OsCBL1-mediated regulation of drought stress responses in rice

Calcineurin B-like proteins (CBLs) are important calcium sensors that play critical roles in plant growth, development and stress responses. However, the function of OsCBL1 in drought stress tolerance in rice remains unexplored. In this study, we investigated the role of OsCBL1 in response to drought using WT and OsCBL1-knockdown (OsCBL1-KD) rice lines through phenotypic, physiological and transcriptomic analyses. OsCBL1 was predominantly expressed in leaves and was strongly induced by drought stress. Phenotypic analysis revealed that OsCBL1-KD lines exhibited significantly reduced survival rates and increased water loss rates compared with WT plants following drought stress, indicating that the rice response to drought stress is dependent on OsCBL1. Physiological measurements showed that, under drought stress, OsCBL1-KD lines had significantly lower SOD activity, reduced H₂O₂ accumulation, decreased proline content and reduced chlorophyll content, but significantly higher MDA content compared with WT plants, suggesting compromised antioxidant capacity, impaired osmotic adjustment, and exacerbated oxidative damage. Transcriptomic analysis identified 457 OsCBL1-dependent drought-responsive genes, with up-regulated genes enriched in MAPK signaling and plant hormone signal transduction pathways and down-regulated genes enriched in protein processing in the endoplasmic reticulum and glutathione metabolism pathways. Additionally, six drought-associated transcription factors (OsbHLH148, OsZFP36, OsWOX13, OsbZIP71, OsbHLH130, and OsPIL13) were identified, constituting a predicted OsCBL1-mediated transcriptional regulatory network. Taken together, these results suggest that OsCBL1 acts as a key regulator of drought tolerance in rice by integrating MAPK cascades, hormone signaling, and redox homeostasis, providing new insights into CBL-mediated stress adaptation mechanisms.