Abstract
Metal transport processes are relatively poorly understood in algae in comparison to higher plants and other eukaryotes. A screen of genomes from 33 taxonomically diverse algal species was conducted to identify members of the Cation Diffusion Facilitator (CDF) family of metal ion transporter. All algal genomes contained at least one CDF gene, further confirming that this is a ubiquitous gene family. Phylogenetic analysis suggested a CDF gene organisation of five groups, which includes Zn-CDF, Fe/Zn-CDF and Mn-CDF groups, consistent with previous phylogenetic analyses, and two undefined groups. One of these undefined groups was algal specific although excluded chlorophyte and rhodophyte sequences. Sequences from this group had a putative ion binding site motif that was distinct from other CDF proteins. The phylogenetic grouping was supported by sequence cluster analysis. Yeast heterologous expression of CDF proteins from Chlamydomonas reinhardtii indicated Zn2+, Co2+ and/or Mn2+ transport function by the different isoforms, which validated the phylogenetic prediction, although one member of the Mn-CDF group was also able to provide Zn tolerance to yeast. There is wide diversity of CDF transporters within the algae lineage, and some of these genes may be attractive targets for future applications of metal content engineering in plants or microorganisms.