N-mediated heading date-1 (Nhd1) regulates nitrogen uptake efficiency and root growth in rice (Plant Physiol)

In rice, the transcription factor N-mediated heading date-1 (Nhd1) activates the expression of Heading date 3a (Hd3a), a floral regulator gene and regulate flowering. Li et al. report the role of Nhd1 in nitrogen (N) use efficiency and N-dependent root growth in rice. nhd1 mutants were impaired in root growth when grown in low nitrate, high nitrate, and in low ammonium conditions. Nhd1 induces the expression of dual affinity nitrate transporter NRT2.4 and the putative ammonium transceptor AMT1.3 by recognising the NBS (Nhd1 binding site) motifs in the respective promoter regions. Under low ammonium supply, the rate of ammonium influx and root growth of amt1.3 and nhd1 mutants were similar. The root growth reduction, rate of nitrate uptake and impairment in nitrate translocation was similar in nrt2.4 and nhd1 mutants.  Nhd1 is thus an upstream regulator of N-form dependent root growth responses controlled by NRT2.4 and AMT1.3. The over-expression of AMT1.3 and NRT2.4 could rescue impaired N uptake of nhd1 lines, without altering flowering time and HD3a expression. Interestingly, when grown until maturity under field conditions, the total N uptake was significantly improved in nhd1 lines, even when the soil N was low. The improved N uptake efficiency of nhd1 lines was probably due to the extended growth duration, and, by to the delayed flowering, a more favorable temperature during the reproductive stage.  (Summary by Lekshmy Sathee @lekshmysnair) Plant Physiol. 10.1093/plphys/kiac178