Anaerobically regulated aldolase gene of maize. A chimaeric origin?

Posphoproteomics profiling reveals the regulatory role of a phosphorylated protein PvFBA1 in cadmium tolerance in seashore paspalum

Seashore paspalum (Paspalum vaginatum) is a warm-season and perennial turfgrass and is known for its cadmium (Cd)-stress tolerance. Here, a Phosphoproteomics analysis was performed to examine the key proteins relating to Cd tolerance in seashore paspalum. Fructose 1,6-biphosphate aldolase, PvFBA1, was identified for its phosphorylated state after exposure to Cd stress. Specifically, the phosphorylation of PvFBA1 was enhanced in several metabolic pathways, including pentose phosphate pathway (PPP), carbon fixation and biosynthesis of amino acids under Cd stress. By transforming PvFBA1 into Arabidopsis, the PvFBA1-OE plants exhibited longer roots, greater FBA activity and higher soluble sugar content than WT under 100 µM CdCl2 treatment. By expressing the PvFBA1 in yeast, a serine 50 phosphorylation site was identified as functional site. By microscale thermophoresis experiment, we indicted that PvFBA1can bind Cd directly enhancing its phosphorylation level to alleviate the damage of Cd. This finding may provide new insights into the molecular mechanisms of plants Cd tolerance.

Molecular Characterization, Gene Evolution, and Expression Analysis of the Fructose-1, 6-bisphosphate Aldolase (FBA) Gene Family in Wheat (Triticum aestivum L.)

Fructose-1, 6-bisphosphate aldolase (FBA) is a key plant enzyme that is involved in glycolysis, gluconeogenesis, and the Calvin cycle. It plays significant roles in biotic and abiotic stress responses, as well as in regulating growth and development processes. In the present paper, 21 genes encoding TaFBA isoenzymes were identified, characterized, and categorized into three groups: class I chloroplast/plastid FBA (CpFBA), class I cytosol FBA (cFBA), and class II chloroplast/plastid FBA. By using a prediction online database and genomic PCR analysis of Chinese Spring nulli-tetrasomic lines, we have confirmed the chromosomal location of these genes in 12 chromosomes of four homologous groups. Sequence and genomic structure analysis revealed the high identity of the allelic TaFBA genes and the origin of different TaFBA genes. Numerous putative environment stimulus-responsive cis-elements have been identified in 1,500-bp regions of TaFBA gene promoters, of which the most abundant are the light-regulated elements (LREs). Phylogenetic reconstruction using the deduced protein sequence of 245 FBA genes indicated an independent evolutionary pathway for the class I and class II groups. Although, earlier studies have indicated that class II FBA only occurs in prokaryote and fungi, our results have demonstrated that a few class II CpFBAs exist in wheat and other closely related species. Class I TaFBA was predicted to be tetramers and class II to be dimers. Gene expression analysis based on microarray and transcriptome databases suggested the distinct role of TaFBAs in different tissues and developmental stages. The TaFBA 4-9 genes were highly expressed in leaves and might play important roles in wheat development. The differential expression patterns of the TaFBA genes in light/dark and a few abiotic stress conditions were also analyzed. The results suggested that LRE cis-elements of TaFBA gene promoters were not directly related to light responses. Most TaFBA genes had higher expression levels in the roots than in the shoots when under various stresses. Class I cytosol TaFBA genes, particularly TaFBA10/12/18 and TaFBA13/16, and three class II TaFBA genes are involved in responses to various abiotic stresses. Class I CpFBA genes in wheat are apparently sensitive to different stress conditions.

Two cytosolic aldolases show different expression patterns during shoot elongation in Moso bamboo, Phyllostachys pubescens Mazel

In fast-growing Moso bamboo (Phyllostachys pubescens Mazel), cytosolic fructose 1,6-bisphosphate aldolase (aldolase; EC 4.2.2.13) was more highly active in elongating tissues than in tissues that had already finished elongating. It is well known that the removal of the culm sheath prevents bamboo from elongating. When the sheath was removed from the culm, the aldolase activity was gradually reduced over time. Two isozyme genes for aldolase, PpAldC1 and PpAldC2, were cloned from the elongating tissues of Moso bamboo. Gene expression analysis using a semi-quantitative reverse transcriptase-polymerase chain reaction revealed that PpAldC1 was highly expressed in elongating tissues but was hardly detected in elongated internodes, while PpAldC2 seemed to be expressed constitutively in both elongating and elongated tissues. Promoter analysis revealed that the expression of PpAldC1 was induced by gibberellin. These results indicated that the two genes for cytosolic aldolase in Moso bamboo showed different expression patterns and that one of them was involved in shoot elongation.

Characterization of miRNAs in response to short-term waterlogging in three inbred lines of Zea mays

Waterlogging of plants leads to low oxygen levels (hypoxia) in the roots and causes a metabolic switch from aerobic respiration to anaerobic fermentation that results in rapid changes in gene transcription and protein synthesis. Our research seeks to characterize the microRNA-mediated gene regulatory networks associated with short-term waterlogging. MicroRNAs (miRNAs) are small non-coding RNAs that regulate many genes involved in growth, development and various biotic and abiotic stress responses. To characterize the involvement of miRNAs and their targets in response to short-term hypoxia conditions, a quantitative real time PCR (qRT-PCR) assay was used to quantify the expression of the 24 candidate mature miRNA signatures (22 known and 2 novel mature miRNAs, representing 66 miRNA loci) and their 92 predicted targets in three inbred Zea mays lines (waterlogging tolerant Hz32, mid-tolerant B73, and sensitive Mo17). Based on our studies, miR159, miR164, miR167, miR393, miR408 and miR528, which are mainly involved in root development and stress responses, were found to be key regulators in the post-transcriptional regulatory mechanisms under short-term waterlogging conditions in three inbred lines. Further, computational approaches were used to predict the stress and development related cis-regulatory elements on the promoters of these miRNAs; and a probable miRNA-mediated gene regulatory network in response to short-term waterlogging stress was constructed. The differential expression patterns of miRNAs and their targets in these three inbred lines suggest that the miRNAs are active participants in the signal transduction at the early stage of hypoxia conditions via a gene regulatory network; and crosstalk occurs between different biochemical pathways.

Transcriptional and post-transcriptional regulation of gene expression in submerged root cells of maize

Maize survival under the anaerobic stress due to submergence conditions is dependent on complex metabolic, physiological and morphological adaptation strategies. Here, we focus on gene expression regulation at the transcriptional and post-transcriptional level in submerged maize root cells. Early in progressive oxygen deprivation, root cells sense the low oxygen signal to trigger expressions of TF genes, anaerobic response genes and miRNA genes. The induced TFs, in turn, promote a broad spectrum of responses from morphogenetic to metabolic; these responses occur at later stages of the stress treatment. The selective translation of anaerobically induced transcripts and selective degradation of some APs are also suggested to be an important regulatory mechanism. In addition, miRNAs are possibly transcriptionally regulated in submerged root cells and involved in post-transcriptional control of target genes. Thus, regulation of gene expression in response to low oxygen involves in significant transcriptional and post-transcriptional control.

Pinus taeda phenylpropenal double-bond reductase: purification, cDNA cloning, heterologous expression in Escherichia coli, and subcellular localization in P. taeda

A phenylpropenal double-bond reductase (PPDBR) was obtained from cell suspension cultures of loblolly pine (Pinus taeda L.). Following trypsin digestion and amino acid sequencing, the cDNA encoding this protein was subsequently cloned, with the functional recombinant protein expressed in Escherichia coli and characterized. PPDBR readily converted both dehydrodiconiferyl and coniferyl aldehydes into dihydrodehydrodiconiferyl and dihydroconiferyl aldehydes, when NADPH was added as cofactor. However, it was unable to reduce directly either the double bond of dehydrodiconiferyl or coniferyl alcohols in the presence of NADPH. During this reductive step, the corresponding 4-proR hydrogen was abstracted from [4R-3H]-NADPH during hydride transfer. This is thus the first report of a double-bond reductase involved in phenylpropanoid metabolism, and which is presumed to be involved in plant defense. In situ mRNA hybridization indicated that the PPDBR transcripts in P. taeda stem sections were localized to the vascular cambium, as well as to radial and axial parenchyma cell types. Additionally, using P. taeda cell suspension culture crude protein extracts, dehydrodiconiferyl and coniferyl alcohols could be dehydrogenated to afford dehydrodiconiferyl and coniferyl aldehydes. Furthermore, these same extracts were able to convert dihydrodehydrodiconiferyl and dihydroconiferyl aldehydes into the corresponding alcohols. Taken together, these results indicate that in the crude extracts dehydrodiconiferyl and coniferyl alcohols can be converted to dihydrodehydrodiconiferyl and dihydroconiferyl alcohols through a three-step process, i.e. by initial phenylpropenol oxidation, then sequential PPDBR and phenylpropanal reductions, respectively.

Evolution of the coordinate regulation of glycolytic enzyme genes by hypoxia

Two billion years of aerobic evolution have resulted in mammalian cells and tissues that are extremely oxygen-dependent. Exposure to oxygen tensions outside the relatively narrow physiological range results in cellular stress and toxicity. Consequently, hypoxia features prominently in many human diseases, particularly those associated with blood and vascular disorders, including all forms of anemia and ischemia. Bioenergetic enzymes have evolved both acute and chronic oxygen sensing mechanisms to buffer changes of oxygen tension; at normal P(O) oxidative phosphorylation is the principal energy supply for eukaryotic cells, but when the P(O) falls below a critical mark metabolic switches turn off mitochondrial electron transport and activate anaerobic glycolysis. Without this switch cells would suffer an immediate energy deficit and death at low P(O). An intriguing feature of the switching is that the same conditions that regulate energy metabolism also regulate bioenergetic genes, so that enzyme activity and transcription are regulated simultaneously, albeit with different time courses and signaling pathways. In this review we explore the pathways mediating hypoxia-regulated glycolytic enzyme gene expression, focusing on their atavistic traits and evolution.

Hypoxia regulates beta-enolase and pyruvate kinase-M promoters by modulating Sp1/Sp3 binding to a conserved GC element

The transcription rates of glycolytic enzyme genes are coordinately induced when cells are exposed to low oxygen tension. This effect has been described in many cell types and is not restricted to species or phyla. In mammalian cells, there are 11 distinct glycolytic enzymes, at least 9 of which are induced by hypoxia. Recent reports described a role for the hypoxia-inducible factor-1 (HIF-1) in the transcriptional activation of lactate dehydrogenase A, aldolase-A, phosphoglycerate kinase, and enolase-1 genes. It is not known whether the HIF-1 factor acts exclusively to regulate these genes during hypoxia, or how the other genes of the pathway are regulated. In this paper, we describe analyses of the muscle-specific pyruvate kinase-M and beta-enolase promoters that implicate additional mechanisms for the regulation of glycolytic enzyme gene transcription by hypoxia. Transient transcription of a reporter gene directed by either promoter was activated when transfected muscle cells were exposed to hypoxia. Neither of these promoters contain HIF-1 binding sites. Instead, the hypoxia response was localized to a conserved GC-rich element positioned immediately upstream of a GATAA site in the proximal promoter regions of both genes. The GC element was essential for both basal and hypoxia-induced expression and bound the transcription factors Sp1 and Sp3. Hypoxia caused the progressive depletion of Sp3 determined by DNA binding studies and Western analyses, whereas Sp1 protein levels remained unchanged. Overexpression of Sp3 repressed expression of beta-enolase promoters. It is concluded that hypoxia activates these glycolytic enzyme gene promoters by down-regulating Sp3, thereby removing the associated transcriptional repression.

Evidence for a role for AtMYB2 in the induction of the Arabidopsis alcohol dehydrogenase gene (ADH1) by low oxygen

The transcription factor AtMYB2 binds to two sequence motifs in the promoter of the Arabidopsis ADH1 gene. The binding to the GT-motif (5'-TGGTTT-3') is essential for induction of ADH1 by low oxygen, while binding to the second motif, MBS-2, is not essential for induction. We show that AtMYB2 is induced by hypoxia with kinetics compatible with a role in the regulation of ADH1. Like ADH1, AtMYB2 has root-limited expression. When driven by a constitutive promoter, AtMYB2 is able to transactivate ADH1 expression in transient assays in both Arabidopsis and Nicotiana plumbaginifolia protoplasts, and in particle bombardment of Pisum sativum leaves. Mutation of the GT-motif abolished binding of AtMYB2 and caused loss of activity of the ADH1 promoter in both transient assays and transgenic Arabidopsis plants. These results are consistent with AtMYB2 being a key regulatory factor in the induction of the ADH1 promoter by low oxygen.

Differential regulation of sugar-sensitive sucrose synthases by hypoxia and anoxia indicate complementary transcriptional and posttranscriptional responses

The goal of this research was to resolve the hypoxic and anoxic responses of maize (Zea mays) sucrose (Suc) synthases known to differ in their sugar regulation. The two maize Suc synthase genes, Sus1 and Sh1, both respond to sugar and O2, and recent work suggests commonalities between these signaling systems. Maize seedlings (NK508 hybrid, W22 inbred, and an isogenic sh1-null mutant) were exposed to anoxic, hypoxic, and aerobic conditions (0, 3, and 21% O2, respectively), when primary roots had reached approximately 5 cm. One-centimeter tips were excised for analysis during the 48-h treatments. At the mRNA level, Sus1 was rapidly up-regulated by hypoxia (approximately 5-fold in 6 h), whereas anoxia had less effect. In contrast, Sh1 mRNA abundance increased strongly under anoxia (approximately 5-fold in 24 h) and was much less affected by hypoxia. At the enzyme level, total Suc synthase activity rose rapidly under hypoxia but showed little significant change during anoxia. The contributions of SUS1 and SH1 activities to these responses were dissected over time by comparing the sh1-null mutant with the isogenic wild type (Sus+, Sh1+). Sh1-dependent activity contributed most markedly to a rapid protein-level response consistently observed in the first 3 h, and, subsequently, to a long-term change mediated at the level of mRNA accumulation at 48 h. A complementary midterm rise in SUS1 activity varied in duration with genetic background. These data highlight the involvement of distinctly different genes and probable signal mechanisms under hypoxia and anoxia, and together with earlier work, show parallel induction of "feast and famine" Suc synthase genes by hypoxia and anoxia, respectively. In addition, complementary modes of transcriptional and posttranscriptional regulation are implicated by these data, and provide a mechanism for sequential contributions from the Sus1 and Sh1 genes during progressive onset of naturally occurring low-O2 events.

OXYGEN DEFICIENCY AND ROOT METABOLISM: Injury and Acclimation Under Hypoxia and Anoxia

Oxygen deficiency in the rooting zone occurs with poor drainage after rain or irrigation, causing depressed growth and yield of dryland species, in contrast with native wetland vegetation that tolerates such conditions. This review examines how roots are injured by O2 deficiency and how metabolism changes during acclimation to low concentrations of O2. In the root apical meristem, cell survival is important for the future development; metabolic changes under anoxia help maintain cell survival by generating ATP anaerobically and minimizing the cytoplasmic acidosis associated with cell death. Behind the apex, where cells are fully expanded, ethylene-dependent death and lysis occurs under hypoxia to form continuous, gas-filled channels (aerenchyma) conveying O2 from the leaves. This selective sacrifice of cells may resemble programmed cell death and is distinct from cell death caused by anoxia. Evidence concerning alternative possible mechanisms of anoxia tolerance and avoidance is presented.

Accumulation of cytosolic glyceraldehyde-3-phosphate dehydrogenase RNA under biological stress conditions and elicitor treatments in potato

Plants respond to pathogen infection and environmental stress by regulating the coordinate expression of many stress-related genes. In plants, the expression of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is induced under environmental stress. This work was aimed at investigating whither the expression pattern of cytosolic GAPDH is also modulated upon infection of potato plants (Solanum tuberosum L.) with the late blight fungal agent Phytophthora infestans. Northern blot analysis showed the accumulation of the GAPDH gene transcripts in leaves and stems of inoculated potato plants. When tuber discs were treated with eicosapentaenoic acid (EPA), an elicitor found in P. infestans, GAPDH gene transcripts level increased. The increase was parallel to that of the hydroxymethyl glutharyl coenzyme A reductase (HMGR), an enzyme involved in pathogen defense reactions. Glucans obtained from P. infestans cell wall acts synergistically with EPA on GAPDH and HMGR gene induction. Salicylic acid, an endogenous signal for inducing systemic acquired resistance, was also effective in stimulating the GAPDH transcript accumulation in potato leaves. These experiments suggest that related multi-component factors, which are part of both primary and secondary metabolism, are probably regulated by similar signal transduction pathways when they are induced under biotic or abiotic stress conditions.

Isolation and characterization of the Adh2 5' region from Petunia hybrida

The Adh2 gene from Petunia hybrida has been difficult to clone; exons 1 to 8 were isolated using PCR after unsuccessful screening of three genomic libraries. A combination of inverse and direct PCR strategies has been used to isolate upstream regions of Adh2. Here we report the cloning strategy for the nucleotide sequence of the 5' region of Adh2 from P. hybrida, the locations of the transcriptional start site and putative TATA box, as well as comparative analyses of the upstream regions of petunia Adh2, other Adh genes and other genes induced by hypoxia.

Genomic structure of the rice aldolase isozyme C-1 gene and its regulation through a Ca 2+ -mediated protein kinase-phosphatase pathway

Complementary and genomic DNA clones coding for aldolase C-1, the fourth-type isozyme of aldolase in rice Oryza sativa L., have been characterized. The organization of the gene is quite similar to those encoding rice aldolase C-a and a maize cytoplasmic-type aldolase, in that introns are located in the same position. Amino acid sequences are highly conserved among cytoplasmic aldolases in plants. Expression of the gene in rice callus is activated by a protein phosphatase inhibitor okadaic acid, and is inhibited in the presence of thapsigargin, a reagent which increases calcium influx into the cytoplasm. The inhibition is rescued by the simultaneous addition of protein kinase inhibitor H-7. Thus, it is suggested that expression of the aldolase C-1 gene is regulated through a signal transduction pathway involving a Ca 2+ -mediated protein kinase-protein phosphatase system.

The plastid aldolase gene from Chlamydomonas reinhardtii: intron/exon organization, evolution, and promoter structure

Genomic clones encoding the plastidic fructose-1,6-bisphosphate aldolase of Chlamydomonas reinhardtii were isolated and sequenced. The gene contains three introns which are located within the coding sequence for the mature protein. No introns are located within or near the sequence encoding the transit-peptide, in contrast to the genes for plastidic aldolases of higher plants. Neither the number nor the positions of the three introns of the C. reinhardtii aldolase gene are conserved in the plastidic or cytosolic aldolase genes of higher plants and animals. The 5' border sequences of introns in the aldolase gene of C. reinhardtii exhibit the conserved plant consensus sequence. The 3' acceptor splice sites for introns 1 and 3 show much less similarity to the eukaryotic consensus sequences than do those of intron 2. The plastidic aldolase gene has two tandemly repeated CAAT box motifs in the promoter region. Genomic Southern blots indicate that the gene is encoded by a single locus in the C. reinhardtii genome.

Structure of the tomato Adh2 gene and Adh2 pseudogenes, and a study of Adh2 gene expression in fruit

A cDNA library was constructed from RNA from the pericarp of ripe tomato fruit and four cDNAs encoding ADH2 were isolated and characterized. The cDNAs encode a peptide 379 amino acids in length. They hybridized strongly with a 1.8 kb RNA species well represented in RNA from ripe, but not from mature, unripe fruit, and strongly to a similar RNA species present in hypoxic, but not in aerobic roots. Northern analysis showed that the mRNA for ADH2 in fruit increased in abundance through ripening, particularly during late ripening. In pericarp tissue of fruit, the Adh2 mRNA level increased to a maximum within 8-16 h of exposure to atmospheres with 3% (v/v) oxygen, and returned to the basal level within 16 h of a return to air. The mRNA level was sensitive to the oxygen level in the atmosphere, increasing 20-fold in 12% (v/v) oxygen and 100-fold in 3% oxygen. The homologous tomato Adh2 gene was isolated from a genomic library. The gene has an overall length of 2334 bp from transcription start site to poly(A) addition site and includes eight introns. Southern blot analysis of tomato genomic DNA identified multiple Adh2-related sequences. Two of these, PSA1 and PSA2, were cloned and found to have 94% similarity with each other and 77% similarity with the tomato Adh2 gene over a 1000 bp region. The homologous regions include introns and exons but the equivalent exons contain frame shifts, deletions and stop codons. The two regions are therefore presumptive pseudogenes.

Structural analysis of the chloroplastic and cytoplasmic aldolase-encoding genes implicated the occurrence of multiple loci in rice

The genes AldP and AldC-a, encoding the rice chloroplastic (cp) and cytoplasmic (ct) types of aldolase, respectively, were isolated and sequenced, and their transcription start points (tsp) were determined. Organization of the two genes was found to differ greatly; AldP consisted of six exons while AldC-a consisted of two exons. The deduced amino acid (aa) sequence of AldP contained a cp stromal targeting signal, followed by a sequence that matches the experimentally determined N-terminal sequence of mature AldP. The two enzymes share only 55% aa identity. However, rice AldP had about 73% homology with the cp aldolase of spinach. Also, the homology of AldC-a with maize, spinach and Arabidopsis thaliana cytoplasmic aldolases ranged from 70 to 90%. Southern blot analyses indicated that AldP is encoded at a single locus, whereas the gene encoding the ct counterpart is distributed at three loci on the genome. This feature is quite different from those of maize and spinach, in which only one locus was found for the ct aldolase.

Hypoxically inducible barley alanine aminotransferase: cDNA cloning and expression analysis

A 1.75 kb cDNA containing the entire coding sequence of the hypoxically inducible alanine aminotransferase (AlaAT) from barley roots was isolated and sequenced. This clone has an open reading frame of 1446 bp, and a deduced amino acid sequence of 482 residues, giving an estimated protein molecular mass of 52,885 Da. RNA blot analysis of barley root tissue showed a 4-fold increase of a single AlaAT-2 mRNA band after 12-24 hours of hypoxic stress, followed by a decrease in message levels after 48 h of hypoxic conditions. AlaAT-2 protein concentration increased in a similar pattern to AlaAT activity in root tissue, to almost 6-fold the aerobic level after 96 h of hypoxic stress. AlaAT-2 activity increased more than 2-fold in roots of Panicum miliaceum exposed to hypoxia, and is the same isoform as the light inducible AlaAT in P. miliaceum leaves. The unique expression patterns of AlaAT-2 in root and leaf tissue upon exposure to different environmental stimuli is also discussed.

Anaerobiosis and plant growth hormones induce two genes encoding 1-aminocyclopropane-1-carboxylate synthase in rice (Oryza sativa L.)

The plant hormone ethylene is believed to be responsible for the ability of rice to grow in the deepwater regions of Southeast Asia. Ethylene production is induced by hypoxia, which is caused by flooding, because of enhanced activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, the key enzyme in the ethylene biosynthetic pathway. We have cloned three divergent members, (OS-ACS1, OS-ACS2, and OS-ACS3), of a multigene family encoding ACC synthase in rice. OS-ACS1 resides on chromosome 3 and OS-ACS3 on chromosome 5 in the rice genome. The OS-ACS1 and OS-ACS3 genes are induced by anaerobiosis and indoleacetic acid (IAA) + benzyladenine (BA) + LiCl treatment. The anaerobic induction is differential and tissue specific; OS-ACS1 is induced in the shoots, whereas OS-ACS3 is induced in the roots. These inductions are insensitive to protein synthesis inhibitors, suggesting that they are primary responses to the inducers. All three genes are actually induced when protein synthesis is inhibited, indicating that they may be under negative control or that their mRNAs are unstable. The OS-ACS1 gene was structurally characterized, and the function of its encoded protein (M(r) = 53 112 Da, pI 8.2) was confirmed by expression experiments in Escherichia coli. The protein contains all eleven invariant amino acid residues that are conserved between aminotransferases and ACC synthases cloned from various dicotyledonous plants. The amino acid sequence shares significant identity to other ACC synthases (69-34%) and is more similar to sequences in other plant species (69% with the tomato LE-ACS3) than to other rice ACC synthases (50-44%). The data suggest that the extraordinary degree of divergence among ACC synthase isoenzymes within each species arose early in plant evolution and before the divergence of monocotyledonous and dicotyledonous plants.

Plant aldolase: cDNA and deduced amino-acid sequences of the chloroplast and cytosol enzyme from spinach

We report the sequences of full-length cDNAs for the nuclear genes encoding the chloroplastic and cytosolic fructose-1,6-bisphosphate aldolase (EC 4.1.2.13) from spinach. A comparison of the deduced amino-acid sequences with one another and with published cytosolic aldolase sequences of other plants revealed that the two enzymes from spinach share only 54% homology on their amino acid level whereas the homology of the cytosolic enzyme of spinach with the known sequences of cytosolic aldolases of maize, rice and Arabidopsis range from 67 to 92%. The sequence of the chloroplastic enzyme includes a stroma-targeting N-terminal transit peptide of 46 amino acid residues for import into the chloroplast. The transit peptide exhibits essential features similar to other chloroplast transit peptides. Southern blot analysis implies that both spinach enzymes are encoded by single genes.

Functional properties of the anaerobic responsive element of the maize Adh1 gene

The functional properties of the anaerobic responsive element (ARE) of the maize Adh1 gene have been analysed using a transient expression assay in electroporated maize protoplasts. The ARE functions in both orientations although inversion of the ARE sequence relative to the TATA box element produces slightly weaker promoter activity under anaerobic conditions and elevated expression under aerobic conditions. Promoter activity under anaerobic conditions is proportional to the number of complete ARE sequences in the Adh1 promoter. The ARE contains two sub-regions and dimers of sub-region II are as efficient as the wild-type sequence in activating gene expression under anaerobic conditions. However, sub-region I dimers do not appear capable of inducing gene expression in response to anaerobic stress. We conclude that sub-region II is essential for anaerobic induction of gene expression. Reporter gene expression remains constant when the spacing between sub-regions of the ARE is increased up to at least 64 bp, but increased spacing of 136 bp or greater abolishes expression in both aerobic and anaerobic conditions, indicating that a close association of the two sub-regions is required both for anaerobic responsiveness and for maximal levels of aerobic gene expression. When the ARE is placed upstream of position -90 of the CaMV 35S promoter, the ARE produces a high level of expression in both aerobic and anaerobic conditions. The general enhancement of gene expression driven by the hybrid ARE/35S promoter in aerobic conditions requires an intact sub-region II motif since mutation or deletion of sub-region II from the hybrid promoter reduces the level of expression to that observed for the truncated 35S promoter alone. In addition, mutation of the sub-region I sequences in the ARE/35S hybrid promoter does not significantly reduce expression in aerobic conditions, relative to pARE/delta 35S(-90), suggesting that sub-region I does not contribute to this general enhancer function.

Alcohol dehydrogenase III in Aspergillus nidulans is anaerobically induced and post-transcriptionally regulated

An alcohol dehydrogenase was shown to be induced in Aspergillus nidulans by periods of anaerobic stress. This alcohol dehydrogenase was shown to correspond to the previously described cryptic enzyme, alcohol dehydrogenase III (McKnight et al. 1985), by analysis of a mutation in the structural gene of alcohol dehydrogenase III, alcC, created by gene disruption. Survival tests on agar plates showed that this enzyme is required for long-term survival under anaerobic conditions. Northern blot analysis and gene fusion studies showed that the expression of the alcC gene is regulated at both the transcriptional and translational levels. Thus there are mechanisms in this filamentous fungus allowing survival under anaerobic stress that are similar to those described in higher plants.

Molecular analysis of an alcohol dehydrogenase-encoding genomic clone (adh2) from rice

An alcohol dehydrogenase-encoding gene was isolated from a rice genomic library. The coding region was sequenced, and the gene was identified as adh2. The nucleotide sequence of this gene contains an open reading frame which is interrupted by nine introns. Sequences that are important for eukaryotic gene expression, e.g. the TATA box, polyadenylation signal, intron/exon junction and putative splicing branch sites, are found in the expected locations in the rice adh2. A sequence related to the hexanucleotide core of regulatory elements identified in anaerobically induced plant genes is also present in the 5' region of the rice adh2.