & 15 & 26 & 10 & 8 \\  & _Theobroma cacao_ & 6 & 7 & 12 & 13 & 15 & 6 & 10 \\  & _Eucalyptus ggnndis_ & 9 & 9 & 20 & 18 & 33 & 5 & 25 \\  & _Malus domestic_ & 10 & 17 & 16 & 26 & 24 & 12 & 18 \\  & _Medicago truncatula_ & 7 & 10 & 13 & 13 & 38 & 8 & 13 \\  & _Glycine max_ & 13 & 18 & 19 & 23 & 37 & 17 & 13 \\  & _Populus trichocarpa_ & 8 & 13 & 16 & 22 & 24 & 8 & 13 \\  & _Vitis vinifera_ & 6 & 5 & 13 & 11 & 23 & 5 & 11 \\  & _Solanum Lycopersicum_ & 4 & 8 & 11 & 12 & 14 & 7 & 8 \\  & _Chenopodium quinoa_ & 10 & 18 & 18 & 15 & 45 & 6 & 10 \\ \hline \multirow{9}{*}{Monocots} & _Spirodela polyrhiza_ & 3 & 8 & 9 & 11 & 12 & 7 & 6 \\  & _Zostera marina_ & 5 & 7 & 13 & 9 & 10 & 6 & 4 \\  & _Phoenix dactylifera_ & 10 & 21 & 14 & 19 & 32 & 16 & 11 \\  & _Tritcium aestivum_ & 18 & 26 & 25 & 19 & 53 & 15 & 22 \\  & _Hordeum vulgare_ & 7 & 11 & 12 & 8 & 16 & 9 & 9 \\  & _Brachymodium distachyon_ & 7 & 9 & 11 & 10 & 20 & 8 & 8 \\  & _Phylostachy heterocycla_ & 7 & 9 & 11 & 10 & 11 & 10 & 9 \\  & _Zea mays_ & 8 & 12 & 10 & 11 & 12 & 11 & 8 \\  & _Sorghum bicolor_ & 8 & 11 & 12 & 8 & 16 & 10 & 8 \\  & _Oryza sativa_ & 7 & 8 & 11 & 9 & 16 & 7 & 9 \\ \hline Basal angiosperms & _Ambrella trichopoda_ & 3 & 7 & 8 & 8 & 14 & 4 & 8 \\ \hline \multirow{3}{*}{Gymnosperms} & _Pinus taeda_ & 13 & 8 & 11 & 8 & 11 & 11 & 34 \\  & _Pinus lambertiana_ & 9 & 11 & 13 & 10 & 10 & 7 & 11 \\  & _P_icae abies_ & 5 & 5 & 10 & 2 & 6 & 4 & 9 \\ \hline \multirow{3}{*}{Ferns} & _Azolla filiculides_ & 9 & 18 & 11 & 16 & 22 & 11 & 10 \\  & _Salvinia cuculata_ & 2 & 9 & 3 & 7 & 16 & 2 & 3 \\ \hline \multirow{2}{*}{Lycophytes} & _Selgingin mellendorffii_ & 6 & 12 & 5 & 8 & 23 & 2 & 6 \\ \hline \multirow{3}{*}{Mosses} & _Physcomitrella patens_ & 6 & 18 & 7 & 12 & 15 & 6 & 2 \\  & _Sphagnum fallax_ & 6 & 8 & 5 & 9 & 16 & 4 & 11 \\ \hline \multirow{3}{*}{Liverwords} & _Marchantia polymorpha_ & 5 & 6 & 5 & 5 & 15 & 3 & 5 \\ \hline \multirow{3}{*}{Streptophytes} & _Mesotaenium_ & 3 & 7 & 1 & 3 & 8 & 0 & 0 \\  & _Spirogloa musicola_ & 9 & 19 & 3 & 17 & 11 & 3 & 0 \\  & _Chara brautii_ & 1 & 3 & 2 & 2 & 2 & 2 & 0 \\  & _Klebsornidium flaccidatum_ & 3 & 6 & 2 & 5 & 3 & 1 & 0 \\ \hline \multirow{3}{*}{Chlorophyta} & _ChChlamydomonas reinhardtii_ & 2 & 4 & 2 & 4 & 4 & 3 & 0 \\  & _Volox carteri_ & 2 & 4 & 0 & 1 & 4 & 3 & 0 \\  & _Osteococcus sp._ & 1 & 5 & 1 & 3 & 2 & 2 & 0 \\ \hline \multirow{3}{*}{Rhodophyta} & _Cyanidioschyzon merolae_ & 2 & 1 & 1 & 1 & 1 & 0 & 0 \\  & _Porphyna vezoensis_ & 1 & 3 & 0 & 2 & 2 & 1 & 0 \\ \hline \hline \end{tabular} Note: Numbers are based on both literature search and bioinformatic analysis. Query Cd transporter genes are listed in Table S1. Genome sequence data were downloaded from the oneKP database. Genesis software (Version 2.0) was used to estimate the similarity between protein sequences. Candidate protein sequences were selected by BLASTP searches that satisfied the E value \(<10^{-10}\) and query coverage \(>50\%\) criteria. NRAMPs: natural resistance-associated macrophage proteins; HMAs: heavy metal ATPasses; ZIPs: zinc/iron-regulated transporter-like proteins (ZRT1/IRT1-like protein); CDFs: cation diffusion facilitators; OPTs: oligopeptide transporter family; ABCCs: adenosine triphosphate-binding cassette subfamily C proteins; CAXs: cation/H\({}^{+}\) exchangers.  
\end{table} 
Table 1: Number of predicted and published cadmium (Cd) transporter families in 41 plant and algal species. In order to understand the origin of Cd transporters, a further phylogenetic analysis was performed on the orthologs of two famous Cd transporters, NRAMP5 and HMA2, across the entire plant kingdom using the One Thousand Plant Transcriptome (oneKP) database [98].