Fig. 2.

Integrative model illustrating the roles of NRT1.1s in rice. Plasma membrane-localized OsNRT1.1B (NRT1.1B) functions as a nitrate sensor in response to external nitrate, while tonoplast-localized OsNRT1.1A (NRT1.1A) possibly acts as an intracellular nitrate sensor in the perception of the cell’s nitrogen status. The NRT1.1B–OsSPX4 (SPX4) module is a key node involved in integrating nitrate and phosphate signals in rice. In the presence of nitrate, NRT1.1B senses external nitrate and recruits an E3 ligase, NBIP1, to promote SPX4 ubiquitination and degradation via the 26S proteasome, thereby releasing OsPHR2 and OsNLP3 (NLP3) to concurrently activate downstream phosphate and nitrate responses, respectively. In addition, NRT1.1B can change the rhizosphere microenvironment by modulating root microbes related to nitrogen transformation.