NRT2.1 C‐terminus phosphorylation prevents root high affinity nitrate uptake activity in Arabidopsis thaliana

Abstract

In Arabidopsis thaliana, NRT2.1 codes for a main component of the root nitrate high-affinity transport system. Previous studies revealed that post-translational regulation of NRT2.1 plays an important role in the control of root nitrate uptake and that one mechanism could correspond to NRT2.1 C-terminus processing. To further investigate this hypothesis, we produced transgenic plants with truncated forms of NRT2.1. This revealed an essential sequence for NRT2.1 activity, located between the residues 494 and 513. Using a phospho-proteomic approach, we found that this sequence contains one phosphorylation site, at serine 501, which can inactivate NRT2.1 function when mimicking the constitutive phosphorylation of this residue in transgenic plants. This phenotype could neither be explained by changes in abundance of NRT2.1 and NAR2.1, a partner protein of NRT2.1, nor by a lack of interaction between these two proteins. Finally, the relative level of serine 501 phosphorylation was found to be increased by ammonium nitrate in wild-type plants, leading to the inactivation of NRT2.1 and to a decrease in high affinity nitrate transport into roots. Altogether, these observations reveal a new and essential mechanism for the regulation of NRT2.1 activity.

On the roots of nitrogen uptake

“…In the study of Jacquot et al . (2020), data obtained by native gel electrophoresis suggested that also NRT2.1 and NAR2.1 interact in high‐molecular‐weight oligomeric complexes, the largest of which was detected at c . 480 kDa.…”

“…Jacquot et al . (2020) add to this understanding by elucidating a molecular mechanism that inactivates NO 3 − uptake, presumably to protect the plant against over‐accumulation of this important nutrient.…”

“…In this issue of New Phytologist , Jacquot et al . (2020; pp. 1038–1054) report a new molecular mechanism, where phosphorylation of the NO 3 − transporter NRT2.1 on a C‐terminal serine residue regulates NO 3 − uptake in the model plant Arabidopsis thaliana .…”

“…In their study, Jacquot et al . (2020) applied these techniques and identified a critical role for S501 phosphorylation in the regulation of NRT2.1 root NO 3 − uptake activity. Characterization of transgenic Arabidopsis lines carrying phosphodeletion or phosphomimetic versions of NRT2.1 supported a model where phosphorylation of NRT2.1 at the C‐terminal S501 inactivates the enzyme, with a concomitant repression of root NO 3 − uptake.…”

“…The study by Jacquot et al . (2020) opens new research lines for uncovering the molecular mechanisms underlying N uptake in plants. Reflecting the importance of S501 phosphorylation in NRT2.1 regulation, this residue appears to be strongly conserved among different Arabidopsis accessions and other plant species in which NRT2.1 homologs can be identified.…”