Abstract
A gene responsible for Si uptake has been cloned from rice, a typical Si-accumulating plant. Unexpectedly, this gene belongs to a Nod26-like major intrinsic protein (NIP) subfamily, which is predicted to have six transmembrane domains and two Asn-Pro-Ala (NPA) motif. Lsi1 is mainly expressed in the roots and the expression is decreased by one fourth by Si supply. Interestingly, Lsi1 is expressed in the main roots and lateral roots, but not in root hair. Further investigations show that the transport protein is localized only on the exterior side of plasma membrane of both exodermis and endodermis, where Casparian strips exist. When this gene is suppressed, the Si uptake is also reduced correspondingly. Furthermore, when the cRNA encoding Lsi1 was injected into Xenopus laevis oocytes, an increased transport activity for silicic acid was observed. All these evidence show that Lsi1 is a transporter for silicon in rice roots.
