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An efflux transporter of silicon in rice


Silicon is an important nutrient for the optimal growth and sustainable production of rice1,2,3,4. Rice accumulates up to 10% silicon in the shoot, and this high accumulation is required to protect the plant from multiple abiotic and biotic stresses1,2,3,4,5. A gene, Lsi1, that encodes a silicon influx transporter has been identified in rice6. Here we describe a previously uncharacterized gene, low silicon rice 2 (Lsi2), which has no similarity to Lsi1. This gene is constitutively expressed in the roots. The protein encoded by this gene is localized, like Lsi1, on the plasma membrane of cells in both the exodermis and the endodermis, but in contrast to Lsi1, which is localized on the distal side, Lsi2 is localized on the proximal side of the same cells. Expression of Lsi2 in Xenopus oocytes did not result in influx transport activity for silicon, but preloading of the oocytes with silicon resulted in a release of silicon, indicating that Lsi2 is a silicon efflux transporter. The identification of this silicon transporter revealed a unique mechanism of nutrient transport in plants: having an influx transporter on one side and an efflux transporter on the other side of the cell to permit the effective transcellular transport of the nutrients.

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Figure 1: Silicon uptake and phenotype of lsi2 mutant.
Figure 2: Expression and localization of Lsi2.
Figure 3: Efflux activity of Lsi2 in Xenopus oocytes.


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We thank H. Sato and Y. Nagato for providing M3 seeds, and M. Ishiguro for computer modelling. This research was supported by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan (to J.F.M.) and a grant of Green Technology Project from the Ministry of Agriculture, Forestry and Fisheries of Japan (to J.F.M.).

Author Contributions N.M. and N.Y. contributed equally to this work. J.F.M. and K.T. cloned the gene Lsi2 with the help of S.K. and M.Y.; N.Y. investigated the localization of Lsi2; and N.M. measured the transport activity of Lsi2. J.F.M. performed screening and physiological experiments and wrote the paper. All authors discussed the results and commented on the manuscript.

The nucleotide sequence data reported in this paper are deposited in the DDBJ/EMBL/GenBank nucleotide sequence databases under the accession number AB222273.

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Correspondence to Jian Feng Ma.

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Ma, J., Yamaji, N., Mitani, N. et al. An efflux transporter of silicon in rice. Nature 448, 209–212 (2007).

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