A type 2C protein phosphatase activates high-affinity nitrate uptake by dephosphorylating NRT2.1

ABSTRACT Signal transduction protein PII is dephosphorylated in Synechocystis sp. strain PCC 6803 by protein phosphatase PphA. To determine the impact of PphA-mediated PII dephosphorylation on physiology, the phenotype of a PphA-deficient mutant was analyzed. Mutants lacking either PphA or PII were impaired in efficient utilization of nitrate as the nitrogen source. Under conditions of limiting photosystem I (PSI)-reduced ferredoxin, excess reduction of nitrate along with impaired reduction of nitrite occurred in PII signaling mutants, resulting in excretion of nitrite to the medium. This effect could be reversed by increasing the level of PSI-reduced ferredoxin. We present evidence that nonphosphorylated PII controls the utilization of nitrate in response to low light intensity by tuning down nitrate uptake to meet the actual reduction capacity. This control mechanism can be bypassed by exposing cells to excess levels of nitrate. Uncontrolled nitrate uptake leads to light-dependent nitrite excretion even in wild-type cells, confirming that nitrate uptake controls nitrate utilization in response to limiting photon flux densities.

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Regulation of High-Affinity Nitrate Uptake in Roots of Arabidopsis Depends Predominantly on Posttranscriptional Control of the NRT2.1/NAR2.1 Transport System

PLANT PHYSIOLOGY ◽

10.1104/pp.111.188532 ◽

2011 ◽

Vol 158 (2) ◽

pp. 1067-1078 ◽

Cited By ~ 49

Author(s):

Edith Laugier ◽

Eléonore Bouguyon ◽

Adeline Mauriès ◽

Pascal Tillard ◽

Alain Gojon ◽

...

Keyword(s):

Transport System ◽

Nitrate Uptake ◽

Posttranscriptional Control ◽

High Affinity

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PPM1H phosphatase counteracts LRRK2 signaling by selectively dephosphorylating Rab proteins

10.1101/711176 ◽

2019 ◽

Author(s):

Kerryn Berndsen ◽

Pawel Lis ◽

Wondwossen Yeshaw ◽

Paulina S. Wawro ◽

Raja S. Nirujogi ◽

...

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Protein Phosphatase ◽

Primary Cilia ◽

Rab Proteins ◽

Rab Gtpases ◽

Knock Out ◽

High Affinity ◽

Biochemical Studies ◽

Cilia Formation

AbstractMutations that activate LRRK2 protein kinase cause Parkinson’s disease. LRRK2 phosphorylates a subset of Rab GTPases within their Switch-II motif controlling interaction with effectors. An siRNA screen of all protein phosphatases revealed that a poorly studied protein phosphatase, PPM1H, counteracts LRRK2 signaling by specifically dephosphorylating Rab proteins. PPM1H knock out increased endogenous Rab phosphorylation and inhibited Rab dephosphorylation. Overexpression of PPM1H suppressed LRRK2-mediated Rab phosphorylation. PPM1H also efficiently and directly dephosphorylated Rab8A in biochemical studies. A “substrate-trapping” PPM1H mutant (Asp288Ala) binds with high affinity to endogenous, LRRK2-phosphorylated Rab proteins, thereby blocking dephosphorylation seen upon addition of LRRK2 inhibitors. PPM1H is localized to the Golgi and its knockdown suppresses primary cilia formation, similar to pathogenic LRRK2. Thus, PPM1H acts as a key modulator of LRRK2 signaling by controlling dephosphorylation of Rab proteins. PPM1H activity enhancers could offer a new therapeutic approach to prevent or treat Parkinson’s disease.

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

10.1101/583542 ◽

2019 ◽

Author(s):

Aurore Jacquot ◽

Valentin Chaput ◽

Adeline Mauries ◽

Zhi Li ◽

Pascal Tillard ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Transgenic Plants ◽

Translational Regulation ◽

Nitrate Uptake ◽

Phosphorylation Site ◽

Relative Level ◽

High Affinity ◽

Proteomic Approach ◽

C Terminus ◽

Main Component

AbstractIn 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.

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