scholarly journals Abscisic-acid-dependent regulation of Arabidopsis thaliana ammonium transport relies on ABI1 control of CIPK23 and AMT1

2021 ◽  
Author(s):  
Pascal Ganz ◽  
Romano Porras-Murillo ◽  
Toyosi Ijato ◽  
Jochen Menz ◽  
Tatsiana Straub ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Abscisic Acid ◽  
Abiotic Stress ◽  
Protein Kinase ◽  
Growth Conditions ◽  
Plant Roots ◽  
Ammonium Uptake ◽  
Ammonium Transport ◽  
Ammonium Toxicity ◽  
Ammonium Transporters

SummaryAmmonium uptake at plant roots is regulated at the transcriptional, post-transcriptional and post-translational levels. Phosphorylation by the protein kinase CIPK23 transiently inactivates the ammonium transporters (AMT1s) but the phosphatases activating AMT1s remain unknown. Here, we have identified the PP2C phosphatase ABI1 as an activator of AMTs in Arabidopsis thaliana. We show that high external ammonium concentrations elevate the stress phytohormone abscisic acid (ABA) by de-glycosylation. Active ABA is sensed by ABI1-PYL complexes followed by the inactivation of ABI1 activating CIPK23. Under favourable growth conditions, ABI1 reduces AMT1 phosphorylation, both by binding and inactivating CIPK23, and by the direct dephosphorylation of AMT1s. Thus, ABI1 is a positive regulator of ammonium uptake, coupling nutrient acquisition to abiotic stress signalling. Elevated ABA reduces ammonium uptake during stress situations, such as ammonium toxicity, whereas ABI1 reactivates AMT1s under favourable growth conditions.

scholarly journals CALCIUM-DEPENDENT PROTEIN KINASE 32-mediated phosphorylation is essential for the ammonium transport activity of AMT1;1 in Arabidopsis roots

2020 ◽  
Vol 71 (16) ◽  
pp. 5087-5097
Author(s):  
De-Bin Qin ◽  
Meng-Yuan Liu ◽  
Lixing Yuan ◽  
Yun Zhu ◽  
Xi-Dong Li ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Ammonium Transporter ◽  
Ammonium Uptake ◽  
Ammonium Transport ◽  
Toxicity Screening ◽  
Plant Signaling ◽  
Transport Activity ◽  
Calcium Dependent ◽  
Positive Regulator ◽  
Dependent Protein

Abstract Protein kinase-mediated phosphorylation modulates the absorption of many nutrients in plants. CALCIUM-DEPENDENT PROTEIN KINASES (CPKs) are key players in plant signaling to translate calcium signals into diverse physiological responses. However, the regulatory role of CPKs in ammonium uptake remains largely unknown. Here, using methylammonium (MeA) toxicity screening, CPK32 was identified as a positive regulator of ammonium uptake in roots. CPK32 specifically interacted with AMMONIUM TRANSPORTER 1;1 (AMT1;1) and phosphorylated AMT1;1 at the non-conserved serine residue Ser450 in the C-terminal domain. Functional analysis in Xenopus oocytes showed that co-expression of CPK32 and AMT1;1 significantly enhanced the AMT1;1-mediated inward ammonium currents. In transgenic plants, the phosphomimic variant AMT1;1S450E, but not the non-phosphorylatable variant AMT1;1S450A, fully complemented the MeA insensitivity and restored high-affinity 15NH4+ uptake in both amt1;1 and cpk32 mutants. Moreover, in the CPK32 knockout background, AMT1;1 lost its ammonium transport activity entirely. These results indicate that CPK32 is a crucial positive regulator of ammonium uptake in roots and the ammonium transport activity of AMT1;1 is dependent on CPK32-mediated phosphorylation.

Ammonium transport: unifying concepts and unique aspects

2001 ◽  
Vol 28 (9) ◽  
pp. 959 ◽  
Author(s):  
Anne van Dommelen ◽  
René de Mot ◽  
Jos Vanderleyden
Keyword(s):  
Current Knowledge ◽  
Natural Habitat ◽  
Physiological Role ◽  
Ammonium Uptake ◽  
Ammonium Transport ◽  
Symbiotic Interaction ◽  
Ammonium Transporters ◽  
Operating Current ◽  
Living Organisms

This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000 Ammonium uptake by cells has been studied for more than a century, but only recently a family of ammonium transporters (Mep/Amt) with 10–12 transmembrane domains has been defined. These proteins are probably ubiquitous, since homologues have been found in the major kingdoms of living organisms. Plants as well as yeast and some archaebacteria have multiple Mep/Amt paralogues, which can be distinguished by their affinity for ammonium and the ammonium analogue methylammonium. Most ammonium transporters are induced in nitrogen-starving conditions, both in prokaryotes and plants. In Saccharomyces cerevisiae, Escherichia coli and Azospirillum brasilense Mep/Amt proteins where shown to be necessary for growth when the external concentration of the diffusive ammonium form (NH3) becomes limiting. Ammonium transporters also play an important role in pseudohyphal differentiation in yeast and efficient symbiotic interaction between Rhizobium etli and its host plant. In most bacteria, NH4+ transport appears to be a uniport mechanism driven by the membrane potential, but, depending on the organism, a different mode of ammonium uptake may be operating. Current knowledge offers the basis to investigate further the physiological role of ammonium transporters in the natural habitat of organisms and their importance in plant–bacteria interactions.

scholarly journals A twin histidine motif is the core structure for high-affinity substrate selection in plant ammonium transporters

2020 ◽  
Vol 295 (10) ◽  
pp. 3362-3370 ◽  
Author(s):  
Pascal Ganz ◽  
Toyosi Ijato ◽  
Romano Porras-Murrilo ◽  
Nils Stührwohldt ◽  
Uwe Ludewig ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Core Structure ◽  
Ammonium Uptake ◽  
Ammonium Transport ◽  
Substrate Affinity ◽  
Substrate Selection ◽  
Alkali Cations ◽  
High Substrate ◽  
The Core ◽  
Ammonium Transporters

Ammonium transporters (AMT), methylamine permeases (Mep), and the more distantly related rhesus factors (Rh) are trimeric membrane proteins present in all domains of life. AMT/Mep/Rhs are highly selective membrane proteins required for ammonium uptake or release, and they efficiently exclude the similarly sized K+ ion. Previously reported crystal structures have revealed that each transporter subunit contains a unique hydrophobic but occluded central pore, but it is unclear whether the base (NH3) or NH3 coupled with an H+ are transported. Here, using expression of two plant AMTs (AtAMT1;2 and AMT2) in budding yeast, we found that systematic replacements in the conserved twin-histidine motif, a hallmark of most AMT/Mep/Rh, alter substrate recognition, transport capacities, N isotope selection, and selectivity against K+. AMT-specific differences were found for histidine variants. Variants that completely lost ammonium N isotope selection, a feature likely associated with NH4+ deprotonation during passage, substantially transported K+ in addition to NH4+. Of note, the twin-histidine motif was not essential for ammonium transport. However, it conferred key AMT features, such as high substrate affinity and selectivity against alkali cations via an NH4+ deprotonation mechanism. Our findings indicate that the twin-His motif is the core structure responsible for substrate deprotonation and isotopic preferences in AMT pores and that decreased deprotonation capacity is associated with reduced selectivity against K+. We conclude that optimization for ammonium transport in plant AMT represents a compromise between substrate deprotonation for optimal selectivity and high substrate affinity and transport rates.

scholarly journals High-affinity ammonium transport by Arabidopsis thaliana AMT1;4

2021 ◽  
Vol 43 (4) ◽  
Author(s):  
Nino Bindel ◽  
Benjamin Neuhäuser
Keyword(s):  
Arabidopsis Thaliana ◽  
Xenopus Laevis ◽  
Pollen Tube ◽  
Pollen Grains ◽  
Transport Proteins ◽  
Ammonium Transporter ◽  
Ammonium Transport ◽  
High Affinity ◽  
Ammonium Transporters ◽  
Unique Expression Pattern

AbstractIn plants high affinity transport proteins mediate the essential transport of ammonium across membranes. In Arabidopsis thaliana six of these AMmonium Transporters (AMTs) are encoded by the genome. All of them show a unique expression pattern. While most AMTs are highly expressed in the root, AtAMT1;4 expression is limited to the pollen grains and the pollen tube. Here, we addressed the transport characteristics of AtAMT1;4 in the heterologous Xenopus laevis oocytes system. The transport saturated and showed high affinity for ammonium with a Km value lower than 10 µM. Based on our electrophysiological analysis, we classified AtAMT1;4 as a high affinity ammonium transporter.

scholarly journals The Arabidopsis thaliana E3 Ubiquitin Ligase BRIZ Functions in Abscisic Acid Response

2021 ◽  
Vol 12 ◽  
Author(s):  
Katrina J. Linden ◽  
Mon Mandy Hsia ◽  
Yi-Tze Chen ◽  
Judy Callis
Keyword(s):  
Arabidopsis Thaliana ◽  
Abscisic Acid ◽  
E3 Ligase ◽  
Normal Growth ◽  
Growth Conditions ◽  
Aba Signaling ◽  
Wild Type ◽  
Ubiquitin System ◽  
Early Seedling ◽  
Cotyledon Expansion

The ubiquitin system is essential for multiple hormone signaling pathways in plants. Here, we show that the Arabidopsis thaliana E3 ligase BRIZ, a heteromeric ligase that consists minimally of BRIZ1 and BRIZ2 proteins, functions in abscisic acid (ABA) signaling or response. briz1 and briz2 homozygous mutants either fail to germinate or emerge later than wild-type seedlings, with little cotyledon expansion or root elongation and no visible greening. Viability staining indicates that briz1 and briz2 embryos are alive but growth-arrested. Germination of briz mutants is improved by addition of the carotenoid biosynthetic inhibitor fluridone or gibberellic acid (GA3), and briz mutants have improved development in backgrounds deficient in ABA synthesis (gin1-3/aba2) or signaling (abi5-7). Endogenous ABA is not higher in briz2 seeds compared to wild-type seeds, and exogenous ABA does not affect BRIZ mRNAs in imbibed seeds. These results indicate that briz embryos are hypersensitive to ABA and that under normal growth conditions, BRIZ acts to suppress ABA signaling or response. ABA signaling and sugar signaling are linked, and we found that briz1 and briz2 mutants excised from seed coats are hypersensitive to sucrose. Although briz single mutants do not grow to maturity, we were able to generate mature briz2-3 abi5-7 double mutant plants that produced seeds. These seeds are more sensitive to exogenous sugar and are larger than seeds from sibling abi5-7 BRIZ2/briz2-3 plants, suggesting that BRIZ has a parental effect on seed development. From these data, we propose a model in which the BRIZ E3 ligase suppresses ABA responses during seed maturation and germination and early seedling establishment.

scholarly journals Calcium-Dependent Protein Kinase CPK21 Functions in Abiotic Stress Response in Arabidopsis thaliana

2011 ◽  
Vol 4 (1) ◽  
pp. 83-96 ◽  
Author(s):  
Sandra Franz ◽  
Britta Ehlert ◽  
Anja Liese ◽  
Joachim Kurth ◽  
Anne-Claire Cazalé ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Abiotic Stress ◽  
Stress Response ◽  
Protein Kinase ◽  
Abiotic Stress Response ◽  
Dependent Protein Kinase ◽  
Calcium Dependent ◽  
Dependent Protein ◽  
Calcium Dependent Protein Kinase
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