The GAPLESS-OsCASP complex mediates Casparian strip formation for proper localization and abundance of endodermal proteins in rice

Casparian strip (CS) seals the extracellular space between neighboring endodermal cells and helps plants maintain nutrient homeostasis. However, little is known about CS formation and function in rice. Here, we demonstrate that GAPLESS1/2/3, along with OsCASP1/2/3/5, redundantly regulate endodermal CS formation by forming an interdependent complex in rice. Triple knockout of GAPLESSs or quadruple knockout of OsCASPs resulted in delayed CS initiation, disrupted CS-CSD adhesion, and disordered CS at the endodermis. In these mutants, GAPLESS1, OsCASP1, and SCHENGEN3a (OsSGN3a) uniformly localized to the plasma membrane or cytoplasm in root tips, with lower abundance in endodermal cells. Furthermore, CS defects in these mutants triggered strong suberization on endodermal cells via OsSGN3a/b-mediated signaling, thereby restricting and reducing the accumulation of the Si transporter Lsi1 exclusively to nonsuberized cells. Like Oscasp1 , the triple gapless mutant exhibited large ionomic changes in shoots. Therefore, the GAPLESS-OsCASP complex functions in CS formation, with its roles in regulating ion homeostasis and protein localization and abundance.