Biology subjects

Lejay, L.

Publications and source records attributed to Lejay, L..

5 recordsLinked to original sources

bioRxiv2022

Signaling pathways involved in the repression of root nitrate uptake by nitrate in Arabidopsis thaliana

In Arabidopsis thaliana, root high-affinity nitrate (NO3-) uptake depends mainly on NRT2.1, 2.4 and 2.5, which are repressed by high NO3- supply at the transcript level. For NRT2.1, this regulation is due to the action of (i) feedback downregulation by N metabolites and (ii) repression by NO3- itself mediated by the transceptor NRT1.1(NPF6.3). However, for NRT2.4 and NRT2.5 the signaling pathway(s) remain unknown along with the molecular elements involved. Here we show that unlike NRT2.1, NRT2.4 and NRT2.5 are not induced in a NO3- reductase mutant but are strongly upregulated following replacement of NO3- by ammonium (NH4+) as the N source. Moreover, increasing NO3- concentration in a mixed nutrient solution with constant NH4+ concentration results in a gradual repression of NRT2.4 and NRT2.5, which is suppressed in a nrt1.1 mutant. This indicates that NRT2.4 and NRT2.5 are subjected to repression by NRT1.1-mediated NO3- sensing, and not to feedback repression by reduced N metabolites. We further show that key regulators of NRT2s transporters, such as HHO1, HRS1, PP2C, LBD39, BT1 and BT2, are also regulated by NRT1.1-mediated NO3- sensing, and that several are involved in NO3- repression of NRT2.1, 2.4 and 2.5. Finally, we provide evidence that it is the phosphorylated form of NRT1.1 at the T101 residue, which is most active in triggering the NRT1.1-mediated NO3- regulation of all these genes. Altogether, these data led to propose a regulatory model for high-affinity NO3- uptake in Arabidopsis, highlighting several NO3- transduction cascades downstream the phosphorylated form of the NRT1.1 transceptor. One sentence summaryCharacterisation and identification of molecular elements involved in the signaling pathways repressing NRT2s transporters and root nitrate uptake in response to nitrate.

plant biology↗

bioRxiv2020

A phospho-switch in the N-terminus of NRT2.1 affects nitrate uptake by controlling the interaction of NRT2.1 with NAR2.1

NRT2.1 can be phosphorylated at five different sites within N- and C-terminus. Here, we provide a systematic functional characterization of phosphorylation at S21 and S28 within the N-terminus of NRT2.1. We used existing phosphoproteomic data sets of nitrate starvation and nitrate resupply to construct a site-specific correlation network identifying kinase candidates to phosphorylate NRT2.1. By this approach, we identified NO_SCPCAPITRATEC_SCPCAP UO_SCPCAPPTAKEC_SCPCAP RO_SCPCAPEGULATORYC_SCPCAP KO_SCPCAPINASEC_SCPCAP 1 (AT5G49770) which itself was regulated by phosphorylation at S839 and S870 within its kinase domain. In the active state, when S839 was dephosphorylated and S870 was phosphorylated, NURK1 was found to interact with NRT2.1 at dephosphorylated S28. Upon that interaction, NURK1 can phosphorylate NRT2.1 at S21. Phosphorylation of NRT2.1 at S21 resulted in low interaction of NRT2.1 with its activator protein NAR2.1. By contrast, phosphorylation of NRT2.1 at S28 by a yet unknown kinase enhanced the interaction with NAR2.1, but inhibited the interaction with NURK1. We propose that serines S21 and S28 are involved in a phospho-switch mechanism and by which the interaction of NRT2.1 with its activator NAR2.1, and thus NRT2.1 activity, is modulated. NURK1 here was identified as the kinase affecting this phospho-switch through phosphorylation of NRT2.1 at S21 leading to inactivation of NRT2.1.

plant biology↗

bioRxiv2019

Genome-wide Analysis In Response to N and C Identifies New Regulators for root AtNRT2 Transporters

In Arabidopsis thaliana, the High-Affinity Transport System (HATS) for root NO3- uptake depends mainly on four NRT2 transporters, namely NRT2.1, NRT2.2, NRT2.4 and NRT2.5. The HATS is the target of many regulations to coordinate nitrogen (N) acquisition with the N status of the plant and with carbon (C) assimilation through photosynthesis. At the molecular level, C and N signaling pathways have been shown to control gene expression of the NRT2 transporters. Although several regulators of these transporters have been identified in response to either N or C signals, the response of NRT2 genes expression to the interaction of these signals has never been specifically investigated and the underlying molecular mechanisms remain largely unknown. To address this question we used an original systems biology approach to model a regulatory gene network targeting NRT2.1, NRT2.2, NRT2.4 and NRT2.5 in response to N/C signals. Our systems analysis of the data highlighted the potential role of three putative transcription factors, TGA3, MYC1 and bHLH093. Functional analysis of mutants combined with yeast one hybrid experiments confirmed that all 3 transcription factors are regulators of NRT2.4 or NRT2.5 in response to N or C signals.\n\nOne sentence summaryIdentification of three transcription factors involved in the regulation of NRT2s transporters using a systems biology approach and NRT2.1 as target gene in response to combinations of N/C treatments

plant biology↗

bioRxiv2019

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

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. It revealed an essential sequence for NRT2.1 activity, located between the residues 494-513. 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 modulated by nitrate in wildtype plants. Altogether, these observations allowed us to propose a model for a new and essential mechanism for the regulation of NRT2.1 activity.

plant biology↗

bioRxiv2018

HNI9 and HY5 maintain ROS homeostasis under high nitrogen provision in Arabidopsis

One sentence summaryExcessive N nutrition leads to ROS accumulation, and requires the function of major transcriptional regulators to maintain plants under physiological conditions.\n\nAuthor contributionsAn.M. and A.G. conceived research plans and supervised the experiments; F.B, Am.M., J.B., L.L., L.B. and An.M performed most of the experiments; F.B, Am.M., J.B., G.K., L.L., L.B. and An.M analyzed the data; An.M. wrote the article with contributions of all the authors.\n\nCompeting interestsThe authors declare no competing financial interests.\n\nSummaryReactive Oxygen Species (ROS) can accumulate in cells at excessive levels, leading to unbalanced redox status and to a potential oxidative stress, which can have damaging effects to the molecular components of plant cells. Several environmental conditions have been described as causing an elevation of ROS production in plants. Consequently, this requires the expression of detoxification responses in order to maintain ROS homeostasis at physiological levels. In case of mis-regulation of the detoxification systems, oxidative stress can lead ultimately to growth retardation and developmental defects. Here, we demonstrate that Arabidopsis plants growing under high nitrogen environment have to express a set of genes involved in detoxification of ROS in order to maintain ROS at physiological levels. We show that the chromatin factor HNI9 is an important actor of this response, required for the expression of these detoxification genes. Mutation in HNI9 leads to elevated ROS levels, and to ROS-dependent phenotypic defects under high but not low N provision. In addition, we identify HY5 as one of the major transcription factors also required for the expression of this detoxification program under high N condition. Our results demonstrate the requirement of a balance between N nutrition and ROS production, and identified the first major regulators required to control ROS homeostasis under excessive N nutrition.

plant biology↗