| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
First published online April 20, 2004; 10.1105/tpc.019729 © 2004 American Society of Plant Biologists cis-Regulatory Elements for Mesophyll-Specific Gene Expression in the C4 Plant Flaveria trinervia, the Promoter of the C4 Phosphoenolpyruvate Carboxylase GeneHeinrich-Heine-Universität, Institut für Entwicklungs und Molekularbiologie der Pflanzen, 40225 Düsseldorf, Germany 1 To whom correspondence should be addressed. E-mail west{at}uni-duesseldorf.de; fax 49-211-81-14871.
C4 photosynthesis depends on the strict compartmentalization of CO2 assimilatory enzymes. cis-regulatory mechanisms are described that ensure mesophyll-specific expression of the gene encoding the C4 isoform of phosphoenolpyruvate carboxylase (ppcA1) of the C4 dicot Flaveria trinervia. To elucidate and understand the anatomy of the C4 ppcA1 promoter, detailed promoter/reporter gene studies were performed in the closely related C4 species F. bidentis, revealing that the C4 promoter contains two regions, a proximal segment up to –570 and a distal part from –1566 to –2141, which are necessary but also sufficient for high mesophyll-specific expression of the ß-glucuronidase reporter gene. The distal region behaves as an enhancer-like expression module that can direct mesophyll-specific expression when inserted into the ppcA1 promoter of the C3 plant F. pringlei. Mesophyll expression determinants were restricted to a 41-bp segment, referred to as mesophyll expression module 1 (Mem1). Evolutionary and functional studies identified the tetranucleotide sequence CACT as a key component of Mem1.
C4 plants are characterized by high rates of photosynthesis as well as an efficient use of water and nitrogen resources. This is because of their unique mode of carbon assimilation that concentrates CO2 at the site of ribulose bisphosphate carboxylase/oxygenase. The functioning of C4 photosynthesis is dependent upon the strict compartmentation of the CO2 assimilatory enzymes into two distinct cell types, mesophyll and bundle-sheath cells. The primary carboxylating enzyme, phosphoenolpyruvate carboxylase, accumulates exclusively in the mesophyll cells, and the secondary carboxylase, ribulose bisphosphate carboxylase/oxygenase, and the decarboxylating enzymes, such as NADP-dependent malic enzyme, are restricted to the bundle-sheath cells (Hatch, 1987  ).
This division of labor between mesophyll and bundle-sheath cells is the result of differential gene expression. In NADP-malic enzyme-type C4 species, for instance, transcripts for phosphoenolpyruvate carboxylase, pyruvate phosphate dikinase, NADP-malic enzyme, and the small subunit of ribulose bisphosphate carboxylase/oxygenase, accumulate differentially in the two cell types. This differential accumulation is largely because of transcriptional control (Sheen, 1999
C4 plants occur in at least 18 families of monocotyledonous and dicotyledonous plants. This indicates that C4 plants must have evolved several times independently from C3 ancestors during the evolution of angiosperms (Kellogg, 1999
As a starting point to understanding the molecular basis of the evolution of C4 genes, we are focusing on the C4 gene for PEPC and are using the genus Flaveria (Asteraceae) (Powell, 1978
Three major changes must have occurred during C3-to-C4 evolution to transform a C3 PEPC gene into a C4 gene (reviewed in Westhoff and Gowik, 2004
The C4 PEPCs of C4 Flaveria species are encoded by the phosphoenolpyruvate carboxylase A (ppcA) gene class (Hermans and Westhoff, 1992
Analysis of ppcA1 promoter/ß-glucuronidase (GUS) reporter gene fusions in the C4 plant F. bidentis revealed that the ppcA1 promoter of F. trinervia directs high levels of reporter gene expression in the mesophyll cells (Stockhaus et al., 1997 To fully understand the anatomy of the C4 ppcA1 promoter and to identify the cis-regulatory elements that are essential for its mesophyll specificity, detailed promoter reporter gene analyses with transgenic F. bidentis were performed. These experiments revealed that the C4 promoter contains two regions, a proximal region up to –570 (PR) and a distal region from –1566 to –2141 (DR), which are necessary and sufficient for a high mesophyll-specific expression. The DR behaves as an enhancer-like expression module and is able to confer a mesophyll expression component to the ppcA1 promoter of F. pringlei. Further dissection of the DR identified a 41-bp module (mesophyll expression module 1 [Mem1]) that in conjunction with the PR, is sufficient for mesophyll-specific expression. Evolutionary and functional analyses identified the tetranucleotide CACT as a key element of Mem1.
The Distal Segment of the C4 ppcA1 Promoter Is Required for both Expression Specificity and Quantity and Behaves as an Enhancer-Like Expression Module In the C3 plant tobacco (Nicotiana tabacum), the C4 ppcA1 promoter behaved essentially as a palisade parenchyma–specific promoter. The expression in the palisade parenchyma was lost when the 5' distal 1618 bp of 5' distal sequences were removed and the remaining 570 bp of proximal sequences were analyzed for promoter activity (Stockhaus et al., 1994 ). This finding suggested that the 5' DR of the promoter contains cis-regulatory elements that are absolutely essential for a high level of expression and for mesophyll specificity. To define this distal promoter region precisely, a systematic deletion analysis was performed using the high level of expression in the palisade parenchyma cells of the C3 plant tobacco as a test system. When the ppcA1 starting promoter of 2188 bp (named ppcA-LFt; Figure 1) was shortened by 623 bp (construct ppcA-1,5Ft; Figure 2A), the expression activity was almost entirely lost. It is highly significant that no palisade parenchyma expression was detected by histochemical staining (data not shown). Further deletion of 5' promoter sequences (construct ppcA-1,0Ft; Figure 2A) influenced the resulting promoter activity as compared with the ppcA-1,5Ft promoter construct only marginally (Figure 2B). Both the ppcA-1,5Ft and ppcA-1,0Ft constructs showed a lower promoter activity than the ppcA-PRFt promoter fragment (Figures 2A and 2B). These observations suggested that the region between base pairs –570 and –1565 appears to contain sequences that reduce promoter activity but that the DR between base pairs –1565 and –2188 is absolutely essential for the C4 ppcA1 promoter activity in tobacco.
This fact was tested directly by fusing the distal part between base pairs –1566 and –2141 in direct and inverse orientation with the proximal –570 bp of promoter sequences (constructs ppcA-PRFt-DR(+)Ft and ppcA-PRFt-DR(–)Ft; Figure 2A) and by analyzing the promoter activities in transgenic tobacco. The GUS activity of the ppcA-PRFt-DR(–)Ft construct in the leaf was comparable to that of the LFt chimerical gene, but the activity of the ppcA-PRFt-DR(+)Ft construct was drastically reduced (Figure 2B). For the ppcA-PRFt-DR(–)Ft construct, histochemical analyses showed that this promoter directed a palisade parenchyma–specific expression of the GUS reporter gene (Figure 2C). It follows from these expression analyses with the C3 plant tobacco that the distal and proximal parts of the promoter will be sufficient for the ppcA1 promoter activity and that the nucleotide sequences between –570 and –1566 are probably not necessary for its expression specificity.
To verify these conclusions, transformation experiments with the C4 plant F. bidentis were performed. F. bidentis is very closely related to F. trinervia and is used for these experiments (Stockhaus et al., 1997
The DR of the C4 ppcA1 Promoter Provides Mesophyll Specificity but No Raised Expression Quantity in the Context of the C3 ppcA1 Promoter The C4-DR could function as a C4 expression module that confers both height and specificity of expression. If this were true, one should expect that upon transfer of the C4-DR into the ppcA1 promoter of the C3 plant F. pringlei, the C4-C3 hybrid promoter would behave like a C4 ppcA1 promoter and show a high level of expression in the mesophyll cells. To test this, the DR of the C3 ppcA1 promoter from nucleotides –2538 to –1854 (Figure 1) was removed, giving rise to ppcA-MFp, and replaced by the C4-DR in correct orientation (Figure 4A).
It is known from previous work (Stockhaus et al., 1997 ) that the ppcA1 promoter of F. pringlei (ppcA-LFp) is relatively weak when compared with the C4 ppcA1 promoter and directs expression in all cells of the leaf, including the vascular bundle. The shortened promoter version ppcA-MFp behaves similarly (Figures 4B and 4C). The addition of the C4-DR to the ppcA-MFp (resulting in ppcA-MFp-DRFt) causes just a small increase in the expression strength (Figure 4B). However, the in situ analysis of the transgenic plants revealed that the C4-C3 chimerical promoter had acquired a mesophyll expression component that was not detectable with the ppcA-MFp construct (Figure 4E). A visual comparison of the in situ promoter activities of ppcA-MFp and ppcA-MFp-DRFt also suggested that the C4-DR did not only add a mesophyll expression component to the ppcA1 promoter part of F. pringle but reduced its original activity in bundle-sheath cells and vascular tissue. We concluded from these experiments that the C4-DR contains mesophyll expression components that are not able to increase the strength of the C3 ppcA1 promoter substantially.
Mapping of cis-Regulatory Elements in the C4 DR of the C4 ppcA1 Promoter
The ppcA-PRFt-DRaFt and ppcA-PRFt-DRbFt promoters directed a clear and reproducible GUS expression in the mesophyll cells (Figures 6C and 6D), although their activities were reduced by  5 to 10 times when compared with the activity of the ppcA-PRFt-DR(+)Ft reference promoter (cf Figures 6B and 3B). This indicates that both the ppcA-PRFt-DRaFt and ppcA-PRFt-DRbFt promoters harbor cis-regulatory elements that are sufficient for mesophyll-specific transcription. By contrast, the ppcA-PRFt-DRcFt promotor produced a minute amount of GUS activity that is below the level of histochemical detection (Figure 6E) but that is higher than the activity of the ppcA-PRFt construct (Figure 6B). This suggested that this segment of the C4-DR might contain some weak transcriptional enhancing element(s). These elements are not essential for mesophyll-specific gene expression, but they may interact with the cis-regulatory elements of the a and b parts, thereby increasing their mesophyll enhancer activity. Subfragments a and b of the C4-DR were able to direct a mesophyll-specific expression. This implies that either the two segments contain distinct and different mesophyll specificity elements or that the overlapping stretch of 41 bp harbors a cis-regulatory element for mesophyll expression. To test these possibilities, one and four tandemly oriented copies of the a/b-overlapping fragment were fused in direct orientation with the PR segment of the C4 ppcA1 promoter. The resulting constructs, ppcA-PRFt-DRa/bFt and ppcA-PRFt-DR4a/bFt (Figure 7A), were analyzed in transgenic F. bidentis.
Both constructs exhibited similar expression levels (Figure 7B) and directed a mesophyll-specific expression of the GUS reporter gene (Figures 7C and 7D). It follows that the a/b overlapping C4-DR fragment contains determinants for mesophyll-specific gene expression, and the segment was designated as Mem1.
The Tetranucleotide CACT Is Essential for Mem1 Function
The comparison of Mem1 and its homolog in F. pringlei shows two remarkable features. The A part differs only in one single nucleotide at the very 5' end (labeled in Figure 8). Mem1 of F. trinervia holds a guanine in this position, and there is an adenine in the Mem1 homolog of F. pringlei. More prominent is the difference in part B. A tetranucleotide (CACT) is present in the Mem1 of F. trinervia but is absent in the F. pringlei sequence. The remainder of part B sequences is virtually identical in both promoters.
To elucidate which of the observed differences between the Mem1 of F. trinervia and its homolog in F. pringlei are candidates for mesophyll expression determinants, we pursued a comparative approach. The 5' flanking sequences of ppcA1-type genes were isolated by vectorette PCR (Siebert et al., 1995 A comparison of the 5' flanking regions identified in each case Mem1 homologous sequences where the A and B parts were, as in F. pringlei, separated by 97 to 108 bp (Figure 8). The A parts of all C4 and C4-like species showed a guanine at their first nucleotide position. An adenine was present in the A homologs of the two C3 species. A more striking C4-to-C3 associated difference is found for the tetranucleotide CACT. This assemblage is present in the B parts of all C4 and C4-like species but lacking in both C3 promoters. This suggested that the CACT tetranucleotide is critical for Mem1 function.
To challenge this assumption, the CACT tetranucleotide was deleted in Mem1 and the modified Mem1, (construct ppcA-PRFt-DRa/bFt-
The C4 cycle genes are largely regulated by transcription (Sheen, 1999 ). This type of gene regulation involves sets of cis-regulatory modules and their corresponding trans-regulatory factors that interact and thereby control the specific expression of the C4 genes in either mesophyll or bundle-sheath cells. Plants with the C4 photosynthetic pathway are of polyphyletic origin (Kellogg, 1999; Sage et al., 1999), and the networks that regulate cell type–specific gene expression are also likely to have evolved several times independently. To date, it is not known which types of cis- and trans-regulatory elements constitute mesophyll or bundle-sheath cell expression modules at the molecular level and how regulatory networks for mesophyll or bundle-sheath cell-specific gene expression have evolved. Here, a scenario is presented that indicates how the mesophyll cell-specific expression of the C4 PEPC gene in the genus Flaveria may have evolved.
Analysis of chimerical promoter/reporter genes in transgenic F. bidentis identified two segments in the 5' flanking region of the ppcA1 gene of the C4 plant F. trinervia that are necessary and sufficient for the mesophyll-specific expression of this gene. The DR exhibits enhancer-like properties and, combined with its corresponding PR, confers high levels of mesophyll expression to the reporter gene (Figure 3). The orthologous ppcA1 promoter of the C3 plant F. pringlei directs neither a high nor a mesophyll-specific expression (Stockhaus et al., 1997 When the DR of the ppcA1 promoter of F. trinervia (C4 ppcA1 promoter) is fused to the ppcA1 promoter of F. pringlei (C3 ppcA1 promoter), a mesophyll expression component is added to that promoter, but the overall promoter strength does not alter substantially (Figure 4). This may be explained by assuming that the DR of the C4 ppcA1 promoter provides mesophyll specificity, while the PR is responsible for quantitative expression. The quantity elements are not present in the C3 ppcA1 promoter, and, therefore, the chimerical ppcA-MFp-DRFt promoter (Figure 4) does not direct high levels of mesophyll expression. Alternatively, the DR of the C4 ppcA1 promoter may contain transcription repressing sequences that reduce ppcA1 expression in the bundle-sheath cells and the vascular bundle and that thereby relatively increase mesophyll expression. However, the activity of all constructs containing the C4 DR or its subfragments is clearly higher than the activity of the PR of the C4 ppcA1 promoter alone (Figures 3, 6, and 7). This demonstrates that the C4 DR contains mesophyll transcriptional enhancer sequences. Whether there are, in addition, bundle-sheath repressing sequences remains an open question.
The proposed attributes of the DRs and PRs of the C4 ppcA1 promoter may not be easily identified by experiments. The PR of the C4 ppcA1 promoter (C4-PR) alone shows only a very basic level of expression (Figure 3). This demonstrates that the DR of the C4 promoter (C4-DR) is absolutely essential for the C4-typical high expression potential of the corresponding PR. On the other hand, the C4-DR does not result in any mesophyll expression when it is fused to the –46 fragment of the 35S promoter of the Cauliflower mosaic virus (Burscheidt, 1998
Are the C4-DR and C4-PR segments the only parts of the 5' flanking region of the C4 ppcA1 gene that are involved in controlling the transcription of that gene? When the ppcA-PRFt-DRFt construct and its derivatives are compared with that of the full C4 ppcA1 promoter (Figures 3 and 6), there is clearly a significant loss in expression quantity. This indicates that the smaller promoter constructs lack quantitative cis-regulatory elements that are present in the full promoter. Alternatively, the reduced expression levels of the ppcA-PRFt-DRFt construct and its derivatives may also be attibutable to the changed distance between the DR and PR segments in these promoters and exhibit topological constraints (Rippe et al., 1995 Whether the C4 ppcA1 promoter sequences between –570 and –1049 encompasses further C4-relevant cis-regulatory elements remains unclear. The C4 ppcA1 promoter deletion experiments with the heterologous C3 plant tobacco suggest that the intermediate region may contain repressing sequences (cf. the expression levels of the ppcA-1,5Ft and ppcA-1,0Ft constructs with the ppcA-PRFt promoter; Figure 2). However, the ppcA-1,5Ft and ppcA-1,0Ft constructs have not been analyzed in the homologous C4 system, and the biological meaning of the tobacco data therefore remains questionable. Even though we cannot exclude that the segment between the DR and PR region contains cis-regulatory elements, we conclude that they are most probably only of minor importance. The DR and PR segments are the major and essential cis-regulatory modules for the high and mesophyll-specific expression of the C4 ppcA1 gene.
To date, the cis-regulatory elements of the PR have not been mapped precisely. Using the yeast one-hybrid system, it was found that the PR of the C4 ppcA1 promoter interacts with homeobox transcription factors of the zinc finger subclass (Windhövel et al., 2001 A cis-regulatory module for mesophyll-specific gene expression named Mem1 has been identified in the DR of the C4 ppcA1 promoter. The module is mapped at 41-bp resolution and overlaps with the a and b parts of the C4-DR segment. Fusing the 41-bp segment to the PR of the C4 ppcA1 promoter is sufficient to confer mesophyll-specific expression to the GUS reporter gene. Mem1, therefore, has to carry cis-regulatory elements for mesophyll-specific gene expression. Whether there are other mesophyll expression elements in the a or b part of the C4-DR segment is unknown. If these elements exist, they are probably redundant to Mem1. Whether Mem1 harbors also a bundle-sheath repressing element remains an open question and should be investigated in the future. A comparative analysis with ppcA1 promoter sequences from other C4, C4-like, and C3 Flaveria species identified Mem1 homologous sequences in all examined plants. Their comparison hinted at elements for mesophyll-specific ppcA1 gene expression. The most notable C4-to-C3 difference detected between Mem1 of the C4/C4-like plants and its counterpart in the C3 species is a CACT tetranucleotide (Figure 8). The motif is present in all Mem1 sequences of the C4/C4-like plants but lacking in the Mem1 homologs of the C3 species. The CACT tetranucleotide is found in a sequence segment, the B region of Mem1, which is fully conserved in the C4 and C3 ppcA1 promoters. This finding suggested that the CACT motif is essential for mesophyll-specific gene expression. Functional analyses with transgenic plants confirmed this assumption. Deletion of the CACT tetranucleotide from Mem1 abolished the mesophyll expression of the GUS reporter gene. We conclude that the addition of the CACT tetranucleotide to the C3 promoter during C3-to-C4 evolution created a new cis-regulatory element that was necessary for confering mesophyll expression to the promoter. Although the deletion of the CACT tetranucleotide reduced promoter activity almost completely, one single transgenic plant out of 10 (i.e., that with the highest activity) expressed the transgene in the mesophyll cells. We do not know whether the expression pattern of this transgene reflects an artifact because of the nearby presence of a mesophyll enhancer within the genome. Therefore, we have to conclude that the CACT-containing cis-regulatory element may not be the only cis-regulatory element in Mem1. The CACT-containing cis-element is necessary but may not be sufficient for mesophyll expression.
The CACT tetranucleotide is embedded in a sequence context (TTACTCACTAA) that can form an imperfect palindrome. The palindrome resembles a binding site for a GCN4-like basic leucine zipper transcription factor (Arndt and Fink, 1986
How did this novel cis-regulatory element evolve? Adjacent to the CACT motif in the 5' direction, two tandem TACT repeats are observed in all C4/C4-like ppcA1 promoters but also in the C3 promoters (Figure 8). Short direct repeats are known to be an important source of genetic change in all organisms because replication misalignment may lead to the deletion or addition of repeat units (Bzymek and Lovett, 2001 A C4-to-C3 associated nucleotide difference was also observed in the A segment of Mem1 (Figure 8). Whereas all C4 and C4-like species have a guanine at the outermost 5' position of Mem1, it is an adenine in the C3 species. No putative transcription factor binding site is detectable in this Mem1 segment; thus, it is not clear whether this nucleotide difference is of functional importance.
The A segment is contiguous with the B segment only in Mem1 of F. trinervia, but in all other C4 and C3 ppcA1 promoters, the two segments are separated from each other by
Which scenario can be envisaged for the evolution of the C4 ppcA promoter in the genus Flaveria? The C3 reference promoter from F. pringlei is weak and does not show any cell specificity. The activity of this promoter is even higher in the bundle-sheath cells and the vascular bundle than in the mesophyll cells. By contrast, the C4 promoter is strong and is active only in the mesophyll cells. Evolution toward C4 could therefore have started by increasing promoter strength. This is supported by ppcA1 mRNA quantification in C3-C4 intermediate Flaveria species. Even C3-C4 intermediates with a low degree of C4 trait expression (i.e., F. chloraefolia; Edwards and Ku, 1987
In his review on biochemical evolution, A.C. Wilson (Wilson et al., 1977
Our investigations on the molecular evolution of C4 PEPC in the genus Flaveria are in line with this concept. The studies show that at the onset of the transition from C3 to C4 photosynthesis, the enzyme is still rather C3-like with respect to its kinetic and regulatory properties; it becomes C4-like only much later (reviewed in Svensson et al., 2003
Construction of Chimerical Promoters DNA manipulations and cloning were performed according to Sambrook and Russell (2001) . All promoter GUS reporter gene fusions used in this work are based on the constructs ppcA-PRFt, ppcA-LFt, and ppcA-LFp, which were formerly designated ppcA-S-Ft, ppcA-L-Ft, and ppcA-L-Fp. Their construction has been described in detail (Stockhaus et al., 1994). In all constructs, the 3' border of the ppcA1 5' flanking sequences of Flaveria trinervia and F. pringlei (Figure 1) is located just upstream of the AUG initiation codon. For cloning purposes, a SmaI site was added to the 3' border of each fragment by PCR amplification with an appropriately designed oligonucleotide. The 5' borders of ppcA-LFt and ppcA-LFp are defined by HindIII (ppcA-LFt) or XbaI sites (ppcA-LFp), which occur naturally in these promoter regions (Figure 1). The 5' border of the ppcA-PRFt promoter fragment of F. trinervia corresponds to nucleotide position –570. A XbaI site was added to this border by PCR amplification. All promoter fragments were assembled in pBluescribe M13– (Stratagene Cloning Systems, La Jolla, CA) and confirmed by sequencing. They were excised by HindIII/SmaI digestion and transferred to HindIII/SmaI-restricted pBI121 (Clontech Laboratories, Palo Alto, CA) in front of the GUS reporter gene (Stockhaus et al., 1994). The ppcA1 promoter reporter gene constructs prepared in the course of this study were cloned as described below. All DNA fragments generated by PCR were confirmed by DNA sequencing.
Construction of ppcA-1,5Ft and ppcA1,0Ft
Construction of ppcA-PRFt-DR(+)Ft and ppcA-PRFt-DR(–)Ft
Construction of ppcA-MFp
Construction of ppcA-MFp-DRFt
Construction of ppcA-PRFt-DRaFt, ppcA-PRFt-DRbFt, and ppcA-PRFt-DRcFt
Construction of ppcA-PRFt-DRa/bFt and ppcA-PRFt-DR4a/bFt The a/b-overlapping region (–1981 to –1940) was amplified by PCR using the FtDEb5' and FtDEa3' primers. After digestion with HindIII and XbaI, the a/b-fragment was inserted into ppcA-PRFt-DR(+)Ft to replace the DR fragment. The resulting promoter was named ppcA-PRFt-DRa/bFt.
Tandem repeats of the a/b-overlapping region were generated as described by de Pater et al. (1993)
Construction of ppcA-PRFt-DRa/bFt-
Plant Transformation
Measurement of GUS Activity and Histochemical Analysis
DNA Isolation
Isolation of 5' Flanking Sequences from the ppcA1 Genes of F. bidentis, F. vaginata, F. palmeri, and F. cronquistii
Sequence data from this article have been deposited with the EMBL/GenBank data libraries under the accession numbers X64143 (F. trinervia), AY297087 (F. bidentis), AY297088 (F. palmeri), AY297090 (F. vaginata), AY297089 (F. cronquistii), and X64144 (F. pringlei).
This work was supported by the Deutsche Forschungsgemeinschaft initially within the Graduiertenkolleg Molekulare Physiologie and later by SFB 590 Inhärente und adaptive Differenzierungsprozesse at the Heinrich Heine University of Düsseldorf. Additional support from the Fonds der Chemischen Industrie is gratefully acknowledged. We are indebted to Uwe Santore for carefully reading the manuscript.
Online version contains Web-only data.  The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Peter Westhoff (west{at}uni-duesseldorf.de). Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.019729. Received December 3, 2003; accepted February 28, 2004.
Arndt, K., and Fink, G.R. (1986). GCN4 protein, a positive transcription factor in yeast, binds general promoters at all 5' TGACTC 3' sequences. Proc. Natl. Acad. Sci. USA 83, 8516–8520. Badger, M. (2003). The roles of carbonic anhydrases in photosynthetic CO2 concentrating mechanisms. Photosyn. Res. 77, 83–94.
Blackwood, E.M., and Kadonaga, J.T. (1998). Going the distance: A current view of enhancer action. Science 281, 60–63.
Bläsing, O.E., Westhoff, P., and Svensson, P. (2000). Evolution of C4 phosphoenolpyruvate carboxylase in Flaveria, a conserved serine residue in the carboxyl-terminal part of the enzyme is a major determinant for C4-specific characteristics. J. Biol. Chem. 275, 27917–27923. Burscheidt, J. (1998). Cis-Regulatorische Determinanten für Mesophyll- und Bündelscheidenspezifische Genexpression in C4-Spezies der Gattung Flaveria—Die Promotoren der Phosphoenolpyruvat-Carboxylase- und der Glycin-Decarboxylasegene. Master's thesis (Düsseldorf, Germany: Heinrich-Heine-Universität).
Bzymek, M., and Lovett, S.T. (2001). Instability of repetitive DNA sequences: The role of replication in multiple mechanisms. Proc. Natl. Acad. Sci. USA 98, 8319–8325. Carroll, S.B. (2000). Endless forms: The evolution of gene regulation and morphological diversity. Cell 101, 577–580.[CrossRef][Web of Science][Medline] Chitty, J.A., Furbank, R.T., Marshall, J.S., Chen, Z., and Taylor, W.C. (1994). Genetic transformation of the C4 plant, Flaveria bidentis. Plant J. 6, 949–956.[CrossRef][Web of Science] Crétin, C., Santi, S., Keryer, E., Lepiniec, L., Tagu, D., Vidal, J., and Gadal, P. (1991). The phosphoenolpyruvate carboxylase gene family of Sorghum: Promoter structures, amino acid sequences and expression of genes. Gene 99, 87–94.[CrossRef][Web of Science][Medline]
de Pater, S., Pham, K., Chua, N.H., Memelink, J., and Kijne, J. (1993). A 22-bp fragment of the pea lectin promoter containing essential TGAC-like motifs confers seed-specific gene expression. Plant Cell 5, 877–886.
Doebley, J., and Lukens, L. (1998). Transcriptional regulators and the evolution of plant form. Plant Cell 10, 1075–1082. Edwards, G.E., and Ku, M.S.B. (1987). Biochemistry of C3-C4 intermediates. In The Biochemistry of Plants, Vol. 10, M.D. Hatch and N.K. Boardman, eds (New York: Academic Press), pp. 275–325. Engelmann, S., Bläsing, O.E., Gowik, U., Svensson, P., and Westhoff, P. (2003). Molecular evolution of C4 phosphoenolpyruvate carboxylase in the genus Flaveria—A gradual increase from C3 to C4 characteristics. Planta 217, 717–725.[CrossRef][Web of Science][Medline] Ernst, K., and Westhoff, P. (1996). The phosphoenolpyruvate carboxylase (ppc) gene family of Flaveria trinervia (C4) and F. pringlei (C3): Molecular characterization and expression analysis of the ppcB and ppcC genes. Plant Mol. Biol. 34, 427–443.[CrossRef] Hatch, M.D. (1987). C4 photosynthesis: A unique blend of modified biochemistry, anatomy and ultrastructure. Biochim. Biophys. Acta 895, 81–106. Hermans, J., and Westhoff, P. (1990). Analysis of expression and evolutionary relationships of phosphoenolpyruvate carboxylase genes in Flaveria trinervia (C4) and F. pringlei (C3). Mol. Gen. Genet. 224, 459–468.[Web of Science][Medline] Hermans, J., and Westhoff, P. (1992). Homologous genes for the C4 isoform of phosphoenolpyruvate carboxylase in a C3- and a C4-Flaveria species. Mol. Gen. Genet. 234, 275–284.[Medline] Höfer, M.U., Santore, U.J., and Westhoff, P. (1992). Differential accumulation of the 10-, 16- and 23-kDa peripheral components of the water-splitting complex of photosystem II in mesophyll and bundle-sheath chloroplasts of the dicotyledonous C4 plant Flaveria trinervia (Spreng.) C. Mohr. Planta 186, 304–312.
Horsch, R.B., Fry, F.E., Hoffmann, N.L., Eichholtz, D., Rogers, S.G., and Fraley, R.T. (1985). A simple and general method for transferring genes into plants. Science 227, 1229–1231. Jefferson, R.A., Kavanagh, T.A., and Bevan, M.W. (1987). GUS fusions: ß-Glucuronidase as a sensitive and versatile gene fusion marker in higher plants. EMBO J. 6, 3901–3907.[Web of Science][Medline] Kellogg, E.A. (1999). Phylogenetic aspects of the evolution of C4 photosynthesis. In C4 Plant Biology, R.F. Sage and R.K. Monson, eds (San Diego, CA: Academic Press), pp. 411–444. Kosugi, S., Ohashi, Y., Nakajima, K., and Arai, Y. (1990). An improved assay for ß-glucuronidase in transformed cells: Methanol almost completely suppresses a putative endogenous ß-glucuronidase activity. Plant Sci. 70, 133–140.[CrossRef] Lazo, G.R., Stein, P.A., and Ludwig, R.A. (1991). A DNA transformation-competent Arabidopsis genomic library in Agrobacterium. Biotechnology 9, 963–967.[CrossRef][Medline]
Li, J.J., and Herskowitz, I. (1993). Isolation of ORC6, a component of the yeast origin recognition complex by a one-hybrid system. Science 262, 1870–1874. Li, Y.-C., Korol, A.B., Fahima, T., Beiles, A., and Nevo, E. (2002). Microsatellites: Genomic distribution, putative functions and mutational mechanisms: A review. Mol. Ecol. 11, 2453–2465.[CrossRef][Medline]
Matys, V., et al. (2003). TRANSFAC: Transcriptional regulation, from patterns to profiles. Nucleic Acids Res. 31, 374–378. Monson, R.K. (1999). The origins of C4 genes and evolutionary pattern in the C4 metabolic phenotype. In C4 Plant Biology, R.F. Sage and R.K. Monson, eds (San Diego, CA: Academic Press), pp. 377–410. Monson, R.K., and Moore, B.D. (1989). On the significance of C3-C4 intermediate photosynthesis to the evolution of C4 photosynthesis. Plant Cell Environ. 12, 689–699.[CrossRef]
Oñate, L., Vicente-Carbajosa, J., Lara, P., Díaz, I., and Carbonero, P. (1999). Barley BLZ2, a seed-specific bZIP protein that interacts with BLZ1 in vivo and activates transcription from the GCN4-like motif of B-hordein promoters in barley endosperm. J. Biol. Chem. 274, 9175–9182. Powell, A.M. (1978). Systematics of Flaveria (Flaveriinae-Asteraceae). Ann. Mo. Bot. Gard. 65, 590–636. Rippe, K., von Hippel, P.H., and Langowski, J. (1995). Action at a distance: DNA-looping and initiation of transcription. Trends Biochem. Sci. 20, 500–506.[CrossRef][Web of Science][Medline] Sage, R.F. (2004). The evolution of C4 photosynthesis. New Phytol. 161, 341–370.[CrossRef] Sage, R.F., Li, M., and Monson, R.K. (1999). The taxonomic distribution of C4 photosynthesis. In C4 Plant Biology, R.F. Sage and R.K. Monson, eds (San Diego, CA: Academic Press), pp. 551–584. Sambrook, J., and Russell, D.W. (2001). Molecular Cloning: A Laboratory Manual. (Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press). Sheen, J. (1999). C4 gene expression. Annu. Rev. Plant Physiol. Plant Mol. Biol. 50, 187–217.[CrossRef][Web of Science]
Siebert, P.D., Chenchik, A., Kellogg, D.E., Lukyanov, K.A., and Lukyanov, S.A. (1995). An improved PCR method for walking in uncloned genomic DNA. Nucleic Acids Res. 23, 1087–1088. Stockhaus, J., Poetsch, W., Steinmüller, K., and Westhoff, P. (1994). Evolution of the C4 phosphoenolpyruvate carboxylase promoter of the C4 dicot Flaveria trinervia: An expression analysis in the C3 plant tobacco. Mol. Gen. Genet. 245, 286–293.[Medline] Stockhaus, J., Schlue, U., Koczor, M., Chitty, J.A., Taylor, W.C., and Westhoff, P. (1997). The promoter of the gene encoding the C4 form of phosphoenolpyruvate carboxylase directs mesophyll specific expression in transgenic C4 Flaveria spp. Plant Cell 9, 479–489.[Abstract] Svensson, P., Bläsing, O., and Westhoff, P. (1997). Evolution of the enzymatic characteristics of C4 phosphoenolpyruvate carboxylase: A comparison of the orthologous ppcA phosphoenolpyruvate carboxylases of Flaveria trinervia (C4) and F. pringlei (C3). Eur. J. Biochem. 246, 452–460.[Web of Science][Medline] Svensson, P., Bläsing, O.E., and Westhoff, P. (2003). Evolution of C4 phosphoenolpyruvate carboxylase. Arch. Biochem. Biophys. 414, 180–188.[CrossRef][Web of Science][Medline] Westhoff, P., and Gowik, U. (2004). Evolution of C4 phosphoenolpyruvate carboxylase. Genes and proteins: A case study with the genus Flaveria. Ann. Bot. 93, 1–11. Westhoff, P., Offermann-Steinhard, K., Höfer, M., Eskins, K., Oswald, A., and Streubel, M. (1991). Differential accumulation of plastid transcripts encoding photosystem II components in the mesophyll and bundle-sheath cells of monocotyledonous NADP-malic enzyme-type C4 plants. Planta 184, 377–388.[Web of Science] Wilson, A.C., Carlson, S.S., and White, T.J. (1977). Biochemical evolution. Annu. Rev. Biochem. 46, 573–639.[CrossRef][Web of Science][Medline] Windhövel, A., Hein, I., Dabrowa, R., and Stockhaus, J. (2001). Characterization of a novel class of plant homeodomain proteins that bind to the C4 phosphoenolpyruvate carboxylase gene of Flaveria trinervia. Plant Mol. Biol. 45, 201–214.[CrossRef][Web of Science][Medline] This article has been cited by other articles:
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ASPB Publications | THE PLANT CELL | PLANT PHYSIOLOGY | |
|---|---|---|---|
TOP
ABSTRACT
INTRODUCTION
CACT; 
