OsCASP1 negatively regulates salt sensitivity and leaf senescence by modulating suberin deposition in rice roots

Casparian strip membrane domain proteins (CASPs) are required for Casparian strip (CS) formation. In rice, the loss of OsCASP1 leads to premature leaf senescence, increased salt sensitivity and ectopic suberin deposition. In order to elucidate the role of OsCASP1 in these biological pathways, the expression of related genes and the physiological phenotypes of the Oscasp1 mutant were analyzed. The present study demonstrates that OsCASP1 localizes to nuclear membranes in root tips, residing at both the nuclear and plasma membranes in root elongation zones. It also was detected in the endoplasmic reticulum of protoplasts. OsCASP2 is specifically localized to the Casparian strip membrane domain of the endodermis. OsCASP1 may assist OsCASP2 in CS formation. The Oscasp1 mutation reduces suberin deposition in the sclerenchyma and increases it in certain endodermal cells. Salt stress alters suberin deposition patterns, increasing deposition in the sclerenchyma and endodermis. Before and after salt stress, mutant roots have more passage or non-suberized cells in the endodermis compared to wild type plants. This results in an ion imbalance in the roots, stems and leaves, activating genes that positively regulate salt tolerance. However, the suberin lamellae appear more critical roles than the upregulation of these genes in the salt stress response. The combined effects of intense light stress and ion imbalance accelerate premature plant senescence. The Oscasp1 mutation reduces photosynthesis and redox homeostasis, promoting nutrient recycling and leaf senescence. OsCASP1 regulates suberin deposition and nutrient homeostasis, thereby influencing sensitivity to nutrient stress.