1. Research Institute for Bioresources, Okayama University, Chuo 2-20-1, Kurashiki 710-0046, Japan
2. Institute of Society for Techno-innovation of Agriculture, Forestry and Fisheries, Kamiyokoba, Tsukuba, Ibaraki, 305-0854, Japan
3. Biotechnology Research Center, The University of Tokyo, Bunkyo Ku, Tokyo, 113-8657, Japan
4. Solution Oriented Research for Science and Technology, Japan Science and Technology Agency, 3-4-15 Nihonbashi, Tokyo 103-0027, Japan
5. QTL Genomics Research Center, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan
6. These authors contributed equally to this work.

Correspondence to: Jian Feng Ma¹ Correspondence and requests for materials should be addressed to J.F.M. (Email: maj@rib.okayama-u.ac.jp).

Abstract

Silicon is an important nutrient for the optimal growth and sustainable production of rice^{1, 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 stresses^{1, 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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