A subgroup of plant aquaporins facilitate the bi-directional diffusion of As(OH)3 and Sb(OH)3 across membranes.
BACKGROUND
Arsenic is a toxic and highly abundant metalloid that endangers human health through drinking water and the food chain. The most common forms of arsenic in the environment are arsenate (As(V)) and arsenite (As(III)). As(V) is a non-functional phosphate analog that enters the food chain via plant phosphate transporters. Inside cells, As(V) becomes reduced to As(III) for subsequent extrusion or compartmentation. Although much is known about As(III) transport and handling in microbes and mammals, the transport systems for As(III) have not yet been characterized in plants.


RESULTS
Here we show that the Nodulin26-like Intrinsic Proteins (NIPs) AtNIP5;1 and AtNIP6;1 from Arabidopsis thaliana, OsNIP2;1 and OsNIP3;2 from Oryza sativa, and LjNIP5;1 and LjNIP6;1 from Lotus japonicus are bi-directional As(III) channels. Expression of these NIPs sensitized yeast cells to As(III) and antimonite (Sb(III)), and direct transport assays confirmed their ability to facilitate As(III) transport across cell membranes. On medium containing As(V), expression of the same NIPs improved yeast growth, probably due to increased As(III) efflux. Our data furthermore provide evidence that NIPs can discriminate between highly similar substrates and that they may have differential preferences in the direction of transport. A subgroup of As(III) permeable channels that group together in a phylogenetic tree required N-terminal truncation for functional expression in yeast.


CONCLUSIONS
This is the first molecular identification of plant As(III) transport systems and we propose that metalloid transport through NIPs is a conserved and ancient feature. Our observations are potentially of great importance for improved remediation and tolerance of plants, and may provide a key to the development of low arsenic crops for food production.
Bienert
Gerd P
GP
Department of Agricultural Sciences, Faculty of Life Sciences, University of Copenhagen, Frederiksberg C, Denmark. gerd.bienert@uclouvain.be
Thorsen
Michael
M
Schüssler
Manuela D
MD
Nilsson
Henrik R
HR
Wagner
Annemarie
A
Tamás
Markus J
MJ
Jahn
Thomas P
TP
D000818:Animals; D000965:Antimony / Q000378:metabolism*; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics; D018053:Arsenites / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004058:Diffusion; D005786:Gene Expression Regulation; D017136:Ion Transport; D000070116:Lotus / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D046188:Protein Modification, Translational; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000235:genetics
D020346:Aquaporins; D018053:Arsenites; D008565:Membrane Proteins; D010940:Plant Proteins; C045625:nodulin; C061374:antimonite; D000965:Antimony; C015001:arsenite