OsCBL1 modulates rice nitrogen use efficiency via negative regulation of OsNRT2.2 by OsCCA1.

BACKGROUND: For cereal crop breeding, it is meaningful to improve utilization efficiency (NUE) under low nitrogen (LN) levels while maintaining crop yield. OsCBL1-knockdown (OsCBL1-KD) plants exhibited increased nitrogen accumulation and NUE in the field of low N level. RESULTS: OsCBL1-knockdown (OsCBL1-KD) in rice increased the expression of a nitrate transporter gene OsNRT2.2. In addition, the expression of OsNRT2.2, was suppressed by OsCCA1, a negative regulator, which could directly bind to the MYB-binding elements (EE) in the region of OsNRT2.2 promoter. The OsCCA1 expression was found to be down-regulated in OsCBL1-KD plants. At the low Nitrogen (N) level field, the OsCBL1-KD plants exhibited a substantial accumulation of content and higher NUE, and their actual biomass remained approximately as the same as that of the wild type. CONCLUSION: These results indicated that down-regulation of OsCBL1 expression could upregulate the expression of OsNRT2.2 by suppressing the expression of OsCCA1and then increasing the NUE of OsCBL1-KD plants under low nitrogen availability.

OsCBL1 affects rice seedling growth by modulating nitrate and phosphate responses.

To sustain high crop yield, a comprehensive understanding of the processes by which plants sense and acquire nutrients is of great importance. For the efficiency of crop fertilizer, it is essential to exploring the the signaling networks that coordinate the usage of nitrogen and phosphorus, the most demanding two mineral nutrients in plants. Here, we found that a protein OsCBL1 (Calcineurin B-like protein 1) is involved in the regulation of nitrogen and phosphorus signaling in rice. The nitrogen element, existing as ammonium or nitrate in the environment, affects nitrate signaling in vivo and root growth. Compared with the wild type, knockdown of OsCBL1 inhibit the growth of rice to the same extent, when nitrogen is deficient or nitrogen is present in the form of ammonium-nitrate mixture. The growth inhibition by OsCBL1-knockdown is more pronounced when nitrogen is present as ammonium. The phosphorus starvation-responsive genes is also regulated by the compound of nitrogen present in vitro and OsCBL1, while the phosphorus content is not affected. These results suggest that OsCBL1 may be involved in the response of rice to nitrogen and phosphorus nutrition in the environment, as well as the regulation of rice growth by environmental nutrition.