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1.
Nat Commun ; 8: 15300, 2017 05 15.
Article in English | MEDLINE | ID: mdl-28504266

ABSTRACT

Environmental cues profoundly modulate cell proliferation and cell elongation to inform and direct plant growth and development. External phosphate (Pi) limitation inhibits primary root growth in many plant species. However, the underlying Pi sensory mechanisms are unknown. Here we genetically uncouple two Pi sensing pathways in the root apex of Arabidopsis thaliana. First, the rapid inhibition of cell elongation in the transition zone is controlled by transcription factor STOP1, by its direct target, ALMT1, encoding a malate channel, and by ferroxidase LPR1, which together mediate Fe and peroxidase-dependent cell wall stiffening. Second, during the subsequent slow inhibition of cell proliferation in the apical meristem, which is mediated by LPR1-dependent, but largely STOP1-ALMT1-independent, Fe and callose accumulate in the stem cell niche, leading to meristem reduction. Our work uncovers STOP1 and ALMT1 as a signalling pathway of low Pi availability and exuded malate as an unexpected apoplastic inhibitor of root cell wall expansion.


Subject(s)
Arabidopsis Proteins/metabolism , Organic Anion Transporters/metabolism , Phosphates/metabolism , Plant Roots/metabolism , Transcription Factors/metabolism , Arabidopsis/genetics , Arabidopsis/metabolism , Arabidopsis Proteins/genetics , Cell Enlargement , Cell Wall/genetics , Cell Wall/metabolism , Gene Expression Regulation, Plant , Iron/metabolism , Malates/metabolism , Meristem/cytology , Meristem/genetics , Meristem/metabolism , Organic Anion Transporters/genetics , Oxidoreductases/genetics , Oxidoreductases/metabolism , Peroxidase/genetics , Peroxidase/metabolism , Plant Roots/cytology , Plant Roots/genetics , Plants, Genetically Modified , Signal Transduction/genetics , Transcription Factors/genetics
2.
Plant Physiol ; 161(1): 508-20, 2013 Jan.
Article in English | MEDLINE | ID: mdl-23151348

ABSTRACT

In addition to the linear electron flow, a cyclic electron flow (CEF) around photosystem I occurs in chloroplasts. In CEF, electrons flow back from the donor site of photosystem I to the plastoquinone pool via two main routes: one that involves the Proton Gradient Regulation5 (PGR5)/PGRL1 complex (PGR) and one that is dependent of the NADH dehydrogenase-like complex. While the importance of CEF in photosynthesis and photoprotection has been clearly established, little is known about its regulation. We worked on the assumption of a redox regulation and surveyed the putative role of chloroplastic thioredoxins (TRX). Using Arabidopsis (Arabidopsis thaliana) mutants lacking different TRX isoforms, we demonstrated in vivo that TRXm4 specifically plays a role in the down-regulation of the NADH dehydrogenase-like complex-dependent plastoquinone reduction pathway. This result was confirmed in tobacco (Nicotiana tabacum) plants overexpressing the TRXm4 orthologous gene. In vitro assays performed with isolated chloroplasts and purified TRXm4 indicated that TRXm4 negatively controls the PGR pathway as well. The physiological significance of this regulation was investigated under steady-state photosynthesis and in the pgr5 mutant background. Lack of TRXm4 reversed the growth phenotype of the pgr5 mutant, but it did not compensate for the impaired photosynthesis and photoinhibition sensitivity. This suggests that the physiological role of TRXm4 occurs in vivo via a mechanism distinct from direct up-regulation of CEF.


Subject(s)
Arabidopsis/metabolism , Photosynthesis , Photosystem I Protein Complex/metabolism , Thioredoxins/metabolism , Arabidopsis/genetics , Arabidopsis/physiology , Arabidopsis/radiation effects , Arabidopsis Proteins/metabolism , Chlorophyll/metabolism , Chloroplast Proteins/genetics , Chloroplast Proteins/metabolism , Chloroplasts/metabolism , Electron Transport , Enzyme Activation , Ethylmaleimide/pharmacology , Gene Expression Regulation, Enzymologic , Gene Expression Regulation, Plant , Genes, Plant , Light , Mutagenesis, Insertional , NADH Dehydrogenase/metabolism , Oxidation-Reduction , Photosynthetic Reaction Center Complex Proteins/metabolism , Photosystem I Protein Complex/genetics , Plant Leaves/genetics , Plant Leaves/metabolism , Plant Leaves/radiation effects , Plants, Genetically Modified/genetics , Plants, Genetically Modified/metabolism , Plants, Genetically Modified/radiation effects , Plastoquinone/metabolism , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Thioredoxins/genetics , Nicotiana/genetics , Nicotiana/metabolism
3.
Plant Cell Environ ; 30(5): 617-29, 2007 May.
Article in English | MEDLINE | ID: mdl-17407539

ABSTRACT

Carbonic anhydrases (CAs) are Zn-containing metalloenzymes that catalyse the reversible hydration of CO(2). We investigated the alphaCA and betaCA families in Arabidopsis, which contain eight alphaCA (At alphaCA1-8) and six betaCA genes (At betaCA1-6). Analyses of expressed sequence tags (ESTs) from The Arabidopsis Information Resource (TAIR) database indicate that all the betaCA encoding sequences, but only three of the At alphaCA, are expressed. Using semi-quantitative PCR experiments, functional CA genes were more strongly expressed in green tissue, but strong expression was also found in roots for betaCA3, betaCA6 and alphaCA2. Two alphaCA genes were shown to respond to the CO(2) environment, while the others were unresponsive. Using the green fluorescent reporter protein gene fused with cDNA sequences coding for betaCAs, we provided evidence that betaCAs were targeted to specific subcellular compartments: betaCA1 and betaCA5 were targeted to the chloroplast, betaCA2 and betaCA3 to the cytosol, betaCA4 to the plasma membrane and betaCA6 to the mitochondria. The targeting and the pattern of gene expression suggest that CA isoforms play specific roles in subcellular compartments, tissues and organs. The data indicate that other CA isoforms than the well-characterized betaCA1 may contribute to the CO(2) transfer in the cell to the catalytic site of ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco).


Subject(s)
Arabidopsis/genetics , Carbonic Anhydrases/genetics , Amino Acid Sequence , Arabidopsis/enzymology , Arabidopsis/physiology , Carbon Dioxide/physiology , Gene Expression , Molecular Sequence Data , Multigene Family , RNA, Messenger/metabolism , Sequence Analysis, DNA
4.
Plant Cell ; 17(1): 219-32, 2005 Jan.
Article in English | MEDLINE | ID: mdl-15608332

ABSTRACT

In higher plants, the Ndh complex reduces plastoquinones and is involved in cyclic electron flow around photosystem I, supplying extra-ATP for photosynthesis, particularly under environmental stress conditions. Based on plastid genome sequences, the Ndh complex would contain 11 subunits (NDH-A to -K), but homologies with bacterial complex indicate the probable existence of additional subunits. To identify missing subunits, tobacco (Nicotiana tabacum) NDH-H was His tagged at its N terminus using plastid transformation. A functional Ndh subcomplex was purified by Ni(2+) affinity chromatography and its subunit composition analyzed by mass spectrometry. Five plastid encoded subunits (NDH-A, -H, -I, -J, and -K) were identified as well as three new subunits (NDH-M, -N, and -O) homologous to cyanobacterial and higher plant proteins. Arabidopsis thaliana mutants missing one of these new subunits lack a functional Ndh complex, and NDH-M and NDH-N are not detected in a tobacco transformant lacking the Ndh complex. We discuss the involvement of these three nuclear-encoded subunits in the functional integrity of the plastidial complex.


Subject(s)
Cell Nucleus/genetics , Genes, Plant/genetics , NADPH Dehydrogenase/metabolism , Plant Proteins/metabolism , Plastids/metabolism , Protein Subunits/metabolism , Amino Acid Sequence , Arabidopsis/genetics , Arabidopsis/metabolism , Electron Transport Chain Complex Proteins/genetics , Electron Transport Chain Complex Proteins/metabolism , Gene Expression Regulation, Plant/genetics , Molecular Sequence Data , Mutation/genetics , NADPH Dehydrogenase/genetics , Photosynthesis/genetics , Photosystem I Protein Complex/genetics , Photosystem I Protein Complex/metabolism , Plant Proteins/genetics , Plastids/genetics , Protein Subunits/genetics , Thylakoids/genetics , Thylakoids/metabolism , Nicotiana/genetics , Nicotiana/metabolism
5.
Plant Biotechnol J ; 2(5): 389-99, 2004 Sep.
Article in English | MEDLINE | ID: mdl-17168886

ABSTRACT

Rubisco is a hexadecameric enzyme composed of two subunits: a small subunit (SSU) encoded by a nuclear gene (rbcS), and a large subunit (LSU) encoded by a plastid gene (rbcL). Due to its high abundance, Rubisco represents an interesting target to express peptides or small proteins as fusion products at high levels. In an attempt to modify the plant metal content, a polyhistidine sequence was fused to Rubisco, the most abundant protein of plants. Plastid transformation was used to express a polyhistidine (6x) fused to the C-terminal extremity of the tobacco LSU. Transplastomic tobacco plants were generated by cotransformation of polyethylene glycol-treated protoplasts using two vectors: one containing the 16SrDNA marker gene, conferring spectinomycin resistance, and the other the polyhistidine-tagged rbcL gene. Homoplasmic plants containing L8-(His)6S8 as a single enzyme species were obtained. These plants contained normal Rubisco amounts and activity and displayed normal photosynthetic properties and growth. Interestingly, transplastomic plants accumulated higher zinc amounts than the wild-type when grown on zinc-enriched media. The highest zinc increase observed exceeded the estimated chelating ability of the polyhistidine sequence, indicating a perturbation in intracellular zinc homeostasis. We discuss the possibility of using Rubisco to express foreign peptides as fusion products and to confer new properties to higher plants.

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