Plant growth and development relies on the movement of mineral ions from the soil to the transport system of root cells (xylem tissue) and subsequent transfer to the shoot. Because this process usually occurs against a concentration gradient, passive diffusion is prevented and homeostasis ensured by the presence of a waterproof lignin-rich barrier known as the Casparian strip that surrounds xylem and phloem tissue in a ring. Several proteins were known to be necessary for Casparian strip formation, including the receptor kinase GSO1/SGN3.