OsCASP1 Is Required for Casparian Strip Formation at Endodermal Cells of Rice Roots for Selective Uptake of Mineral Elements.

In response to diverse environmental conditions, rice () roots have developed one Casparian strip (CS) at the exodermis and one CS at the endodermis. Here, we functionally characterized OsCASP1 (Casparian strip domain protein 1) in rice. was mainly expressed in the root elongation zone, and the protein encoded was first localized to all sides of the plasma membrane of endodermal cells without CS, followed by the middle of the anticlinal side of endodermal cells with CS. Knockout of resulted in a defect of CS formation at the endodermis and decreased growth under both soil and hydroponic conditions. Mineral analysis showed that the mutants accumulated more Ca, but less Mn, Zn, Fe, Cd, and As in the shoots compared with the wild type. The growth inhibition of the mutants was further aggravated by high Ca in growth medium. The polar localization of the Si transporter Low Si 1 at the distal side of the endodermis was not altered in the mutant, but the protein abundance was decreased, resulting in a substantial reduction in silicon uptake. These results indicated that is required for CS formation at the endodermis and that the CS in rice plays an important role in root selective uptake of mineral elements, especially Ca and Si.