OsCBL10 negatively regulates salt tolerance at seedling stage in rice

Soil salinity increasingly endangers global rice production. Although CBL-CIPK complexes are known to decode salt-induced Ca²⁺surges to activate ion transporters and antioxidant pathways, the in vivo role of rice OsCBL10 remains unknown, leaving a critical gap in Ca²⁺-mediated salt-tolerance mechanisms. In this study, we demonstrate that OsCBL10 is a tonoplast-localized Ca²⁺sensor that is transcriptionally up-regulated by salinity and most highly expressed in anthers and salt-stressed shoots. CRISPR-Cas9 knockout lines (cbl10-1/2) exhibited higher survival, 25 % longer shoots and a 30 % lower shoot Na⁺/K⁺ ratio than wild-type (WT) plants under 100 mM NaCl, whereas over-expression lines (OE1/2) were hypersensitive. The improved tolerance of cbl10 mutants was linked to (i) enhanced Na⁺extrusion and K⁺retrieval, (ii) reduced H₂O₂ accumulation, and (iii) up-regulation of OsSOS1, OsNHX1 and OsMIOX. Thus, OsCBL10 functions as a tonoplast "brake" that dampens SOS signaling and ROS scavenging under salt stress. This study broadens the known roles of rice CBL proteins and highlights OsCBL10 as a key gene for engineering salt-resilient rice varieties.