Analysis of the promotors of the single-copy genes for plastocyanin and subunit delta of the chloroplast ATP synthase from spinach

Polymorphism of a new Ty1-copia retrotransposon in durum wheat under salt and light stresses

Long terminal repeat retrotransposons are the most abundant mobile elements in the plant genome and play an important role in the genome reorganization induced by environmental challenges. Their success depends on the ability of their promoters to respond to different signaling pathways that regulate plant adaptation to biotic and abiotic stresses. We have isolated a new Ty1-copia-like retrotransposon, named Ttd1a from the Triticum durum L. genome. To get insight into stress activation pathways in Ttd1a, we investigated the effect of salt and light stresses by RT-PCR and S-SAP profiling. We screened for Ttd1a insertion polymorphisms in plants grown to stress and showed that one new insertion was located near the resistance gene. Our analysis showed that the activation and mobilization of Ttd1a was controlled by salt and light stresses, which strengthened the hypothesis that stress mobilization of this element might play a role in the defense response to environmental stresses.

Contribution of plastocyanin isoforms to photosynthesis and copper homeostasis in Arabidopsis thaliana grown at different copper regimes

In land plants plastocyanin is indispensable and therefore copper (Cu) availability is a prerequisite for growth. When Cu supply is limited, higher plants prioritize the Cu delivery to plastocyanin by down-regulation of other Cu proteins. Arabidopsis has two plastocyanin genes (PETE1 and PETE2). PETE2 is the predominant isoform in soil-grown plants and in hydroponic cultures it is accumulated in response to Cu addition. It functions as a Cu sink when more Cu is available, in addition to its role as an electron carrier. PETE1 is not affected by Cu feeding and it is the isoform that drives electron transport under Cu-deficiency. Cu feeding rescued the defect in photosystem II electron flux (Phi(PSII)) in the pete1 mutant whereas Phi(PSII) was not changed in the pete2 mutant as Cu was added. Plants with mutations in the plastocyanin genes had altered Cu homeostasis. The pete2 mutant accumulated more Cu/Zn superoxide dismutase (CSD2 and CSD1) and Cu chaperone (CCS) whereas the pete1 mutant accumulated less. On the other hand, less iron superoxide dismutase (FeSOD) and microRNA398b were observed in the pete2 mutant, whereas more were accumulated in the pete1 mutant. Our data suggest that plastocyanin isoforms are different in their response to Cu and the absence of either one changes the Cu homeostasis. Also a small amount of plastocyanin is enough to support efficient electron transport and more PETE2 is accumulated as more Cu is added, presumably, to buffer the excess Cu.

Photosynthetic redox regulation of the plastocyanin promoter in tobacco

Persistent light quality gradients in dense plant populations induce imbalances in the distribution of excitation energy between the photosystems. Plants counteract such conditions by re-adjusting the stoichiometry of photosystems, which involves control of photosynthesis gene expression both in chloroplasts and in the nucleus. Decisive control parameters are redox signals from the photosynthetic electron transport chain, one prominent is the plastoquinone (PQ) pool. In a recent study, a plastocyanin (PC)-promoter::beta-glucuronidase reporter gene construct in tobacco demonstrated reversible redox regulation in response to varying light qualities. Here, northern and Western analyses demonstrate that this promoter regulation also accounts for the accumulation of the endogenous tobacco PetE gene transcripts and the protein amounts of the encoded PC. Hence, the reporter gene construct reflects the natural regulation of this nuclear gene in tobacco. In kinetic experiments, the response of the construct to either oxidation or reduction of the PQ pool was tested by defined light quality shifts. The construct displayed upregulation in response to a reduction signal and downregulation in response to an oxidation signal, both with a half-time of about 24 h. The response was finished after 48 h. DCMU application abolished the upregulation in response to the reduction signal, indicating the dependence on thylakoid membrane electron transport. To study the redox-responsive promoter region in more detail, several promoter deletion constructs were tested for their responsiveness. All constructs displayed a reversible response to light-induced oxidation and reduction signals; however, a minimal promoter region localised between -168 to -79 bp upstream of the transcription start site was sufficient to confer this redox regulation. This indicates that photosynthetic redox signals act on distinct regions in the PC promoter in a manner independent from photoreceptors and upstream cis elements conferring high basic expression in the light.

Light and plastid signals regulate the expression of the pea plastocyanin gene through a common region at the 5' end of the coding region

Expression of the pea plastocyanin gene (PetE) is regulated by light and plastid signals. Previous work indicated that light and plastid regulation of pea PetE operates post-transcriptionally in transgenic tobacco, and requires the correct 5' terminus of the PetE transcript and the PetE-coding region. The post-transcriptional light and plastid regulation of pea PetE has now been demonstrated to operate in transgenic Arabidopsis, where in contrast the endogenous PETE gene is regulated transcriptionally. Transgenic tobacco seedlings containing constructs with progressive 3' deletions of the PetE-coding region fused to the luciferase (Luc) reporter gene demonstrate that the first 60 nucleotides of the coding region are sufficient for regulated accumulation of Luc transcripts by light and plastid signalling pathways affected by treatment with norflurazon and lincomycin. PetE constructs containing premature stop codons were generated to investigate whether translation has a role in light or plastid regulation. Insertion of a stop codon in place of the second codon of the PetE-coding region diminished both light and plastid regulation of PetE transcripts, whereas stop codons inserted later in the transcript had no effect on light or plastid regulation. These experiments indicate that the 5' end of the plastocyanin-coding region contains sequences important for regulation by light and plastid signals.

The promoter from the rice nuclear gene encoding chloroplast aldolase confers mesophyll-specific and light-regulated expression in transgenic tobacco

The rice genome contains at least four separate loci that encode aldolase isozymes. Among these, the aldolase P (AldP) gene, a nuclear gene coding for chloroplast aldolase, is expressed predominantly in the leaf blade mesophyll cells in rice. To dissect promoter elements that regulate such tissue- or cell type-specific expression, we constructed various AldP promoter-beta-glucuronidase (GUS) fusion genes and transferred them into Nicotiana tabacum (tobacco) plants. Analysis of GUS activities in the transgenic tobacco revealed the presence of at least two elements within 2.0 kb AldP promoter region. One is located within the segment from position -2.0 kb to -1.2 kb and acts as a negative element. The other is a positive element located between -1.2 kb and -0.31 kb that confers developmentally regulated, mesophyll cell-specific expression. In addition, the 1.2 kb rice promoter segment flanking the transcription start site contains an element(s) that serves as target for light induction in tobacco. The results suggest that the AldP gene promoter of rice, a monocot promoter, can function in an essentially physiological manner in the dicot tobacco plant.

The steady-state mRNA levels for thylakoid proteins exhibit coordinate diurnal regulation

Steady-state mRNA levels for thylakoid proteins were analysed in spinach cotyledons under diurnally changing light conditions. Most fluctuate considerably throughout the day, while the levels of others show only low amplitude or no oscillation. Levels of mRNAs coding for proteins that belong to the same multiprotein complex generally oscillate in parallel and exhibit maxima that are specific for that complex: mRNAs for photosystem I proteins appear prior to those for photosystem II polypeptides and these again prior to mRNAs for the three polypeptides constituting the oxygen-evolving complex. For the mRNAs that change with high amplitudes (e.g. those for LHCP or the 20 kDa apoprotein of the CP24 complex) oscillations have also been found under constant conditions, indicating that a circadian oscillator is involved. Transgenic tobacco seedlings harbouring chimeric GUS gene fusions with 5'-flanking sequences from the spinach genes Lhcb, PsaF and AtpD (encoding a light-harvesting chlorophyll a/b apoprotein of photosystem II, subunit 3 of photosystem I and subunit delta of the plastid ATP synthase, respectively) confirm that the differences in the amplitudes as well as the timepoints of maximum mRNA accumulation are perceived via cis-regulatory elements upstream of the respective ATG codons.

Structure and characterization of the gene encoding the ferredoxin-NADP reductase-binding protein from Zea mays L

A genomic clone encoding ferredoxin-NADP reductase binding protein (BP) from Zea mays L. was sequenced and characterized. The promoter region (692 bp) shows several motives resembling those involved in enhancement, tissue-specific expression and light regulation in plants, besides the typical TATA and CAAT boxes. The coding sequence is interrupted by two introns. The deduced amino acid (aa) sequence corresponds to 22.85 kDa for the precursor polypeptide, including a transit peptide of 64 aa and a mature protein of 148 aa.

Interacting cis elements in the plastocyanin promoter from spinach ensure regulated high-level expression

The spinach plastocyanin promoter contains most, if not all, cis elements crucial for its activity downstream of -259 bp relative to the transcription start site. The -259/-79 bp promoter fragment is capable of conferring glucuronidase (GUS) gene expression on the minimal -90/+3 bp 35S RNA promoter of CaMV and -51/+60 bp plastocyanin promoter, regardless of its orientation. Using 5' promoter deletion analysis and site directed mutagenesis we identified three regions, designated PC-1 (-195/-188), PC-2 (-179/-164) and PC-3 (-90/-77) for promoter function. An interaction between PC-3 and the upstream elements is required for high levels of expression. All these sequences contain binding sites for protein factors, as shown by gel shift assays. PC-3 includes a binding site with some resemblance to GT-1 box II, but additional nucleotide sequences immediately downstream of this motif, which are conserved among all published plastocyanin promoters, are required as well. The sequence interval -168/-79 bp is sufficient to confer light-responsive, organ-specific and chloroplast-dependent GUS gene expression on minimal promoters.

Activity of the promoter of the Lhca3.St.1 gene, encoding the potato apoprotein 2 of the light-harvesting complex of Photosystem I, in transgenic potato and tobacco plants

We have isolated cDNA and genomic clones for the potato (Solanum tuberosum) apoprotein 2 of the light harvesting complex of Photosystem I, designated Lhca3.St.1. The protein shows all characteristics of the family of chlorophyll a/b-binding proteins. Potato Lhca3.1 gene expression occurs predominantly in leaves, and is transcriptionally regulated by light. One gene copy is present per haploid genome. The sequence of the 5' upstream region was determined. Most boxes identified in the promoter sequences of genes whose expression is light-regulated recur in the Lhca3.St.1 sequence. Functional analyses of the Lhca3.St.1 promoter and two deletion derivatives in transgenic potato transformed with a promoter-GUS fusion show high promoter activity in leaves and other green parts of the plant, which depends on light. Activity is absent in roots and potato tubers. The 500 bp promoter fragment is as active as the full 2.0 kb sequence, showing that all regulatory elements are present on the smallest deletion derivative. In transgenic tobacco (Nicotiana tabacum) plants carrying the largest promoter derivative a similar distribution of activity is found. Promoter activity is not restricted to the phloem, but also prominent in the xylem of the young stem, which contrasts with promoters of other photosynthesis-associated genes.

In vitro binding of nuclear proteins to the barley plastocyanin gene promoter region

Plastocyanin is a nuclear-encoded chloroplast protein participating in electron transport during photosynthesis. The plastocyanin gene is expressed in photosynthetic tissue in a developmentally regulated manner and the expression is stimulated by light. A genomic clone encoding the plastocyanin precursor was isolated from a barley (Hordeum vulgare) lambda library using a barley cDNA clone as a probe and the sequence of a 1.9-kb DNA fragment containing the plastocyanin gene was determined. TATA and CCAAT boxes are located 34-bp and 68-bp, respectively, upstream of the transcription start site, the 5'-untranslated leader is 78 nucleotides long, and the intronless gene has at least two different polyadenylation sites. DNA sites in the plastocyanin gene that mediate binding of barley nuclear proteins were mapped by mobility-shift assays with fragments of the promoter/upstream region. Two of the three specific binding sites characterised in more detail were found to form complexes with the same factor in cross-competition experiments. One of these sites, narrowed down to a 17-bp sequence at position -512, contains the consensus binding site for Myb-like transcription factors. The third specific binding site, located at position -622, contains the sequence CACGTG which is a high-affinity-binding site for transcription factors of the basic-region leucine-zipper family.

The pea plastocyanin promoter directs cell-specific but not full light-regulated expression in transgenic tobacco plants

A series of 5' deletions of the pea plastocyanin gene (petE) promoter fused to the beta-glucuronidase (GUS) reporter gene has been examined for expression in transgenic tobacco plants. Strong positive and negative cis-elements which modulate quantitative expression of the transgene in the light and the dark have been detected within the petE promoter. Disruption of a negative regulatory element at -784 bp produced the strongest photosynthesis-gene promoter so far described. Histochemical analysis demonstrated that all petE-GUS constructs directed expression in chloroplast-containing cells, and that a region from -176 bp to +4 bp from the translation start site was sufficient for such cell-specific expression. The petE-promoter fusions were expressed at high levels in etiolated transgenic tobacco seedlings but there was no marked induction of GUS activity in the light. The endogenous tobacco plastocyanin genes and the complete pea plastocyanin gene in transgenic tobacco plants were also expressed in the dark, but showed a three- to sevenfold increase in the light. This indicates a requirement for sequences 3' to the promoter for the full light response of the petE gene.

Characterization of the promoter from the single-copy gene encoding ferredoxin-NADP(+)-oxidoreductase from spinach

We describe a genomic DNA segment from spinach that bears part of the single-copy gene for ferredoxin-NADP(+)-oxidoreductase (FNR) including a 3.4 kb promoter sequence. Dissection of this DNA segment and its analysis in GUS (beta-glucuronidase) gene fusions in transgenic tobacco demonstrated that the promoter differs in structure from all other promoters for thylakoid protein genes studied to date. Two regions with light-responsive elements were identified. One is located within the first 118 bp upstream of the transcription initiation site. A second fragment covering nucleotide positions -220 to -119 is capable of conferring light-dependent GUS gene expression on two different minimal promoters. The latter fragment binds a transacting factor in gel-shift assays. None of the fragments carries cis elements known from other genes to be involved in light-controlled expression. Comparison of the light responsiveness of GUS gene fusions controlled by the -753/+231 and -118/+231 regions indicates that they respond differentially to phytochrome-dependent signals and that their expression in tobacco is not restricted to tissue with functional chloroplasts.

Import and processing of the precursor of the delta subunit of tobacco chloroplast ATP synthase

A cDNA clone encoding the complete precursor of the delta subunit of chloroplast ATP synthase has been isolated from a tobacco (Nicotiana tabacum) leaf cDNA library in lambda gt11. The 880 bp insert encodes a polypeptide of 248 amino acid residues, of which 61 residues constitute an N-terminal presequence and 187 residues make up the mature delta subunit. Transcription and translation of the cDNA in vitro produced a protein of 29 kDa which was imported by isolated pea chloroplasts and processed to the mature 20 kDa subunit. The delta subunit precursor was processed to the mature size by a processing peptidase present in pea stromal extracts. Hybridisation of the cDNA to Southern blots of tobacco genomic DNA suggests the presence of two genes in the haploid genome.

Import and processing of the precursor form of the gamma subunit of the chloroplast ATP synthase from tobacco

A cDNA clone encoding the complete precursor of the gamma subunit of chloroplast ATP synthase has been isolated from a tobacco (Nicotiana tabacum) leaf cDNA library in lambda gt11. The 1.4 kb insert encodes a polypeptide of 377 amino acid residues, of which 55 residues constitute an N-terminal presequence and 322 residues make up the mature gamma subunit. Hybridisation of the cDNA to Southern blots of tobacco genomic DNA indicates the presence of two genes in the haploid genome. Transcription and translation of the cDNA in vitro produced a protein of 41 kDa which was imported by isolated pea chloroplasts and processed to the mature 36 kDa subunit. The gamma subunit precursor was processed to the mature size by a processing peptidase of 180 kDa present in pea stromal extracts.