A probable Na
 +
 (K
 +
 )/H
 +
 exchanger on the chloroplast envelope functions in pH homeostasis and chloroplast development in
 Arabidopsis thaliana

Song, Chun‐Peng; Guo, Yan; Qiu, Quan‐Sheng; Lambert, Georgina M.; Galbraith, David W.; Jagendorf, André T.; Zhu, Jian Kang

doi:10.1073/pnas.0403709101

Cited by 108 publications

(75 citation statements)

References 33 publications

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“…Such a non-enzymatic NO production from nitrite has in particular been reported to occur at acidic pH in the apoplasm for example (52) and could explain the NO effects on germinating seeds (52)(53)(54). However, such a nitrite-dependent NO production is unlikely to occur in the stroma of plastids where the pH value is 7.0 or higher (55,56).…”

Section: Discussionmentioning

confidence: 93%

An Iron-induced Nitric Oxide Burst Precedes Ubiquitin-dependent Protein Degradation for Arabidopsis AtFer1 Ferritin Gene Expression

Arnaud

Murgia²,

Boucherez³

et al. 2006

Journal of Biological Chemistry

170

109

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Ferritins play an essential role in iron homeostasis by sequestering iron in a bioavailable and non-toxic form. In plants, ferritin mRNAs are highly and quickly accumulated in response to iron overload. Such accumulation leads to a subsequent ferritin protein synthesis and iron storage, thus avoiding oxidative stress to take place. By combining pharmacological and imaging approaches in an Arabidopsis cell culture system, we have identified several elements in the signal transduction pathway leading to the increase of AtFer1 transcript level after iron treatment. Nitric oxide quickly accumulates in the plastids after iron treatment. This compound acts downstream of iron and upstream of a PP2A-type phosphatase to promote an increase of AtFer1 mRNA level. The AtFer1 gene transcription has been previously shown to be repressed under low iron conditions with the involvement of the cis-acting element iron-dependent regulatory sequence identified within the AtFer1 promoter sequence. We show here that the repressor is unlikely a transcription factor directly bound to the iron-dependent regulatory sequence; such a repressor is ubiquitinated upon iron treatment and subsequently degraded through a 26 S proteasome-dependent pathway.As the major cofactor of proteins involved in essential processes like photosynthesis, respiration, DNA replication, or nitrogen fixation, iron is an essential element for life. Nonetheless, in the free ionic form, iron is toxic as it can catalyze the formation of reactive oxygen species through the Fenton reaction. These reactive oxygen species damage the cell membranes, DNA, and proteins (1, 2). Thus, iron homeostasis has to be tightly regulated, to avoid starvation that impairs the metabolism, and to avoid excess that may lead to cell death. Iron homeostasis is strongly dependent on ferritins, which are ironstorage proteins, found in bacteria, animals, and plants. Plant and animal ferritin structures are very similar, and are formed by 24 subunits arranged to form a hollow sphere able to sequester iron in a non-toxic and bioavailable form (3).In animals, ferritin synthesis is mainly regulated at the posttranscriptional level (3, 4). Ferritin mRNAs contain iron-responsive elements in their 5Ј-untranslated regions that function as binding sites for two related trans-acting factors, namely iron regulatory proteins IRP1 and IRP2. When bound to the iron-responsive element in the ferritin mRNA, the IRP inhibit translation of the transcript (4). IRP1 is a bifunctional protein that when iron is abundant possesses a 4Fe-4S cluster and acts as cytoplasmic aconitase. When iron levels are low, the 4Fe-4S cluster disassembles and the apoprotein acquires IRP 3 activity, thus repressing ferritin translation. High levels of iron lead to the 4Fe-4S cluster reconstitution and therefore the protein aconitase activity. In contrast to IRP1, IRP2 cannot assemble a iron-sulfur cluster and lacks aconitase activity. IRP2 shares about 60% amino acid sequence identity with IRP1, but differs only in having a 73-amino aci...

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Section: Discussionmentioning

confidence: 93%

An Iron-induced Nitric Oxide Burst Precedes Ubiquitin-dependent Protein Degradation for Arabidopsis AtFer1 Ferritin Gene Expression

Arnaud

Murgia²,

Boucherez³

et al. 2006

Journal of Biological Chemistry

170

109

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“…4B , then its inward electrochemical gradient would be considerably less when the stroma and external solution have the same pH than when the stroma is more alkaline than the external solution. Alkalinization of the stroma may occur via Na + /H + exchange, as this transport process has been reported to play an important role in the homeostasis of cytosolic and stromal pH (Song et al, 2004).…”

Section: Discussionmentioning

confidence: 99%

The Sink-Specific Plastidic Phosphate Transporter PHT4;2 Influences Starch Accumulation and Leaf Size in Arabidopsis

et al. 2011

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Nonphotosynthetic plastids are important sites for the biosynthesis of starch, fatty acids, and amino acids. The uptake and subsequent use of cytosolic ATP to fuel these and other anabolic processes would lead to the accumulation of inorganic phosphate (Pi) if not balanced by a Pi export activity. However, the identity of the transporter(s) responsible for Pi export is unclear. The plastid-localized Pi transporter PHT4;2 of Arabidopsis (Arabidopsis thaliana) is expressed in multiple sink organs but is nearly restricted to roots during vegetative growth. We identified and used pht4;2 null mutants to confirm that PHT4;2 contributes to Pi transport in isolated root plastids. Starch accumulation was limited in pht4;2 roots, which is consistent with the inhibition of starch synthesis by excess Pi as a result of a defect in Pi export. Reduced starch accumulation in leaves and altered expression patterns for starch synthesis genes and other plastid transporter genes suggest metabolic adaptation to the defect in roots. Moreover, pht4;2 rosettes, but not roots, were significantly larger than those of the wild type, with 40% greater leaf area and twice the biomass when plants were grown with a short (8-h) photoperiod. Increased cell proliferation accounted for the larger leaf size and biomass, as no changes were detected in mature cell size, specific leaf area, or relative photosynthetic electron transport activity. These data suggest novel signaling between roots and leaves that contributes to the regulation of leaf size.

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“…There is a 1:1 relationship between short-circuit current and K + fluxes, which suggests primary active transport of K + , which would be electrogenic and could generate this positive potential. It is, however, difficult to distinguish between primary active inward transport of K + and an inward H + pump with tightly coupled K + /H + antiport, as has been postulated for the chloroplast envelope (Song et al, 2004). The vacuolar pH is 5.8 in the light, producing a E H across the tonoplast of )180 mV, assuming cytoplasmic pH is 7.5 (Davis, 1981).…”

Section: Electrophysiologymentioning

confidence: 99%

Electrophysiology of Turgor Regulation in Marine Siphonous Green Algae

2006

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Abstract. We review electrophysiological measures of turgor regulation in some siphonous green algae, primarily the giant-celled marine algae, Valonia, and Ventricaria, with particular comparison to the well studied charophyte algae Chara and Lamprothamnium. The siphonous green algae have a less negative plasma membrane potential, and are unlikely to have a proton-based chemiosmotic transport system, dominated by active electrogenic K + uptake. We also make note of the unusual cellular structure of the siphonous green algae. Hypertonic stress, due to increased external osmotic pressure, is accompanied by positive-going potential difference (PD), increase in conductance, and slow turgor-regulation. The relationship between these is not yet resolved, but may involve changes in K + conductance (G K ) or active K + transport at both membranes. Hypotonic turgor regulation, in response to decrease external osmotic pressure, is 3 times faster than hypertonic turgor regulation. It is accompanied by a negative-going PD, although conductance also increases. The conductance increase and the magnitude of the PD change are strongly correlated with the magnitude of hypotonic stress.

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A probable Na ⁺ (K ⁺ )/H ⁺ exchanger on the chloroplast envelope functions in pH homeostasis and chloroplast development in Arabidopsis thaliana

Cited by 108 publications

References 33 publications

An Iron-induced Nitric Oxide Burst Precedes Ubiquitin-dependent Protein Degradation for Arabidopsis AtFer1 Ferritin Gene Expression

An Iron-induced Nitric Oxide Burst Precedes Ubiquitin-dependent Protein Degradation for Arabidopsis AtFer1 Ferritin Gene Expression

The Sink-Specific Plastidic Phosphate Transporter PHT4;2 Influences Starch Accumulation and Leaf Size in Arabidopsis

Electrophysiology of Turgor Regulation in Marine Siphonous Green Algae

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A probable Na + (K + )/H + exchanger on the chloroplast envelope functions in pH homeostasis and chloroplast development in Arabidopsis thaliana

Cited by 108 publications

References 33 publications

An Iron-induced Nitric Oxide Burst Precedes Ubiquitin-dependent Protein Degradation for Arabidopsis AtFer1 Ferritin Gene Expression

An Iron-induced Nitric Oxide Burst Precedes Ubiquitin-dependent Protein Degradation for Arabidopsis AtFer1 Ferritin Gene Expression

The Sink-Specific Plastidic Phosphate Transporter PHT4;2 Influences Starch Accumulation and Leaf Size in Arabidopsis

Electrophysiology of Turgor Regulation in Marine Siphonous Green Algae

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A probable Na ⁺ (K ⁺ )/H ⁺ exchanger on the chloroplast envelope functions in pH homeostasis and chloroplast development in Arabidopsis thaliana