Si is the only element which alleviates multiple plant stresses including diseases, pests, and lodging. Rice is a typical Si-accumulating plant and requires high amount of Si for healthy growth.
We have been working on Si transporter in rice for many years. So far, we have identified three silicon transporters in rice. Lsi1 is an influx Si transporter (Nature, 440: 688-691, 2006), while Lsi2 is an efflux transporter (Nature, 448: 209-211, 2007). Both Lsi1 and Lsi2 are localized at both root exodermis and endodermis cells, but Lsi1 is at the distal side, while Lsi2 at the proximal side. Knockout of either Lsi1 or Lsi2 results in significant decrease of Si uptake, indicating that these two transporters are involved in Si uptake by the roots.
Recently, we identified a transporter, Lsi6, which is responsible for xylem unloading and inter-vascular transfer of Si. Lsi6 is localized at xylem parenchyma cells of leaf blade and leaf sheath Plant (Cell, 20: 1381-1389, 200). Lsi6 is also at xylem transfer cells in the nodes (Plant Cell, 2009).
In addition, we also have identified homologs of OsLsi1, OsLsi2 and OsLsi6 in barley and maize (Plant J, 2008; Plant Cell Physiol., 2009; Plant Cell, 2009). They differ in cell-specific localization and expression pattern.