2.A.17.3.24
NRT1.13; NPF4.4; PTR family 4.4 of 601 aas and 12 or 13 TMSs in a 6 or 7 + 6 TMS arrangement. In contrast to most NRT1 transporters, NRT1.13 does not have the conserved proline residue between TMSs 10 and 11, an essential residue for nitrate transport activity in CHL1/NRT1.1/NPF6.3 ( TC# 2.A.17.3.1). NRT1.13 showed no nitrate transport activity, but when Ser487 at the corresponding position was converted to proline, NRT1.13 S487P gained nitrate uptake activity, suggesting that wild-type NRT1.13 cannot transport nitrate but can bind it (Chen et al. 2021). Subcellular localization  indicated that NRT1.13 is a plasma membrane protein expressed at the parenchyma cells next to xylem in the petioles and the stem nodes. When plants were grown with a normal concentration of nitrate, the nrt1.13 mutant showed no severe growth phenotype, but when grown under low-nitrate conditions, nrt1.13 showed delayed flowering, increased node number, retarded branch outgrowth, and reduced lateral nitrate allocation to nodes. This suggested that NRT1.13 is required for low-nitrate acclimation and that internal nitrate is monitored near the xylem by NRT1.13 to regulate shoot architecture and flowering time.