Research article

A subgroup of plant aquaporins facilitate the bi-directional diffusion of As(OH)₃ and Sb(OH)₃ across membranes

Gerd P Bienert^1,5 , Michael Thorsen² , Manuela D Schüssler¹ , Henrik R Nilsson³ , Annemarie Wagner⁴ , Markus J Tamás² and Thomas P Jahn¹

¹Department of Agricultural Sciences, Faculty of Life Sciences, University of Copenhagen, Frederiksberg C, Denmark

²Department of Cell and Molecular Biology/Microbiology, University of Gothenburg, Göteborg, Sweden

³Department of Plant and Environmental Sciences, University of Gothenburg, Göteborg, Sweden

⁴Department of Chemistry, Atmospheric Science, University of Gothenburg, Göteborg, Sweden

⁵Current Address: UCL Université catholique de Louvain, Unité de biochemie physiologique, Croix du Sud 5/15, 1348 Louvain-la-Neuve, Belgium

author email corresponding author email

BMC Biology 2008, 6:26doi:10.1186/1741-7007-6-26

Published:	10 June 2008

Abstract

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.

Conclusion

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.