Silicon efflux transporter involved in silicon transport from the root cells to the apoplast. Is coupled with the silicon influx transporter NIP2-1/LSI1 in both exodermal and endodermal root cells for an efficient silicon transport across the cells into the stele. Silicon is beneficial to plant growth and helps plants to overcome abiotic and biotic stresses by preventing lodging (falling over) and increasing resistance to pests and diseases, as well as other stresses (PubMed:17625566). In the nodes, involved with LSI3 and NIP2-2/LSI6 in silicon intervascular transfer, which is required for the preferential distribution of silicon, such as hyperaccumulation of silicon in the husk (PubMed:26283388). Is coupled with NIP2-1/LSI1 transporter in roots for efficient uptake of arsenite, which is further dispatched in shoots and grains (PubMed:18626020). Constitutively expressed in roots. Localizes on the plasma membrane of the proximal side of both root exodermis and endodermis, where casparian strips exist (at protein level). Regulated by silicon level; the expression being decreased 4-fold by continuous silicon supply for 3 days. Belongs to the arsenite-antimonite (ArsB) efflux (TC 2.A.45) family. Truncated N-terminus.