Silicon influx transporter responsible for silicon transport from the external solution to the root cells (PubMed:16572174). Is coupled with the silicon efflux transporter LSI2 in both exodermal and endodermal root cells for an efficient silicon transport across the cells into the stele (PubMed:17625566). 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:16572174). Is coupled with LSI2 transporter in roots for efficient uptake of arsenite, which is further dispatched in shoots and grains (PubMed:18626020). Mediates uptake of methylated arsenic species in roots (PubMed:19542298). Mainly expressed in the roots (PubMed:16033806, PubMed:16572174, PubMed:17905867). In roots, it localizes in the main and lateral roots, but not in root hairs (PubMed:16572174). Within a root, it localizes on the plasma membrane of the distal side of both exodermis and endodermis, where casparian strips exist (at protein level) (PubMed:16572174, PubMed:17905867). Expressed low levels in leaves and anthers (PubMed:16033806). Regulated by silicon level; the expression being decreased 4-fold by continuous silicon supply for 3 days. Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Belongs to the MIP/aquaporin (TC 1.A.8) family. NIP (TC 1.A.8.12) subfamily.