A cis-acting element and a trans-acting factor involved in the wound-induced expression of a horseradish peroxidase gene

Transcriptome Analysis and Functional Validation Identify a Putative bZIP Transcription Factor, Fpkapc, that Regulates Development, Stress Responses, and Virulence in Fusarium pseudograminearum

Fusarium pseudograminearum is a soilborne, hemibiotrophic phytopathogenic fungus that causes Fusarium crown rot and Fusarium head blight in wheat. The basic leucine zipper proteins (bZIPs) are evolutionarily conserved transcription factors that play crucial roles in a range of growth and developmental processes and the responses to biotic and abiotic stresses. However, the roles of bZIP transcription factors remains unknown in F. pseudograminearum. In this study, a bZIP transcription factor Fpkapc was identified to localize to the nucleus in F. pseudograminearum. A mutant strain (Δfpkapc) was constructed to determine the role of Fpkapc in growth and pathogenicity of F. pseudograminearum. Transcriptomic analyses revealed that many genes involved in basic metabolism and oxidation-reduction processes were downregulated, whereas many genes involved in metal iron binding were upregulated in the Δfpkapc strain, compared with the wild type (WT). Correspondingly, the mutant had severe growth defects and displayed abnormal hyphal tips. Conidiation in the Fpkapc mutant was reduced, with more conidia in smaller size and fewer septa than in the WT. Also, relative to WT, the Δfpkapc strain showed greater tolerance to ion stress, but decreased tolerance to H₂O₂. The mutant caused smaller disease lesions on wheat and barley plants, but significantly increased TRI gene expression, compared with the WT. In summary, Fpkapc plays multiple roles in governing growth, development, stress responses, and virulence in F. pseudograminearum.

GmWRKY40, a member of the WRKY transcription factor genes identified from Glycine max L., enhanced the resistance to Phytophthora sojae

BACKGROUND

The WRKY proteins are a superfamily of transcription factors and members play essential roles in the modulation of diverse physiological processes, such as growth, development, senescence and response to biotic and abiotic stresses. However, the biological roles of the majority of the WRKY family members remains poorly understood in soybean relative to the research progress in model plants.

RESULTS

In this study, we identified and characterized GmWRKY40, which is a group IIc WRKY gene. Transient expression analysis revealed that the GmWRKY40 protein is located in the nucleus of plant cells. Expression of GmWRKY40 was strongly induced in soybean following infection with Phytophthora sojae, or treatment with methyl jasmonate, ethylene, salicylic acid, and abscisic acid. Furthermore, soybean hairy roots silencing GmWRKY40 enhanced susceptibility to P. sojae infection compared with empty vector transgenic roots. Moreover, suppression of GmWRKY40 decreased the accumulation of reactive oxygen species (ROS) and modified the expression of several oxidation-related genes. Yeast two-hybrid experiment combined with RNA-seq analysis showed that GmWRKY40 interacted with 8 JAZ proteins with or without the WRKY domain or zinc-finger domain of GmWRKY40, suggesting there were different interaction patterns among these interacted proteins.

CONCLUSIONS

Collectively, these results suggests that GmWRKY40 functions as a positive regulator in soybean plants response to P. sojae through modulating hydrogen peroxide accumulation and JA signaling pathway.

NF-YB1-YC12-bHLH144 complex directly activates Wx to regulate grain quality in rice (Oryza sativa L.)

Identification of seed development regulatory genes is the key for the genetic improvement in rice grain quality. NF-Ys are the important transcription factors, but their roles in rice grain quality control and the underlying molecular mechanism remain largely unknown. Here, we report the functional characterization a rice NF-Y heterotrimer complex NF-YB1-YC12-bHLH144, which is formed by the binding of NF-YB1 to NF-YC12 and then bHLH144 in a sequential order. Knock-out of each of the complex genes resulted in alteration of grain qualities in all the mutants as well as reduced grain size in crnf-yb1 and crnf-yc12. RNA-seq analysis identified 1496 genes that were commonly regulated by NF-YB1 and NF-YC12, including the key granule-bound starch synthase gene Wx. NF-YC12 and bHLH144 maintain NF-YB1 stability from the degradation mediated by ubiquitin/26S proteasome, while NF-YB1 directly binds to the 'G-box' domain of Wx promoter and activates Wx transcription, hence to regulate rice grain quality. Finally, we revealed a novel grain quality regulatory pathway controlled by NF-YB1-YC12-bHLH144 complex, which has great potential for rice genetic improvement.

Transient Expression and Purification of Horseradish Peroxidase C in Nicotiana benthamiana

Horseradish peroxidase (HRP) is a commercially important reagent enzyme used in molecular biology and in the diagnostic product industry. It is typically purified from the roots of the horseradish (Armoracia rusticana); however, this crop is only available seasonally, yields are variable and often low, and the product is a mixture of isoenzymes. Engineering high-level expression in transiently transformed tobacco may offer a solution to these problems. In this study, a synthetic Nicotiana benthamiana codon-adapted full-length HRP isoenzyme gene as well as C-terminally truncated and both N- and C-terminally truncated versions of the HRP C gene were synthesized, and their expression in N. benthamiana was evaluated using an Agrobacterium tumefaciens-mediated transient expression system. The influence on HRP C expression levels of co-infiltration with a silencing suppressor (NSs) construct was also evaluated. Highest HRP C levels were consistently obtained using either the full length or C-terminally truncated HRP C constructs. HRP C purification by ion exchange chromatography gave an overall yield of 54% with a Reinheitszahl value of >3 and a specific activity of 458 U/mg. The high level of HRP C production in N. benthamiana in just five days offers an alternative, viable, and scalable system for production of this commercially significant enzyme.

Stress-Mediated cis-Element Transcription Factor Interactions Interconnecting Primary and Specialized Metabolism in planta

Plant specialized metabolites are being used worldwide as therapeutic agents against several diseases. Since the precursors for specialized metabolites come through primary metabolism, extensive investigations have been carried out to understand the detailed connection between primary and specialized metabolism at various levels. Stress regulates the expression of primary and specialized metabolism genes at the transcriptional level via transcription factors binding to specific cis-elements. The presence of varied cis-element signatures upstream to different stress-responsive genes and their transcription factor binding patterns provide a prospective molecular link among diverse metabolic pathways. The pattern of occurrence of these cis-elements (overrepresentation/common) decipher the mechanism of stress-responsive upregulation of downstream genes, simultaneously forming a molecular bridge between primary and specialized metabolisms. Though many studies have been conducted on the transcriptional regulation of stress-mediated primary or specialized metabolism genes, but not much data is available with regard to cis-element signatures and transcription factors that simultaneously modulate both pathway genes. Hence, our major focus would be to present a comprehensive analysis of the stress-mediated interconnection between primary and specialized metabolism genes via the interaction between different transcription factors and their corresponding cis-elements. In future, this study could be further utilized for the overexpression of the specific transcription factors that upregulate both primary and specialized metabolism, thereby simultaneously improving the yield and therapeutic content of plants.

Sweet potato NAC transcription factor, IbNAC1, upregulates sporamin gene expression by binding the SWRE motif against mechanical wounding and herbivore attack

Sporamin is a tuberous storage protein with trypsin inhibitory activity in sweet potato (Ipomoea batatas Lam.), which accounts for 85% of the soluble protein in tubers. It is constitutively expressed in tuberous roots but is expressed in leaves only after wounding. Thus far, its wound-inducible signal transduction mechanisms remain unclear. In the present work, a 53-bp DNA region, sporamin wound-response cis-element (SWRE), was identified in the sporamin promoter and was determined to be responsible for the wounding response. Using yeast one-hybrid screening, a NAC domain protein, IbNAC1, that specifically bound to the 5'-TACAATATC-3' sequence in SWRE was isolated from a cDNA library from wounded leaves. IbNAC1 was constitutively expressed in root tissues and was induced earlier than sporamin following the wounding of leaves. Transgenic sweet potato plants overexpressing IbNAC1 had greatly increased sporamin expression, increased trypsin inhibitory activity, and elevated resistance against Spodoptera litura. We further demonstrated that IbNAC1 has multiple biological functions in the jasmonic acid (JA) response, including the inhibition of root formation, accumulation of anthocyanin, regulation of aging processes, reduction of abiotic tolerance, and overproduction of reactive oxygen species (ROS). Thus, IbNAC1 is a core transcription factor that reprograms the transcriptional response to wounding via the JA-mediated pathway in sweet potato.

Roles of apoplastic peroxidases in plant response to wounding

Apoplastic class III peroxidases (EC 1.11.1.7) play key roles in the response of plants to pathogen infection and abiotic stresses, including wounding. Wounding is a common stress for plants that can be caused by insect or animal grazing or trampling, or result from agricultural practices. Typically, mechanical damage to a plant immediately induces a rapid release and activation of apoplastic peroxidases, and an oxidative burst of reactive oxygen species (ROS), followed by the upregulation of peroxidase genes. We discuss how plants control the expression of peroxidases genes upon wounding, and also the sparse information on peroxidase-mediated signal transduction pathways. Evidence reviewed here suggests that in many plants production of the ROS that comprise the initial oxidative burst results from a complex interplay of peroxidases with other apoplastic enzymes. Later responses following wounding include various forms of tissue healing, for example through peroxidase-dependent suberinization, or cell death. Limited data suggest that ROS-mediated death signalling during the wound response may involve the peroxidase network, together with other redox molecules. In conclusion, the ability of peroxidases to both generate and scavenge ROS plays a key role in the involvement of these enigmatic enzymes in plant stress tolerance.

Identification of transcriptional regulatory nodes in soybean defense networks using transient co-transactivation assays

Plant responses to major environmental stressors, such as insect feeding, not only occur via the functions of defense genes but also involve a series of regulatory factors. Our previous transcriptome studies proposed that, in addition to two defense-related genes, GmVSPβ and GmN:IFR, a high proportion of transcription factors (TFs) participate in the incompatible soybean-common cutworm interaction networks. However, the regulatory mechanisms and effects of these TFs on those induced defense-related genes remain unknown. In the present work, we isolated and identified 12 genes encoding MYB, WRKY, NAC, bZIP, and DREB TFs from a common cutworm-induced cDNA library of a resistant soybean line. Sequence analysis of the promoters of three co-expressed genes, including GmVSPα, GmVSPβ, and GmN:IFR, revealed the enrichment of various TF-binding sites for defense and stress responses. To further identify the regulatory nodes composed of these TFs and defense gene promoters, we performed extensive transient co-transactivation assays to directly test the transcriptional activity of the 12 TFs binding at different levels to the three co-expressed gene promoters. The results showed that all 12 TFs were able to transactivate the GmVSPβ and GmN:IFR promoters. GmbZIP110 and GmMYB75 functioned as distinct regulators of GmVSPα/β and GmN:IFR expression, respectively, while GmWRKY39 acted as a common central regulator of GmVSPα/β and GmN:IFR expression. These corresponding TFs play crucial roles in coordinated plant defense regulation, which provides valuable information for understanding the molecular mechanisms involved in insect-induced transcriptional regulation in soybean. More importantly, the identified TFs and suitable promoters can be used to engineer insect-resistant plants in molecular breeding studies.

Molecular analysis and expression of a floral organ-specific polygalacturonase gene isolated from rapeseed (Brassica napus L.)

High throughput screening of stage-specific differentially expressed genes in a Brassica napus two-line Rs1046A/B subtractive library was used to identify the BnQRT3 gene associated with cell wall metabolism. Phylogenetic analysis indicates the protein product of BnQRT3 is polygalacturonase. According to cytological comparisons of Rs1046 sterile and fertile anthers, RT-PCR studies and in situ hybridizations, BnQRT3 is expressed most strongly in floral organs and may play an essential role in pollen maturation. Analysis of the histological staining pattern of BnQRT3 promoter-GUS constructs in transgenic Arabidopsis and Brassica napus revealed that proximal part of 5'-flanking region directed expression in the vascular tissue of filaments, veins in sepal and petals, stigma, branch connective and the floral organ abscission zone during the open flower stage. In the meanwhile, Activity of BnQRT3 was detected in the anthers, which commences at the microsporocyte stage and persists as anther approaches dehiscence. Strong GUS expression also can be observed in the vascular tissue of leaves and stem by compression with forceps or excision, suggesting that the BnQRT3 promoter is responsive to wounding.

Analysis of class III peroxidase genes expressed in roots of resistant and susceptible wheat lines infected by Heterodera avenae

The response of resistant wheat-Aegilops ventricosa introgression line H-93-8 and its susceptible parent, Triticum aestivum H-10-15, to Ha71 Spanish population of Heterodera avenae was studied to determine the changes in peroxidase gene expression during incompatible and compatible wheat-nematode interactions. Twenty peroxidase genes were characterized from both 211 expressed sequence tags and 259 genomic DNA clones. Alignment of deduced amino acid sequences and phylogenetic clustering with peroxidases from other plant species showed that these enzymes fall into seven different groups (designated TaPrx108 to TaPrx114) which represent peroxidases secreted to the apoplast by a putative N-terminal peptide signal. TaPrx111, TaPrx112, and TaPrx113 were induced by nematode infection in both genotypes but with differing magnitude and timing. TaPrx112 and TaPrx113 groups increased more in resistant than in susceptible infected lines. In addition, in situ hybridization analyses of genes belonging to TaPrx111, TaPrx112, and TaPrx113 groups revealed a more intense signal in cells close to the vascular cylinder and parenchyma vascular cells of resistant than susceptible wheat when challenged by nematodes. These data seem to suggest that wheat apoplastic peroxidases, because of their different expression in quantity and timing, play different roles in the plant response to nematode infection.

A novel wound-responsive cis-element, VWRE, of the vascular system-specific expression of a tobacco peroxidase gene, tpoxN1

The wound-induced expression of tpoxN1, encoding a tobacco peroxidase, is unique because of its vascular system-specific expression and insensitivity to known wound-signal compounds such as jasmonic acid, ethylene, and plant hormones [Sasaki et al. (2002) Plant Cell Physiol 43:108-117]. To study the mechanism of expression, the 2-kbp tpoxN1 promoter region and successive 5'-deletion of the promoter were introduced as GUS fusion genes into tobacco plants. Analysis of GUS activity in transgenic plants indicated that a vascular system-specific and wound-responsive cis-element (VWRE) is present at the -239/-200 region of the promoter. Gel mobility shift assays suggested that a nuclear factor(s) prepared from wounded tobacco stems binds a 14-bp sequence (-229/-215) in the -239/-200 region in a sequence-specific manner. A mutation in this 14-bp region of the -239 promoter fragment resulted in a considerable decrease in wound-responsive GUS activity in transgenic plants. An 11-bp sequence, which completely overlaps with the 14-bp sequence, was found in the 5' distal region (-420/-410) and is thought to contribute to the wound-induced expression together with the 14-bp. The -114-bp core promoter of the tpoxN1 gene was indispensable for wound-induced expression, indicating that the 14-bp region is a novel wound-responsive cis-element VWRE, which may work cooperatively with other factors in the promoter.

An egg apparatus-specific enhancer of Arabidopsis, identified by enhancer detection

Despite a central role in angiosperm reproduction, few gametophyte-specific genes and promoters have been isolated, particularly for the inaccessible female gametophyte (embryo sac). Using the Ds-based enhancer-detector line ET253, we have cloned an egg apparatus-specific enhancer (EASE) from Arabidopsis (Arabidopsis thaliana). The genomic region flanking the Ds insertion site was further analyzed by examining its capability to control gusA and GFP reporter gene expression in the embryo sac in a transgenic context. Through analysis of a 5' and 3' deletion series in transgenic Arabidopsis, the sequence responsible for egg apparatus-specific expression was delineated to 77 bp. Our data showed that this enhancer is unique in the Arabidopsis genome, is conserved among different accessions, and shows an unusual pattern of sequence variation. This EASE works independently of position and orientation in Arabidopsis but is probably not associated with any nearby gene, suggesting either that it acts over a large distance or that a cryptic element was detected. Embryo-specific ablation in Arabidopsis was achieved by transactivation of a diphtheria toxin gene under the control of the EASE. The potential application of the EASE element and similar control elements as part of an open-source biotechnology toolkit for apomixis is discussed.

Molecular cloning of a pathogen/wound-inducible PR10 promoter from Pinus monticola and characterization in transgenic Arabidopsis plants

In Pinus monticola (Dougl. ex D. Don), the class ten pathogenesis-related (PR10) proteins comprise a family of multiple members differentially expressed upon pathogen infection and other environmental stresses. One of them, PmPR10-1.13, is studied here by investigating its transcriptional regulation in transgenic Arabidopsis plants. For functional analyses of the PmPR10-1.13 promoter, a 1,316-bp promoter fragment and three 5' deletions were translationally fused to the ss-glucuronidase (GUS) reporter gene. The 1,316-bp promoter-driven GUS activity first appeared in hypocotyls and cotyledons in 2- to 3-day-old seedlings. As transgenic plants grew, GUS activity was detected strongly in apical meristems, next in stems and leaves. No GUS activity was detected in roots and in reproductive tissues of flower organs. In adult plants, the PmPR10-1.13 promoter-directed GUS expression was upregulated following pathogen infection and by wounding treatment, which generally mimic the endogenous expression pattern in western white pine. Promoter analysis of 5' deletions demonstrated that two regions between -1,316 and -930, and between -309 and -100 were responsible for the wound responsiveness. By structural and functional comparisons with PmPR10-1.14 promoter, putative wound-responsive elements were potentially identified in the PmPR10-1.13 promoter. In conclusion, PmPR10-1.13 showed properties of a defence-responsive gene, being transcriptionally upregulated upon biotic and abiotic stresses.

Isolation of a family of resistance gene analogue sequences of the nucleotide binding site (NBS) type from Lens species

Most known plant disease-resistance genes (R genes) include in their encoded products domains such as a nucleotide-binding site (NBS) or leucine-rich repeats (LRRs). Sequences with unknown function, but encoding these conserved domains, have been defined as resistance gene analogues (RGAs). The conserved motifs within plant NBS domains make it possible to use degenerate primers and PCR to isolate RGAs. We used degenerate primers deduced from conserved motifs in the NBS domain of NBS-LRR resistance proteins to amplify genomic sequences from Lens species. Fragments from approximately 500-850 bp were obtained. The nucleotide sequence analysis of these fragments revealed 32 different RGA sequences in Lens species with a high similarity (up to 91%) to RGAs from other plants. The predicted amino acid sequences showed that lentil sequences contain all the conserved motifs (P-loop, kinase-2, kinase-3a, GLPL, and MHD) present in the majority of other known plant NBS-LRR resistance genes. Phylogenetic analyses grouped the Lens NBS sequences with the Toll and interleukin-1 receptor (TIR) subclass of NBS-LRR genes, as well as with RGA sequences isolated from other legume species. Using inverse PCR on one putative RGA of lentil, we were able to amplify the flanking regions of this sequence, which contained features found in R proteins.

Rapid and transient activation of transcription of the ERF3 gene by wounding in tobacco leaves: possible involvement of NtWRKYs and autorepression

This study investigated the regulatory mechanism of rapid and transient induction of a transcriptional repressor ERF3 gene by wounding in tobacco (Nicotiana tabacum) leaves. Deletion and mutation analysis of the promoter region have suggested that the proximal W boxes (TGAC(C/T)) and a GCC box, respectively, may be involved in the positive and negative regulation of wound-induced expression of the ERF3 gene. Electrophoretic mobility shift assays indicated that wounding enhanced the specific binding activity of nuclear factors to the W boxes. NtWRKY1, -2, and -4, which are tobacco group I WRKYs, interacted specifically with the W boxes and activated transcription via the W boxes. On the other hand, deletion of the GCC box from NsERF3 promoter-GUS reporter gene caused a delay in down-regulation of transcription after wound induction. In addition, ERF3 repressed transcription via the NsERF3 promoter activated by NtWRKYs. These results suggest the possible involvement of NtWRKYs and autorepression in the rapid and transient expression of the ERF3 gene by wounding.

Ten Rice Peroxidases Redundantly Respond to Multiple Stresses Including Infection with Rice Blast Fungus

Class III plant peroxidases are believed to function in diverse physiological processes including disease resistance and wound response, but predicted low substrate specificities and the presence of 70 or more isoforms have made it difficult to define a specific physiological function(s) for each gene. To select pathogen-responsive POX genes, we analyzed the expression profiles of 22 rice POX genes after infection with rice blast fungus. The expression of 10 POX genes among the 22 genes was induced after fungal inoculation in both compatible and incompatible hosts. Seven of the 10 POX genes were expressed at higher levels in the incompatible host than in the compatible host 6-24 h after inoculation by which time no fungus-induced lesions have appeared. Organ-specific expression and stress-induced expression by wounding and treatment with probenazole, an agrichemical against blast fungus, jasmonic acid, salicylic acid and 1-aminocyclopropane-1-carboxylate, a precursor of ethylene, indicated that rice POXs have individual characteristics and can be classified into several types. A comparison of the amino acid sequences of POXs showed that multiple isoforms with a high sequence similarity respond to stress in different or similar ways. Such redundant responses of POX genes may guarantee POX activities that are necessary for self-defense in plant tissues against environmental stresses including pathogen infection.

Ectopic expression of a horseradish peroxidase enhances growth rate and increases oxidative stress resistance in hybrid aspen

We previously demonstrated that overexpression of the horseradish (Armoracia rusticana) peroxidase prxC1a gene stimulated the growth rate of tobacco (Nicotiana tabacum) plants. Here, the cauliflower mosaic virus 35S::prxC1a construct was introduced into hybrid aspen (Populus sieboldii x Populus grandidentata). The growth rate of these transformed hybrid aspen plants was substantially increased under greenhouse conditions. The average stem length of transformed plants was 25% greater than that of control plants. There was no other obvious phenotypic difference between the transformed and control plants. Fast-growing transformed hybrid aspen showed high levels of expression of prxC1a and had elevated peroxidase activities toward guaiacol and ascorbate. However, there was no increase of the endogenous class I ascorbate peroxidase activities in the transformed plants by separate assay and activity staining of native polyacrylamide gel electrophoresis. Furthermore, calli derived from the transformed hybrid aspen grew faster than those from control plants and were resistant to the oxidative stress imposed by hydrogen peroxide. Therefore, enhanced peroxidase activity affects plant growth rate and oxidative stress resistance.

A wound-inducible tobacco peroxidase gene expresses preferentially in the vascular system

A tobacco peroxidase gene tpoxN1 was reported to be expressed within 1 h after wounding in leaves [Hiraga et al. (2000a) Plant Cell Physiol. 41: 165]. We describe here further results on the wound-induced tpoxN1 expression. The quick tpoxN1 induction occurred preferentially in stems and petioles, but was negligible in leaf blades even 8 h after wounding. Induced GUS activity was also detected rapidly after wounding in the stem of transgenic tobacco plants carrying the tpoxN1 promoter::GUS fusion gene, localized mainly in the vascular systems where it was maintained this level for 14 d or more. Strong GUS activity was also found in the petiole and veinlet as well as the epidermal tissue in the stem. Treatment of known inducers for wound-responsive genes such as jasmonate, 1-aminocyclopropane-1-carboxylate, spermine, phytohormones and other stress treatments did not enhance wound-induced tpoxN1 gene expression in stems at all, but rather repressed it in some cases. Studies using metabolic inhibitors suggested that phosphorylation and dephosphorylation of proteins together with de novo protein synthesis are likely to be involved in the wound-induced tpoxN1 expression as well as some other wound-responsive genes. Thus, tpoxN1 is a unique wound-inducible and possible wound-healing gene which is rapidly expressed being maintained for a long time in veins via an unknown wound-signaling pathway(s).

Transcriptional control of lignin biosynthesis by tobacco LIM protein

Lignin is a complex phenolic plant polymer that is essential for mechanical support, defense, and water transport in higher plants. The AC-rich motif, Pal-box is an important cis-acting element for gene expression in phenylpropanoid biosynthesis. We isolated a cDNA clone (Ntlim1) encoding a Pal-box binding protein by Southwestern screening. The deduced amino acid sequence of Ntlim1 is highly similar to members of the LIM protein family that contain a zinc finger motif. Moreover, Ntlim1 had a specific DNA-binding ability and transiently activated transcription of a beta-glucuronidase reporter gene driven by the Pal-box sequence. The results of transient expression assays with tobacco cultured cells showed that fusion proteins between GFP and Ntlim1 can enter nuclei. Transgenic tobacco plants with antisense Ntlim1 showed low levels of transcripts from some key phenylpropanoid pathway genes such as phenylalanine ammonia-lyase, hydroxycinnamate CoA ligase and cinnamyl alcohol dehydrogenase. Furthermore, a greater than 20% reduction in lignin content was observed in transgenic tobacco with antisense Ntlim1.

A large family of class III plant peroxidases

Class III plant peroxidase (POX), a plant-specific oxidoreductase, is one of the many types of peroxidases that are widely distributed in animals, plants and microorganisms. POXs exist as isoenzymes in individual plant species, and each isoenzyme has variable amino acid sequences and shows diverse expression profiles, suggesting their involvement in various physiological processes. Indeed, studies have provided evidence that POXs participate in lignification, suberization, auxin catabolism, wound healing and defense against pathogen infection. Little, however, is known about the signal transduction for inducing expression of the pox genes. Recent studies have provided information on the regulatory mechanisms of wound- and pathogen-induced expression of some pox genes. These studies suggest that pox genes are induced via different signal transduction pathways from those of other known defense-related genes.

Molecular cloning of a soybean class III beta-1,3-glucanase gene that is regulated both developmentally and in response to pathogen infection

We isolated and characterized a soybean gene (SGN1) encoding a basic beta-1,3-glucanase that is a plant class III isoform of beta-1,3-glucanase. The deduced amino acid sequence of the SGN1 gene is similar to that of the PR-Q'b gene, the basic class III beta-1,3-glucanase of tomato. Based on RNA blot hybridization, SGN1 gene expression was detected in all tissues of 4-day old seedlings, but it was present only in root tissue of 30-day old plants. GUS expression analysis carried out in transgenic tobacco plants harboring a SGN1::GUS reporter gene revealed the same expression pattern. Furthermore, the expression of SGN1 was strongly induced by a variety of defense-related signals, such as treatment with H(2)O(2), wounding, or treatment with fungal elicitor prepared from Phytophthora spp as well as inoculation with Pseudomonas syringae. However, the expression level of SGN1 was hardly induced with jasmonate, ethephon and salicylate. Overall the results suggest that the SGN1 may play a role in both plant development and plant defense against pathogen attack.

Functional analysis of tobacco LIM protein Ntlim1 involved in lignin biosynthesis

The AC-rich motif, Pal-box, is an important cis-acting element for gene expression involved in phenylpropanoid biosynthesis. A cDNA clone (Ntlim1) encoding a Pal-box binding protein was isolated by Southwestern screening. The deduced amino acid sequence is highly similar to the members of the LIM protein family that contain a zinc finger motif. Moreover, Ntlim1 had a specific DNA binding ability and transiently activated the transcription of a beta-glucuronidase reporter gene driven by the Pal-box sequence in tobacco protoplasts. The transgenic tobacco plants with antisense Ntlim1 showed low levels of transcripts from some key phenylpropanoid pathway genes such as phenylalanine ammonia-lyase, hydroxycinnamate CoA ligase and cinnamyl alcohol dehydrogenase. Furthermore, a 27% reduction of lignin content was observed in the transgenic tobacco with antisense Ntlim1.

Transgene expression systems in plant, a natural bioreactor

Plants are important resources that have been providing us food from the earliest times. The rapid advances that have taken place in plant genetic engineering have made it possible to modify plants to increase food production and contribute to environmental purification. Transgenic plants are gaining increasing attention from the industry as a natural bioreactor for the production of industrial and chemical products. Useful expression systems based on promoters to optimize transgene expression in plant cells, hold the key to maximizing the potential of this concept of molecular-farming or industrial plants. This review, which is devoted to the use of plants for heterologous protein production, is divided into three parts. First, we introduce the nature of plant promoters and strategies for the isolation of novel promoters. In the second part, various promoters showing high-level constitutive, organ-specific, or inducible expression, are summarized as useful tools for realizing the efficient transcription of transgenes. Finally, problems in the expression of foreign gene in plant cells and future prospects in plant biotechnology are discussed.

Isolation and characterization of the E2F-like gene in plants

The transcription factor E2F regulates the expression of genes involved in the progression of G1/S transition and DNA replication in mammalian cells. We cloned and characterized a cDNA (NtE2F) corresponding to a E2F homolog of tobacco (Nicotiana tabacum). The transcription of NtE2F was induced as cells progressed from G1 to the S phase and expressed much earlier than that of the proliferating cell nuclear antigen (PCNA) gene. We demonstrated that NtE2F can interact with the tobacco retinoblastoma (Rb)-related protein in a yeast two-hybrid assay. To further characterize NtE2F, the trans-activation activity of NtE2F was examined by using a transient assay in the tobacco Bright Yellow-2 (BY-2) cells with NtE2F fused to the DNA-binding domain of the veast transcriptional activator GAL4. NtE2F activated the transcription of the beta-glucuronidase (GUS) reporter gene driven by a cauliflower mosaic virus (CaMV) 35S core promoter containing the GAL4-binding sequence. This is the first report of the identification of a functionally equivalent E2F-like gene in plants.

Transcription factors and their genes in higher plants functional domains, evolution and regulation

A typical plant transcription factor contains, with few exceptions, a DNA-binding region, an oligomerization site, a transcription-regulation domain, and a nuclear localization signal. Most transcription factors exhibit only one type of DNA-binding and oligomerization domain, occasionally in multiple copies, but some contain two distinct types. DNA-binding regions are normally adjacent to or overlap with oligomerization sites, and their combined tertiary structure determines critical aspects of transcription factor activity. Pairs of nuclear localization signals exist in several transcription factors, and basic amino acid residues play essential roles in their function, a property also true for DNA-binding domains. Multigene families encode transcription factors, with members either dispersed in the genome or clustered on the same chromosome. Distribution and sequence analyses suggest that transcription factor families evolved via gene duplication, exon capture, translocation, and mutation. The expression of transcription factor genes in plants is regulated at transcriptional and post-transcriptional levels, while the activity of their protein products is modulated post-translationally. The purpose of this review is to describe the domain structure of plant transcription factors, and to relate this information to processes that control the synthesis and action of these proteins.

A peroxidase gene promoter induced by phytopathogens and methyl jasmonate in transgenic plants

The expression of two closely related peroxidase isogenes, Shpx6a and Shpx6b, of the legume Stylosanthes humilis was studied using isogene-specific reverse transcriptase PCR techniques. Results indicated that transcripts of both genes were rapidly induced following inoculation with the fungal pathogen Colletotrichum gloeosporioides, wounding and treatment with the defense regulator methyl jasmonate (MeJA). In contrast treatment of leaves of S. humilis with abscisic acid (ABA) and salicylic acid (SA) did not induce transcripts of either isogene. A genomic clone containing the Shpx6b gene was isolated and 594 bp of 5' sequence upstream of the translation start was fused in frame to the coding region of the uidA reporter gene and introduced into tobacco. Expression from the Shpx6b promoter in transgenic plants was determined by histochemical staining and quantitative assays of beta-glucuronidase (GUS). In transgenic tobacco, GUS expression was detected in cotyledons, vascular cells of young leaves, anthers, pollen, and the stigma and style. Wounding of the tobacco plants produced very localized GUS staining. Much more extensive staining for GUS was observed following inoculation of tobacco leaves with conidia of the fungal pathogen Cercospora nicotianae and the inoculation of wound sites with mycelium of the Oomycete pathogen Phytophthora parasitica var. nicotianae. Treatment of mature leaves with methyl jasmonate induced GUS activity while treatment with ABA, SA, and H2O2 had no effect. A similar strong induction of GUS activity was measured in young transgenic seedlings germinated on MeJA while some, but much weaker, induction of GUS activity was observed in seedlings treated with SA. The sequence of the promoter contained motifs homologous to putative cis elements in other plant genes responsive to MeJA. The Shpx6b gene is the first plant peroxidase gene shown to be induced by both microbial pathogens and MeJA and its promoter will be useful for investigations of signaling processes during fungal infection and for the expression of foreign gene products at infection sites.

Light regulated transcription in higher plants

Studies on the function of plant promoters have demonstrated the presence of regulatorycis-acting elements that mediate developmental or environmental signals. Analysis of many light-responsive genes showed thatcis-acting elements responsible for light regulated transcription are located within the 5' upstream region. Numerous light responsivecis-acting elements andtrans-acting factors have been identified and characterized. The present article reviews the recent advances in studies of light regulated transcriptional regulation and signal transduction.

Construction of gene expression system in cultured tobacco cells

To construct a gene expression system in cultured tobacco cells, useful regulatory elements of plant genes were studied. The promoter of the horseradish peroxidase gene, prxC2, showed high activity in tobacco cells, and it contained enhancer sequences and a cis element for wound induction. The heat shock promoter of the HSP18.2 gene from A. thaliana had strong activity of transcription when the incubation temperature of tobacco cells was shifted from 25 degrees C to 37 degrees C. These elements could be good candidates for foreign gene expression in tobacco cells.

The G-box: a ubiquitous regulatory DNA element in plants bound by the GBF family of bZIP proteins

The G-box (CACGTG) is a ubiquitous, cis-acting DNA regulatory element found in plant genomes. Proteins known as G-box factors (GBFs) bind to G-boxes in a context-specific manner, mediating a wide variety of gene expression patterns. We suggest that, as for many biological systems, different combinations of these common elements can lead to diversity and specificity in the regulation of plant gene expression.

Molecular cloning and expression analysis of peroxidase genes from wheat

A PCR-based screening approach was used to isolate genomic clones from wheat encoding peroxidase isozymes. Three complete genes (pox1, pox2 and pox4) and one truncated gene (pox3) were characterized. The nucleotide sequences predicted mature proteins of 31 kDa, in which all the highly conserved motifs of secreted plant peroxidases were preserved. The coding regions showed 73-83% DNA sequence identity, with the highest level of similarity noted for the tandemly oriented pox2 and pox3. Expression of respective pox genes in various tissues of wheat was assessed by the RT-PCR technique, which showed that all four genes are active. The primary pox1 mRNA was spliced to remove three introns, whereas processing of the other pox transcripts involved only two intervening sequences. Splicing occurred at consensus GU/AG splice sites except for the first introns of pox1, pox2 and pox4 transcripts, where processing took place at unusual GC donor sites. The RNA analysis suggested that the pox1, pox2 and pox4 genes are predominantly expressed in roots. Lower levels of expression were found for pox4 and pox3 in leaves. Infection of wheat by the powdery mildew fungus selectively induced expression of pox2 in leaves.