Knockdown of the partner protein OsNAR2.1 for high-affinity nitrate transport represses lateral root formation in a...

The morphological plasticity of root systems is critical for plant survival, and understanding the mechanisms underlying root adaptation to nitrogen (N) fluctuation is critical for sustainable agriculture; however, the molecular mechanism of N-dependent root growth in rice remains unclear. This study aimed to identify the role of the complementary high-affinity NO3(-) transport protein OsNAR2.1 in NO3(-)-regulated rice root growth. Comparisons with wild-type (WT) plants showed that knockdown of OsNAR2.1 inhibited lateral root (LR) formation under low NO3(-) concentrations, but not under low NH4(+) concentrations. (15)N-labelling NO3(-) supplies (provided at concentrations of 0-10 mM) demonstrated that (i) defects in LR formation in mutants subjected to low external NO3(-) concentrations resulted from impaired NO3(-) uptake, and (ii) the mutants had significantly fewer LRs than the WT plants when root N contents were similar between genotypes. LR formation in osnar2.1 mutants was less sensitive to localised NO3(-) supply than LR formation in WT plants, suggesting that OsNAR2.1 may be involved in a NO3(-)-signalling pathway that controls LR formation. Knockdown of OsNAR2.1 inhibited LR formation by decreasing auxin transport from shoots to roots. Thus, OsNAR2.1 probably functions in both NO3(-) uptake and NO3(-)-signalling.