Arabidopsis Casparian strip membrane domain proteins (CASPs) form a transmembrane scaffold to recruit lignin biosynthetic enzymes for Casparian strip (CS) formation. Rice is a semi-aquatic plant with a more complex root structure than Arabidopsis to adapt its growing conditions, where the different deposition of lignin and suberin is crucial for adaptive responses. Here, we observed the structure of rice primary and small lateral roots (SLRs), particularly the deposition patterns of lignin and suberin in wild type and Oscasp1 mutants. We found that the appearance time and structure of CS in the roots of rice are different from those of Arabidopsis and observed suberin deposition in the sclerenchyma in wild type roots. Rice CASP1 is highly similar to AtCASPs, but its expression is concentrated in SLR tips and can be induced by salt stress especially in the steles. The loss of OsCASP1 function alters the expression of the genes involved in suberin biosynthesis and the deposition of suberin in the endodermis and sclerenchyma and leads to delayed CS formation and uneven lignin deposition in SLRs. These different depositions may alter nutrient uptake, resulting in ion imbalance in plant, withered leaves, fewer tillers, and reduced tolerance to salt stress. Our findings suggest that OsCASP1 could play an important role in nutrient homeostasis and adaptation to the growth environment.

Arabidopsis Casparian strip membrane domain proteins (CASPs) form a transmembrane scaffold to recruit lignin biosynthetic enzymes for Casparian strip (CS) formation. Compared with Arabidopsis, rice root is more complex with a CS of the exodermis and sclerenchyma and a CS that does not block propidium iodide entry into the stele. Rice CASP1 is highly similar to AtCASPs, but it is not required for CS formation. Its mutation results in early leaf senescence and fewer tillers and does not change the CS structure and permeability. OsCASP1 is mainly located in the nuclear membrane. Its expression is concentrated in the root stele and at small lateral root tips and can be induced by salt stress. OsCASP1 mutation causes ectopic suberin deposition in small lateral roots and ion imbalances in the plant. Homeostatic disorder induces nutrient recycling and accelerate leaf senescence. To our knowledge, OsCASP1 is the first CASP to be described in the nuclear membrane; it modulates suberin deposition and does not involve CS formation, representing a novel regulatory mode of CASPs.Rice CASP1 regulates suberin deposition in small lateral roots and plays crucial role in metal homeostasis in plant