The calcium sensor OsCBL1 modulates nitrate signaling to regulate seedling growth in rice

Nitrate signaling integrates and coordinates gene expression and plant growth; however, the underlying molecular mechanisms involved remain poorly understood. Our previous study revealed that rice calcineurin B-like protein 1 (OsCBL1) modulates lateral root elongation by affecting auxin biosynthesis. Here, we report that OsCBL1 also modulates nitrate signaling to regulate rice seedlings growth. Compared with wild-type seedlings, seedlings of OsCBL1 -knockdown ( OsCBL1 -KD) plants showed a suppressed growth phenotype, which included reduced root and shoot fresh weights and shorter radicles, crown roots, and lateral roots, when grown in nitrogen-free conditions. Although the growth defects of OsCBL1 -KD plants could be partially rescued by the addition of nitrate to the growth conditions, the nitrate uptake capability of the OsCBL1 -KD plants did not differ from that of wild-type plants as assessed via nitrate content and 15 NO 3 − influx experiments. The nitrate-regulated expression of nitrate signal sentinel genes (Os NRT2 . 1 and Os NRT2 . 2 ) was affected in the OsCBL1 -KD plants under both long- and short-term nitrate treatments. Overall, our results showed a novel role for OsCBL1 in the regulation of nitrate signaling and nitrate-mediated rice growth.