Sugar-responsible elements in the promoter of a gene for beta-amylase of sweet potato

ACRE, a class of AP2/ERF transcription factors, activates the expression of sweet potato ß-amylase and sporamin genes through the sugar-responsible element CMSRE-1

Sugars, synthesized by photosynthesis in source organs, are loaded and utilized as an energy source and carbon skeleton in sink organs, and also known to be important signal molecules regulating gene expression in higher plants. The expression of genes coding for sporamin and β-amylase, the two most abundant proteins in storage roots of sweet potato, is coordinately induced by sugars. We previously reported on the identification of the carbohydrate metabolic signal-responsible element-1 (CMSRE-1) essential for the sugar-responsible expression of two genes. However, transcription factors that bind to this sequence have not been identified. In this study, we performed yeast one-hybrid screening using the sugar-responsible minimal promoter region of the ß-amylase gene as bait and a library composed only transcription factor cDNAs of Arabidopsis. Two clones, named Activator protein binding to CMSRE-1 (ACRE), encoding AP2/ERF transcription factors were isolated. ACRE showed transactivation activity of the sugar-responsible minimal promoter in a CMSRE-1-dependent manner in Arabidopsis protoplasts. Electric mobility shift assay (EMSA) using recombinant proteins and transient co-expression assay in Arabidopsis protoplasts revealed that ACRE could actually act to the CMSRE-1. Among the DEHYDRATION -RESPONSIVE ELEMENT BINDING FACTOR (DREB) subfamily, almost all homologs including ACRE, could act on the DRE, while only three ACREs could act to the CMSRE-1. Moreover, ACRE-homologs of Japanese morning glory also have the same property of DNA-binding preference and transactivation activity through the CMSRE-1. These findings suggested that ACRE plays an important role in the mechanism regulating the sugar-responsible gene expression through the CMSRE-1 conserved across plant species.

Comparative Analysis of Saccharification Characteristics of Different Type Sweetpotato Cultivars

As an important characteristic crop in China, sweetpotato plays an important role in the intake and supplement of nutrients. The saccharification characteristics of sweetpotato determine the edible quality and processing type. Exploring the saccharification characteristics of sweetpotato is of great significance to the selection of processing materials and the formation mechanism of service quality, but there are few relevant studies. A comparison study of two high saccharification varieties (Y25 and Z13) and one low saccharification variety (X27) was conducted to analyze their storage roots physical and chemical properties. The results show that the dry matter content, starch, and amylose content of Y25 and Z13 were significantly different from those of X27. Furthermore, the total amylase activity was significantly higher than that of X27. On the other hand, the starch gelatinization temperature was significantly lower than that of X27. The starch reduction in Y25 and Z13 is four times more than that in X27, and the maltose content of Y25 and Z13 is more than two times that of X27. Finally, the scores of sensory evaluation and physiological sweetness were significantly higher than those of X27. The results provide a theoretical basis for understanding the saccharification characteristics of sweetpotato varieties and are of guiding significance for the selection of sweetpotato parents.

Tomato SlSTK is involved in glucose response and regulated by the ubiquitin ligase SlSINA4

Glucose signaling plays an essential role in plant growth, development and stress response. Previous studies have shown that STOREKEEPER (STK) is a new class of DNA binding protein that regulates patatin expression in potato tubers and confers elevated sensitivity to glucose response in Arabidopsis thaliana. However, the biological functions of STK gene in tomato (Solanum lycopersicum) have not been studied. Here, we characterized the tomato SlSTK and determined its role in glucose signaling. The SlSTK protein was localized in the nucleus and the expression of the SlSTK gene was induced by the glucose treatment. Overexpression of SlSTK in tomato enhanced glucose sensitivity, as manifested by reduced seed germination rate and arrested growth at the early seedling stage. In contrast, the SlSTK-knockout plants generated via the clustered regularly interspaced short palindromic repeats (CRISPR) - CRISPR-associated protein 9 (CRISPR-Cas9) technique attenuated the sensitivity to glucose. In addition, SlSTK was ubiquitinated in plant cells and interacted with the tomato ubiquitin ligase SEVEN IN ABSENTIA4 (SlSINA4) that degrades SlSTK in a ligase-dependent manner. Taken together, these results suggest that SlSTK is involved in glucose signaling and its stability is regulated by the ubiquitin ligase SlSINA4.

Harnessing tissue-specific genome editing in plants through CRISPR/Cas system: current state and future prospects

In a nutshell, tissue-specific CRISPR/Cas genome editing is the most promising approach for crop improvement which can bypass the hurdle associated with constitutive GE such as off target and pleotropic effects for targeted crop improvement. CRISPR/Cas is a powerful genome-editing tool with a wide range of applications for the genetic improvement of crops. However, the constitutive genome editing of vital genes is often associated with pleiotropic effects on other genes, needless metabolic burden, or interference in the cellular machinery. Tissue-specific genome editing (TSGE), on the other hand, enables researchers to study those genes in specific cells, tissues, or organs without disturbing neighboring groups of cells. Until recently, there was only limited proof of the TSGE concept, where the CRISPR-TSKO tool was successfully used in Arabidopsis, tomato, and cotton, laying a solid foundation for crop improvement. In this review, we have laid out valuable insights into the concept and application of TSGE on relatively unexplored areas such as grain trait improvement under favorable or unfavorable conditions. We also enlisted some of the prominent tissue-specific promoters and described the procedure of their isolation with several TSGE promoter expression systems in detail. Moreover, we highlighted potential negative regulatory genes that could be targeted through TSGE using tissue-specific promoters. In a nutshell, tissue-specific CRISPR/Cas genome editing is the most promising approach for crop improvement which can bypass the hurdle associated with constitutive GE such as off target and pleotropic effects for targeted crop improvement.

Regulation of β-amylase synthesis: a brief overview

BACKGROUND

The major activity of β-amylase (BMY) is the production of maltose by the hydrolytic degradation of starch. BMY is found to be produced by some plants and few microorganisms only. The industrial importance of the enzyme warrants its application in a larger scale with the help of genetic engineering, for which the regulatory mechanism is to be clearly understood.

RESULTS AND CONCLUSION

In plants, the activities of BMY are regulated by various environmental stimuli including stress of drought, cold and heat. In vascular plant, Arabidopsis sp. the enzyme is coded by nine BAM genes, whereas in most bacteria, BMY enzymes are coded by the spoII gene family. The activities of these genes are in turn controlled by various compounds. Production and inhibition of the microbial BMY is regulated by the activation and inactivation of various BAM genes. Various types of transcriptional regulators associated with the plant- BMYs regulate the production of BMY enzyme. The enhancement in the expression of such genes reflects evolutionary significance. Bacterial genes, on the other hand, as exemplified by Bacillus sp and Clostridium sp, clearly depict the importance of a single regulatory gene, the absence or mutation of which totally abolishes the BMY activity.

Comparison and Characterization of a Cell Wall Invertase Promoter from Cu-Tolerant and Non-Tolerant Populations of Elsholtzia haichowensis

Cell wall invertase (CWIN) activity and the expression of the corresponding gene were previously observed to be significantly elevated in a Cu-tolerant population of Elsholtzia haichowensis relative to a non-tolerant population under copper stress. To understand the differences in CWIN gene regulation between the two populations, their CWIN promoter β-glucuronidase (GUS) reporter vectors were constructed. GUS activity was measured in transgenic Arabidopsis in response to copper, sugar, and phytohormone treatments. Under the copper treatment, only the activity of the CWIN promoter from the Cu-tolerant population was slightly increased. Glucose and fructose significantly induced the activity of CWIN promoters from both populations. Among the phytohormone treatments, only salicylic acid induced significantly higher (p < 0.05) activity of the Cu-tolerant CWIN promoter relative to the non-tolerant promoters. Analysis of 5′-deletion constructs revealed that a 270-bp promoter fragment was required for SA induction of the promoter from the Cu-tolerant population. Comparison of this region in the two CWIN promoters revealed that it had 10 mutation sites and contained CAAT-box and W-box cis-elements in the Cu-tolerant promoter only. This work provides insights into the regulatory role of SA in CWIN gene expression and offers an explanation for differences in CWIN expression between E. haichowensis populations.

Regulation of color transition in purple tea (Camellia sinensis)

Comparative proteomics and metabolomics study of juvenile green, light purple and dark purple leaf to identify key proteins and metabolites that putatively govern color transition in Camellia sinensis. Color transition from juvenile green to dark purple leaf in Camellia sinensis is a complex process and thought to be regulated by an intricate balance of genes, proteins and metabolites expression. A molecular-level understanding of proteins and metabolites expression is needed to define metabolic process underpinning color transition in C. sinensis. Here, purple leaf growth of C. sinensis cultivar was divided into three developmental stages viz. juvenile green (JG), light purple (LP) and dark purple (DP) leaf. Scanning electron microscope (SEM) analysis revealed a clear morphological variation such as cell size, shape and texture as tea leaf undergoing color transition. Proteomic and metabolomic analyses displayed the temporal changes in proteins and metabolites that occur in color transition process. In total, 211 differentially expressed proteins (DEPs) were identified presumably involved in secondary metabolic processes particularly, flavonoids/anthocyanin biosynthesis, phytohormone regulation, carbon and nitrogen assimilation and photosynthesis, among others. Subcellular localization of three candidate proteins was further evaluated by their transient expression in planta. Interactome study revealed that proteins involved in primary metabolism, precursor metabolite, photosynthesis, phytohormones, transcription factor and anthocyanin biosynthesis were found to be interact directly or indirectly and thus, regulate color transition from JG to DP leaf. The present study not only corroborated earlier findings but also identified novel proteins and metabolites that putatively govern color transition in C. sinensis. These findings provide a platform for future studies that may be utilized for metabolic engineering/molecular breeding in an effort to develop more desirable traits.

Transcriptomic Analysis of Verbena bonariensis Leaves Under Low-Temperature Stress

Verbena bonariensis is a valuable plant for both ornament and flower border. As a major constraint, low temperature affects the growing development and survival of V. bonariensis. However, there are few systematic studies in terms of molecular mechanism on the tolerance of low temperature in V. bonariensis. In this study, Illumina sequencing technology was applied to analyze the cold resistance mechanism of plants. Six cDNA libraries were obtained from two samples of two groups, the cold-treated group and the control group. A total of 271,920 unigenes were produced from 406,641 assembled transcripts. Among these, 19,003 differentially expressed genes (DEGs) (corrected p-value <0.01, |log2(fold change) | >3) were obtained, including 9852 upregulated and 9151 downregulated genes. The antioxidant enzyme system, photosynthesis, plant hormone signal transduction, fatty acid metabolism, starch and sucrose metabolism pathway, and transcription factors were analyzed. Based on these results, series of candidate genes related to cold stress were screened out and discussed. The physiological indexes related to response mechanism of low temperature were tested. Eleven upregulated DEGs were validated by Quantitative Real-time PCR. In this study, we provided the transcriptome sequence resource of V. bonariensis and used these data to realize its molecular mechanism under cold stress. The results contributed to valuable clues for genetic studies and helped to screen candidate genes for cold-resistance breeding.

A non-tandem CCCH-type zinc-finger protein, IbC3H18, functions as a nuclear transcriptional activator and enhances abiotic stress tolerance in sweet potato

CCCH-type zinc-finger proteins play essential roles in regulating plant development and stress responses. However, the molecular and functional properties of non-tandem CCCH-type zinc-finger (non-TZF) proteins have been rarely characterized in plants. Here, we report the biological and molecular characterization of a sweet potato non-TZF gene, IbC3H18. We show that IbC3H18 exhibits tissue- and abiotic stress-specific expression, and could be effectively induced by abiotic stresses, including NaCl, polyethylene glycol (PEG) 6000, H2 O2 and abscisic acid (ABA) in sweet potato. Accordingly, overexpression of IbC3H18 led to increased, whereas knock-down of IbC3H18 resulted in decreased tolerance of sweet potato to salt, drought and oxidation stresses. In addition, IbC3H18 functions as a nuclear transcriptional activator and regulates the expression of a range of abiotic stress-responsive genes involved in reactive oxygen species (ROS) scavenging, ABA signaling, photosynthesis and ion transport pathways. Moreover, our data demonstrate that IbC3H18 physically interacts with IbPR5, and that overexpression of IbPR5 enhances salt and drought tolerance in transgenic tobacco plants. Collectively, our data indicate that IbC3H18 functions in enhancing abiotic stress tolerance in sweet potato, which may serve as a candidate gene for use in improving abiotic stress resistance in crops.

Transcriptomic and evolutionary analyses of white pear (Pyrus bretschneideri) β-amylase genes reveals their importance for cold and drought stress responses

β-amylase (BAM) genes play essential roles in plant abiotic stress responses. Although the genome of Chinese white pear (Pyrus bretschneideri) has recently been made available, knowledge regarding the BAM family in pear, including gene function, evolutionary history and patterns of gene expression remains limited. In this study, we identified 17 PbBAMs in the pear genome. Of these, 12 PbBAM members were mapped onto 9 chromosomes and 5 PbBAM genes were located on scaffold contigs. Based on gene structure, protein motif analysis, and the topology of the phylogenetic tree of the PbBAM family, we classified member genes into 4 groups. All PbBAM genes were found to contain typical glycosyl hydrolysis 14 domain motifs. Interfamilial comparisons revealed that the phylogenetic relationships of BAM genes in other Rosaceae species were similar those found in pear. We also found that whole-genome duplication (WGD)/segmental duplication events played critical roles in the expansion of the BAM family. Next, we used transcriptomic data to study gene expression during the response of drought and low temperate responses, and found that genes in Group B were related to drought and cold stress. We identified four PbBAM genes associated with abiotic stress in Pear. Finally, by analyzing co-expression networks and co-regulatory genes, we found that PbBAM1a and PbBAM1b were associated with the pear abiotic stress response.

The Sugar-Signaling Hub: Overview of Regulators and Interaction with the Hormonal and Metabolic Network

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

The Sugar-Signaling Hub: Overview of Regulators and Interaction with the Hormonal and Metabolic Network

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

A soluble starch synthase I gene, IbSSI, alters the content, composition, granule size and structure of starch in transgenic sweet potato

Soluble starch synthase I (SSI) is a key enzyme in the biosynthesis of plant amylopectin. In this study, the gene named IbSSI, was cloned from sweet potato, an important starch crop. A high expression level of IbSSI was detected in the leaves and storage roots of the sweet potato. Its overexpression significantly increased the content and granule size of starch and the proportion of amylopectin by up-regulating starch biosynthetic genes in the transgenic plants compared with wild-type plants (WT) and RNA interference plants. The frequency of chains with degree of polymerization (DP) 5-8 decreased in the amylopectin fraction of starch, whereas the proportion of chains with DP 9-25 increased in the IbSSI-overexpressing plants compared with WT plants. Further analysis demonstrated that IbSSI was responsible for the synthesis of chains with DP ranging from 9 to 17, which represents a different chain length spectrum in vivo from its counterparts in rice and wheat. These findings suggest that the IbSSI gene plays important roles in determining the content, composition, granule size and structure of starch in sweet potato. This gene may be utilized to improve the content and quality of starch in sweet potato and other plants.

OsWRKY51, a rice transcription factor, functions as a positive regulator in defense response against Xanthomonas oryzae pv. oryzae

OsWRKY51 functions as a positive transcriptional regulator in defense signaling against Xanthomonas oryzae pv. oryzae by direct DNA binding to the promoter of defense related gene, OsPR10a. OsWRKY51 in rice (Oryza sativa L.) is induced by exogenous salicylic acid (SA) and inoculation with Xanthomonas oryzae pv. oryzae (Xoo). To examine the role of OsWRKY51 in the defense response of rice, we generated OsWRKY51 overexpressing and underexpressing transgenic rice plants. OsWRKY51-overexpressing transgenic rice lines were more resistant to Xoo and showed greater expression of defense-related genes than wild-type (WT) plants, while OsWRKY51-underexpressing lines were more susceptible to Xoo and showed less expression of defense-associated genes than WT plants. Transgenic lines overexpressing OsWRKY51 showed growth retardation compared to WT plants. In contrast, transgenic lines underexpressing OsWRKY51 by RNA interference showed similar plant height with WT plants. Transient expression of OsWRKY51-green fluorescent protein fusion protein in rice protoplasts revealed that OsWRKY51 was localized in the nucleus. OsWRKY51 bound to the W-box and WLE1 elements of the OsPR10a promoter. Based on these results, we suggest that OsWRKY51 is a positive transcriptional regulator of defense signaling and has direct DNA binding ability to the promoter of OsPR10a, although it is reported to be a negative regulator in GA signaling.

Intronic Sequence Regulates Sugar-Dependent Expression of Arabidopsis thaliana Production of Anthocyanin Pigment-1/MYB75

Sucrose-specific regulation of gene expression is recognized as an important signaling response, distinct from glucose, which serves to modulate plant growth, metabolism, and physiology. The Arabidopsis MYB transcription factor Production of Anthocyanin Pigment-1 (PAP1) plays a key role in anthocyanin biosynthesis and expression of PAP1 is known to be regulated by sucrose. Sucrose treatment of Arabidopsis seedlings led to a 20-fold induction of PAP1 transcript, which represented a 6-fold increase over levels in glucose-treated seedlings. The PAP1 promoter was not sufficient for conferring a sucrose response to a reporter gene and did not correctly report expression of PAP1 in plants. Although we identified 3 putative sucrose response elements in the PAP1 gene, none were found to be necessary for this response. Using deletion analysis, we identified a 90 bp sequence within intron 1 of PAP1 that is necessary for the sucrose response. This sequence was sufficient for conferring a sucrose response to a minimal promoter: luciferase reporter when present in multiple copies upstream of the promoter. This work lays the foundation for dissecting the sucrose signaling pathway of PAP1 and contributes to understanding the interplay between sucrose signaling, anthocyanin biosynthesis, and stress responses.

Promoter analysis of the sweet potato ADP-glucose pyrophosphorylase gene IbAGP1 in Nicotiana tabacum

KEY MESSAGE

The IbAGP1 gene of sweet potato ( Ipomoea batatas ) encodes the sucrose-inducible small subunit of ADP-glucose pyrophosphorylase. Through expression analysis of 5'-truncations and synthetic forms of the IbAGP1 promoter in transgenic tobacco, we show that SURE-Like elements and W-box elements of the promoter contribute to the sucrose inducibility of this gene. Sweet potato (Ipomoea batatas) contains two genes (IbAGP1 and IbAGP2) encoding the catalytically active small subunits of ADP-glucose pyrophosphorylase, an enzyme with an important role in regulating starch synthesis in higher plants. Previous studies have shown that IbAGP1 is expressed in the storage roots, leaves, and stem tissues of sweet potato, and its transcript is strongly induced by applying sucrose exogenously to detached leaves. To investigate the tissue-specific expression of the IbAGP1 promoter, a series of 5'-truncated promoters extending from bases -1913, -1598, -1298, -1053, -716, and -286 to base +75 were used to drive the expression of the β-glucuronidase reporter gene (GUS) in tobacco plants (Nicotiana tabacum). Histochemical and fluorometric GUS assays showed that (1) GUS expression driven by the longest fragment (1989 bp) of the IbAGP1 promoter was detected in vegetative tissues (roots, stems, leaves), (2) fragments extending to -1053 or beyond retained strong GUS expression in roots, stems, and leaves, whereas further 5'-deletions resulted in considerable reduction in GUS activity, and (3) the series of 5'-truncated promoters responded differently to exogenously applied sucrose. The 1989-bp IbAGP1 promoter contains five sequences (two AATAAAA, one AATAAAAAA, and two AATAAATAAA) that are similar to sucrose-responsive elements (SURE). These SURE-Like sequences are found at nucleotide positions -1273, -1239, -681, -610, and -189. Moreover, putative W-box elements are found at positions -1985, -1434, -750, and -578. Synthetic promoters containing tandem repeats of the 4X SURE-Like or 4X W-box upstream from a minimal CaMV35S promoter-GUS fusion showed significant expression in transgenic tobacco in response to exogenous sucrose. These results show that SURE-Like elements and W-box elements of the IbAGP1 promoter contribute to the sucrose inducibility of this gene.

ß-amylase1 mutant Arabidopsis plants show improved drought tolerance due to reduced starch breakdown in guard cells

In plants, drought stress is a major growth limiting factor causing cell water loss through open stomata. In this study, guard cell-specific transcripts from drought-stressed Arabidopsis plants were analysed and a down-regulation of β-amylase 1 (BAM1) was found. In previous studies, BAM1 was shown to be involved in stomatal starch degradation under ambient conditions. Impaired starch breakdown of bam1 mutant plants was accompanied by decreased stomatal opening. Here, it is shown that drought tolerance of bam1 mutant plants is improved as compared with wild-type controls. Microarray analysis of stomata-specific transcripts from bam1 mutant plants revealed a significant down-regulation of genes encoding aquaporins, auxin- and ethylene-responsive factors, and cell-wall modifying enzymes. This expression pattern suggests that reduced water uptake and limited cell wall extension are associated with the closed state of stomata of bam1 mutant plants. Together these data suggest that regulation of stomata-specific starch turnover is important for adapting stomata opening to environmental needs and its breeding manipulation may result in drought tolerant crop plants.

Identification and validation of promoters and cis-acting regulatory elements

Studies of promoters that largely regulate gene expression at the transcriptional level are crucial for improving our basic understanding of gene regulation and will expand the toolbox of available promoters for use in plant biotechnology. In this review, we present a comprehensive analysis of promoters and their underlying mechanisms in transcriptional regulation, including epigenetic marks and chromatin-based regulation. Large-scale prediction of promoter sequences and their contributing cis-acting elements has become routine due to recent advances in transcriptomic technologies and genome sequencing of several plants. However, predicted regulatory sequences may or may not be functional and demonstration of the contribution of the element to promoter activity is essential for confirmation of regulatory sequences. Synthetic promoters and introns provide useful approaches for functional validation of promoter sequences. The development and improvement of gene expression tools for rapid, efficient, predictable, and high-throughput analysis of promoter components will be critical for confirmation of the functional regulatory element sequences identified through transcriptomic and genomic analyses.

A novel role for Arabidopsis CBL1 in affecting plant responses to glucose and gibberellin during germination and seedling development

Glucose and phytohormones such as abscisic acid (ABA), ethylene, and gibberellin (GA) coordinately regulate germination and seedling development. However, there is still inadequate evidence to link their molecular roles in affecting plant responses. Calcium acts as a second messenger in a diverse range of signal transduction pathways. As calcium sensors unique to plants, calcineurin B-like (CBL) proteins are well known to modulate abiotic stress responses. In this study, it was found that CBL1 was induced by glucose in Arabidopsis. Loss-of-function mutant cbl1 exhibited hypersensitivity to glucose and paclobutrazol, a GA biosynthetic inhibitor. Several sugar-responsive and GA biosynthetic gene expressions were altered in the cbl1 mutant. CBL1 protein physically interacted with AKINβ1, the regulatory β subunit of the SnRK1 complex which has a central role in sugar signaling. Our results indicate a novel role for CBL1 in modulating responses to glucose and GA signals.

Transgenic sweet potato expressing thionin from barley gives resistance to black rot disease caused by Ceratocystis fimbriata in leaves and storage roots

Black rot of sweet potato caused by pathogenic fungus Ceratocystis fimbriata severely deteriorates both growth of plants and post-harvest storage. Antimicrobial peptides from various organisms have broad range activities of killing bacteria, mycobacteria, and fungi. Plant thionin peptide exhibited anti-fungal activity against C. fimbriata. A gene for barley α-hordothionin (αHT) was placed downstream of a strong constitutive promoter of E12Ω or the promoter of a sweet potato gene for β-amylase of storage roots, and introduced into sweet potato commercial cultivar Kokei No. 14. Transgenic E12Ω:αHT plants showed high-level expression of αHT mRNA in both leaves and storage roots. Transgenic β-Amy:αHT plants showed sucrose-inducible expression of αHT mRNA in leaves, in addition to expression in storage roots. Leaves of E12Ω:αHT plants exhibited reduced yellowing upon infection by C. fimbriata compared to leaves of non-transgenic Kokei No. 14, although the level of resistance was weaker than resistance cultivar Tamayutaka. Storage roots of both E12Ω:αHT and β-Amy:αHT plants exhibited reduced lesion areas around the site inoculated with C. fimbriata spores compared to Kokei No. 14, and some of the transgenic lines showed resistance level similar to Tamayutaka. Growth of plants and production of storage roots of these transgenic plants were not significantly different from non-transgenic plants. These results highlight the usefulness of transgenic sweet potato expressing antimicrobial peptide to reduce damages of sweet potato from the black rot disease and to reduce the use of agricultural chemicals.

In silico analysis of cis-acting regulatory elements in 5' regulatory regions of sucrose transporter gene families in rice (Oryza sativa Japonica) and Arabidopsis thaliana

The regulation of gene expression involves a multifarious regulatory system. Each gene contains a unique combination of cis-acting regulatory sequence elements in the 5' regulatory region that determines its temporal and spatial expression. Cis-acting regulatory elements are essential transcriptional gene regulatory units; they control many biological processes and stress responses. Thus a full understanding of the transcriptional gene regulation system will depend on successful functional analyses of cis-acting elements. Cis-acting regulatory elements present within the 5' regulatory region of the sucrose transporter gene families in rice (Oryza sativa Japonica cultivar-group) and Arabidopsis thaliana, were identified using a bioinformatics approach. The possible cis-acting regulatory elements were predicted by scanning 1.5kbp of 5' regulatory regions of the sucrose transporter genes translational start sites, using Plant CARE, PLACE and Genomatix Matinspector professional databases. Several cis-acting regulatory elements that are associated with plant development, plant hormonal regulation and stress response were identified, and were present in varying frequencies within the 1.5kbp of 5' regulatory region, among which are; A-box, RY, CAT, Pyrimidine-box, Sucrose-box, ABRE, ARF, ERE, GARE, Me-JA, ARE, DRE, GA-motif, GATA, GT-1, MYC, MYB, W-box, and I-box. This result reveals the probable cis-acting regulatory elements that possibly are involved in the expression and regulation of sucrose transporter gene families in rice and Arabidopsis thaliana during cellular development or environmental stress conditions.

Levels and Stability of Expression of Transgenes

It is well known that in a given cell, at a particular time, only a fraction of the entire genome is expressed. Expression of a gene, nuclear, or organellar starts with the onset of transcription and ends in the synthesis of the functional protein. The regulation of gene expression is a complex process that requires the coordinated activity of different proteins and nucleic acids that ultimately determine whether a gene is transcribed, and if transcribed, whether it results in the production of a protein that develops a phenotype. The same also holds true for transgenic crops, which lie at the very core of insert design.

There are multiple checkpoints at which the expression of a gene can be regulated and controlled. Much of the emphasis of studies related to gene expression has been on regulation of gene transcription, and a number of methods are used to effect the control of gene expression. Controlling transgene expression for a commercially valuable trait is necessary to capture its value. Many gene functions are either lethal or produce severe deformity (resulting in loss of value) if over-expressed. Thus, expression of a transgene at a particular site or in response to a particular elicitor is always desirable.

Ethylene response factor TERF1 enhances glucose sensitivity in tobacco through activating the expression of sugar-related genes

Ethylene response factor (ERF) proteins are important plant-specific transcription factors. Increasing evidence shows that ERF proteins regulate plant pathogen resistance, abiotic stress response and plant development through interaction with different stress responsive pathways. Previously, we revealed that overexpression of TERF1 in tobacco activates a cluster gene expression through interacting with GCC box and dehydration responsive element (DRE), resulting in enhanced sensitivity to abscisic acid (ABA) and tolerance to drought, and dark green leaves of mature plants, indicating that TERF1 participates in the integration of ethylene and osmotic responses. Here we further report that overexpression of TERF1 confers sugar response in tobacco. Analysis of the novel isolated tomato TERF1 promoter provides information indicating that there are many cis-acting elements, including sugar responsive elements (SURE) and W box, suggesting that TERF1 might be sugar inducible. This prediction is confirmed by results of reverse transcription-polymerase chain reaction amplification, indicating that transcripts of TERF1 are accumulated in tomato seedlings after application of glucose. Further investigation indicates that the expression of TERF1 in tobacco enhances sensitivity to glucose during seed germination, root and seedling development, showing a decrease of the fresh weight and root elongation under glucose treatment. Detailed investigations provide evidence that TERF1 interacts with the sugar responsive cis-acting element SURE and activates the expression of sugar response genes, establishing the transcriptional regulation of TERF1 in sugar response. Therefore, our results deepen our understanding of the glucose response mediated by the ERF protein TERF1 in tobacco.

Evidence for sugar signalling in the regulation of asparagine synthetase gene expressed in Phaseolus vulgaris roots and nodules

A cDNA clone, designated as PvNAS2, encoding asparagine amidotransferase (asparagine synthetase) was isolated from nodule tissue of common bean (Phaseolus vulgaris cv. Negro Jamapa). Southern blot analysis indicated that asparagine synthetase in bean is encoded by a small gene family. Northern analysis of RNAs from various plant organs demonstrated that PvNAS2 is highly expressed in roots, followed by nodules in which it is mainly induced during the early days of nitrogen fixation. Investigations with the PvNAS2 promoter gusA fusion revealed that the expression of PvNAS2 in roots is confined to vascular bundles and meristematic tissues, while in root nodules its expression is solely localized to vascular traces and outer cortical cells encompassing the central nitrogen-fixing zone, but never detected in either infected or non-infected cells located in the central region of the nodule. PvNAS2 is down-regulated when carbon availability is reduced in nodules, and the addition of sugars to the plants, mainly glucose, boosted its induction, leading to the increased asparagine production. In contrast to PvNAS2 expression and the concomitant asparagine synthesis, glucose supplement resulted in the reduction of ureide content in nodules. Studies with glucose analogues as well as hexokinase inhibitors suggested a role for hexokinase in the sugar-sensing mechanism that regulates PvNAS2 expression in roots. In light of the above results, it is proposed that, in bean, low carbon availability in nodules prompts the down-regulation of the asparagine synthetase enzyme and concomitantly asparagine production. Thereby a favourable environment is created for the efficient transfer of the amido group of glutamine for the synthesis of purines, and then ureide generation.

Molecular cloning, characterization and regulation of two different NADH-glutamate synthase cDNAs in bean nodules

NADH-dependent glutamate synthase (NADH-GOGAT) is a key enzyme in primary ammonia assimilation in Phaseolus vulgaris nodules. Two different types of cDNA clones of PvNADH-GOGAT were isolated from the nodule cDNA libraries. The full-length cDNA clones of PvNADH-GOGAT-I (7.4 kb) and PvNADH-GOGAT-II (7.0 kb), which displayed an 83% homology between them, were isolated using cDNA library screening, 'cDNA library walking' and RT-PCR amplification. Southern analysis employing specific 5' cDNA probes derived from PvNADH-GOGAT-I and PvNADH-GOGAT-II indicated the existence of a single copy of each gene in the bean genome. Both these proteins contain approximately 100 amino acid sequences theoretically addressing each isoenzyme to different subcellular compartments. RT-PCR analysis indicated that PvNADH-GOGAT-II expression is higher than PvNADH-GOGAT-I during nodule development. Expression analysis by RT-PCR also revealed that both of these genes are differentially regulated by sucrose. On the other hand, the expression of PvNADH-GOGAT-I, but not PvNADH-GOGAT-II, was inhibited with nitrogen compounds. In situ hybridization and promoter expression analyses demonstrated that the NADH-GOGAT-I and -II genes are differentially expressed in bean root and nodule tissues. In silico analyses of the NADH-GOGAT promoters revealed the presence of potential cis elements in them that could mediate differential tissue-specific, and sugar and amino acid responsive expression of these genes.

Sugar signalling and gene expression in relation to carbohydrate metabolism under abiotic stresses in plants

Sucrose is required for plant growth and development. The sugar status of plant cells is sensed by sensor proteins. The signal generated by signal transduction cascades, which could involve mitogen-activated protein kinases, protein phosphatases, Ca 2+ and calmodulins, results in appropriate gene expression. A variety of genes are either induced or repressed depending upon the status of soluble sugars. Abiotic stresses to plants result in major alterations in sugar status and hence affect the expression of various genes by down- and up-regulating their expression. Hexokinase-dependent and hexokinase-independent pathways are involved in sugar sensing. Sucrose also acts as a signal molecule as it affects the activity of a proton-sucrose symporter. The sucrose trans-porter acts as a sucrose sensor and is involved in phloem loading. Fructokinase may represent an additional sensor that bypasses hexokinase phosphorylation especially when sucrose synthase is dominant. Mutants isolated on the basis of response of germination and seedling growth to sugars and reporter-based screening protocols are being used to study the response of altered sugar status on gene expression. Common cis-acting elements in sugar signalling pathways have been identified. Transgenic plants with elevated levels of sugars/sugar alcohols like fructans, raffinose series oligosaccharides, trehalose and mannitol are tolerant to different stresses but have usually impaired growth. Efforts need to be made to have transgenic plants in which abiotic stress responsive genes are expressed only at the time of adverse environmental conditions instead of being constitutively synthesized.

Sugar and ABA response pathways and the control of gene expression

Sugars are essential to plant growth and metabolism, both as energy source and as structural components. Sugar production and use are in part controlled at the level of gene expression by the sugars themselves. Responses to sugar are closely integrated with response pathways that indicate environmental conditions such as light and water availability. High sugar levels inhibit seedling development, repress photosynthetic gene expression and induce genes of storage metabolism such as those of starch biosynthesis. Genetic approaches have demonstrated the importance of abscisic acid (ABA) and the transcriptional regulator ABA-insensitive4 (ABI4) in sugar response pathways. Recent analysis of both photosynthetic and starch biosynthetic gene promoters suggest a direct role for ABI4 in their control. The increased understanding of the regulatory promoter elements controlling gene expression, in response to sugar and ABA, allows transcriptional networks to be understood at a molecular level.

Multiple regulatory elements contribute to the vascular-specific expression of the rice HD-Zip gene Oshox1 in Arabidopsis

The primary vascular tissues of plants differentiate from a single precursor tissue, the procambium. The role of upstream regulatory sequences in the transcriptional control of early vascular-specific gene expression is largely unknown. The onset of expression of the rice homeodomain-leucine zipper (HD-Zip) gene Oshox1 marks procambial cells that have acquired their distinctive anatomical features but do not yet display any overt signs of terminal vascular differentiation. The expression pattern of Oshox1 in rice appears to be mainly controlled by the activity of the 1.6 kb upstream promoter region. Here, we show that the Oshox1 promoter directs vascular, auxin- and sucrose-responsive reporter gene expression in Arabidopsis plants in a fashion comparable with that in rice. This is the case not only during normal development but also upon experimental manipulation, suggesting that the cis-acting regulatory elements that are instrumental in Oshox1 expression pattern are conserved between rice and Arabidopsis. Finally, through analysis of reporter gene expression profiles conferred by progressive 5' deletions of the Oshox1 promoter in transgenic Arabidopsis, we have identified upstream regulatory regions required for auxin and sucrose inducibility, and for cell type-, tissue- and organ-specific aspects of Oshox1 expression. Our study suggests that Oshox1 embryonic vascular expression is mainly achieved through suppression of expression in non-vascular tissues.

Two cis-acting regulatory elements are involved in the sucrose-inducible expression of the sporamin gene promoter from sweet potato in transgenic tobacco

In this study, we generated transgenic tobacco plants that express the beta-glucuronidase (GUS) gene under the control of the 305-bp 5'-upstream region of a gene coding for sporamin A of sweet potato. Expression of GUS in excised tobacco leaves was induced by sucrose, mimicking the sugar-inducible expression of the endogenous sporamin genes in sweet potato. Deletion of the sequences extending from position -305 (relative to the transcription start site) to -283 and from -146 to -87 resulted in an approximately 40-fold enhancement in GUS reporter expression. Furthermore, the sequence from -282 to -165 conferred sucrose-inducibility on the -89 core promoter of the Cauliflower Mosaic Virus 35S RNA gene. Analysis of internal deletions, linker scanning and the introduction of base substitutions in the sequence between positions -282 and -165 indicated that sucrose-responsiveness conferred by this region was dependent on the presence of two cis-acting elements, termed CMSREs (carbohydrate metabolite signal responsive elements) 1 and 2, which are separated by a spacer. A sequence similar or identical to the core of CMSRE-1 (TGGACGG) is also present in the promoters of several other sugar-inducible genes, and sequences encopassing the TGGACGG-related motifs from two of these could functionally replace the CMSRE-1 in the truncated sporamin A promoter. These results suggest that the TGGACGG element plays an important role in the sucrose-inducible expression of a group of plant genes.

Symbiotic rhizobium and nitric oxide induce gene expression of non-symbiotic hemoglobin in Lotus japonicus

We characterized the expression profiles of LjHb1 and LjHb2, non-symbiotic hemoglobin (non-sym-Hb) genes of Lotus japonicus. Although LjHb1 and LjHb2 showed 77% homology in their cDNA sequences, LjHb2 is located in a unique position in the phylogenetic tree of plant Hbs. The 5'-upstream regions of both genes contain the motif AAAGGG at a position similar to that in promoters of other non-sym-Hb genes. Expression profiles obtained by using quantitative RT-PCR showed that LjHb1 and LjHb2 were expressed in all tissues of mature plants, and expression was enhanced in mature root nodules. LjHb1 was strongly induced under both hypoxic and cold conditions, and by the application of nitric oxide (NO) donor, whereas LjHb2 was induced only by the application of sucrose. LjHb1 was also induced transiently by the inoculation with the symbiotic rhizobium Mesorhizobium loti MAFF303099. Observations using fluorescence microscopy revealed the induction of LjHb1 expression corresponded to the generation of NO. These results suggest that non-sym-Hb and NO have important roles in stress adaptation and in the early stage of legume-rhizobium symbiosis.

beta-Amylase induction and the protective role of maltose during temperature shock

A number of studies have demonstrated beta-amylase induction in response to abiotic stress. In the present work, a temperature response profile in 5 degrees C increments from 45 degrees C to 0 degrees C showed that induction at temperature extremes was specific for two members of the gene family (BMY7 and BMY8). Both members encode proteins that possess apparent transit peptides for chloroplast stromal localization. However, induction was not observed for other key starch degrading enzymes demonstrating a rather specific response to temperature stress for BMY7 and BMY8. Time course experiments for heat shock at 40 degrees C and cold shock at 5 degrees C showed that beta-amylase induction correlated with maltose accumulation. Maltose has the ability, as demonstrated by in vitro assays, to protect proteins, membranes, and the photosynthetic electron transport chain at physiologically relevant concentrations. Therefore, beta-amylase induction and the resultant maltose accumulation may function as a compatible-solute stabilizing factor in the chloroplast stroma in response to acute temperature stress.

A novel WRKY transcription factor, SUSIBA2, participates in sugar signaling in barley by binding to the sugar-responsive elements of the iso1 promoter

SURE (sugar responsive) is a cis element in plant sugar signaling. The SURE element was reported first for potato, in which it confers sugar responsiveness to the patatin promoter. A SURE binding transcription factor has not been isolated. We have isolated a transcription factor cDNA from barley and purified the corresponding protein. The transcription factor, SUSIBA2 (sugar signaling in barley), belongs to the WRKY proteins and was shown to bind to SURE and W-box elements but not to the SP8a element in the iso1 promoter. Nuclear localization of SUSIBA2 was demonstrated in a transient assay system with a SUSIBA2:green fluorescent protein fusion protein. Exploiting the novel transcription factor oligodeoxynucleotide decoy strategy with transformed barley endosperm provided experimental evidence for the importance of the SURE elements in iso1 transcription. Antibodies against SUSIBA2 were produced, and the expression pattern for susiba2 was determined at the RNA and protein levels. It was found that susiba2 is expressed in endosperm but not in leaves. Transcription of susiba2 is sugar inducible, and ectopic susiba2 expression was obtained in sugar-treated leaves. Likewise, binding to SURE elements was observed for nuclear extracts from sugar-treated but not from control barley leaves. The temporal expression of susiba2 in barley endosperm followed that of iso1 and endogenous sucrose levels, with a peak at approximately 12 days after pollination. Our data indicate that SUSIBA2 binds to the SURE elements in the barley iso1 promoter as an activator. Furthermore, they show that SUSIBA2 is a regulatory transcription factor in starch synthesis and demonstrate the involvement of a WRKY protein in carbohydrate anabolism. Orthologs to SUSIBA2 were isolated from rice and wheat endosperm.