The 5'UTR-intron of the Gladiolus polyubiquitin promoter GUBQ1 enhances translation efficiency in Gladiolus and Arabidopsis

In Vitro Culture Technology and Advanced Biotechnology Tools Toward Improvement in Gladiolus (Gladiolus species): Present Scenario and Future Prospects

In the world's flower trade, gladiolus (Gladiolus spp.) is ranked first among bulbous flowers and eighth among cut flowers, with more than 30,000 different cultivars being grown. Mass multiplication and commercialization are restricted by the traditional propagation methods. However, the large-scale proliferation and improvement of the gladiolus have been accomplished with the aid of plant tissue culture and other biotechnological techniques. The current review includes a thorough examination of the growth and development parameters required for successful in vitro gladiolus development as well as cormel formation. Moreover, focus is being given to various techniques and methods such as in vitro cytogenetic stability and modification of chromosome number, in vitro mutagenesis and selection of pest resistance, in vitro identification and selection to develop virus-free germplasm, cryopreservation, synthetic seed technology, identifying virus diseases by RT-PCR, somaclonal variation, and protoplast and somatic hybridization. Molecular markers and their applications for genetic diversity analysis, relationships between different genotypes, and clonal stability analysis in Gladiolus species have been conducted by several research groups worldwide and are also being discussed. The article also covers efforts to enhance the functionality of plant phenotypes through genetic transformation. Future prospects for further improvement of ornamental gladiolus are also explored. Overall, the current review provides insight into the applications of basic and advanced biotechnological tools for gladiolus improvement.

Genome-Wide Comparison and Functional Characterization of HMGR Gene Family Associated with Shikonin Biosynthesis in Lithospermum erythrorhizon

3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), as the rate-limiting enzyme in the mevalonate pathway, is essential for the biosynthesis of shikonin in Lithospermum erythrorhizon. However, in the absence of sufficient data, the principles of a genome-wide in-depth evolutionary exploration of HMGR family members in plants, as well as key members related to shikonin biosynthesis, remain unidentified. In this study, 124 HMGRs were identified and characterized from 36 representative plants, including L. erythrorhizon. Vascular plants were found to have more HMGR family genes than nonvascular plants. The phylogenetic tree revealed that during lineage and species diversification, the HMGRs evolved independently and intronless LerHMGRs emerged from multi-intron HMGR in land plants. Among them, Pinus tabuliformis and L. erythrorhizon had the most HMGR gene duplications, with 11 LerHMGRs most likely expanded through WGD/segmental and tandem duplications. In seedling roots and M9 cultured cells/hairy roots, where shikonin biosynthesis occurs, LerHMGR1 and LerHMGR2 were expressed significantly more than other genes. The enzymatic activities of LerHMGR1 and LerHMGR2 further supported their roles in catalyzing the conversion of HMG-CoA to mevalonate. Our findings provide insight into the molecular evolutionary properties and function of the HMGR family in plants and a basis for the genetic improvement of efficiently produced secondary metabolites in L. erythrorhizon.

Plant Promoters and Terminators for High-Precision Bioengineering

High-precision bioengineering and synthetic biology require fine-tuning gene expression at both transcriptional and posttranscriptional levels. Gene transcription is tightly regulated by promoters and terminators. Promoters determine the timing, tissues and cells, and levels of the expression of genes. Terminators mediate transcription termination of genes and affect mRNA levels posttranscriptionally, e.g., the 3'-end processing, stability, translation efficiency, and nuclear to cytoplasmic export of mRNAs. The promoter and terminator combination affects gene expression. In the present article, we review the function and features of plant core promoters, proximal and distal promoters, and terminators, and their effects on and benchmarking strategies for regulating gene expression.

Genome-Wide Analysis of SAUR Gene Family Identifies a Candidate Associated with Fruit Size in Loquat (Eriobotrya japonica Lindl.)

Fruit size is an important fruit quality trait that influences the production and commodity values of loquats (Eriobotrya japonica Lindl.). The Small Auxin Upregulated RNA (SAUR) gene family has proven to play a vital role in the fruit development of many plant species. However, it has not been comprehensively studied in a genome-wide manner in loquats, and its role in regulating fruit size remains unknown. In this study, we identified 95 EjSAUR genes in the loquat genome. Tandem duplication and segmental duplication contributed to the expansion of this gene family in loquats. Phylogenetic analysis grouped the SAURs from Arabidopsis, rice, and loquat into nine clusters. By analyzing the transcriptome profiles in different tissues and at different fruit developmental stages and comparing two sister lines with contrasting fruit sizes, as well as by functional predictions, a candidate gene (EjSAUR22) highly expressed in expanding fruits was selected for further functional investigation. A combination of Indoleacetic acid (IAA) treatment and virus-induced gene silencing revealed that EjSAUR22 was not only responsive to auxin, but also played a role in regulating cell size and fruit expansion. The findings from our study provide a solid foundation for understanding the molecular mechanisms controlling fruit size in loquats, and also provide potential targets for manipulation of fruit size to accelerate loquat breeding.

Optimization of T-DNA configuration with UBIQUITIN10 promoters and tRNA-sgRNA complexes promotes highly efficient genome editing in allotetraploid tobacco

KEY MESSAGE

Combination of UBIQUITIN10 promoter-directed CAS9 and tRNA-gRNA complexes in gene-editing assay induces 80% mutant phenotype with a knockout of the four allelic copies in the T0 generation of allotetraploid tobaccos. While gene-editing methodologies, such as CRISPR-Cas9, have been developed and successfully used in many plant species, their use remains challenging, because they most often rely on stable or transient transgene expression. Regrettably, in all plant species, transformation causes epigenetic effects such as gene silencing and variable transgene expression. Here, UBIQUITIN10 promoters from several plant species were characterized and showed their capacity to direct high levels of transgene expression in transient and stable transformation assays, which in turn was used to improve the selection process of regenerated transformants. Furthermore, we compared various sgRNAs delivery systems and showed that the combination of UBIQUITIN10 promoters and tRNA-sgRNA complexes produced 80% mutant phenotype with a complete knockout of the four allelic copies, while the remaining 20% exhibited weaker phenotype, which suggested partial allelic knockout, in the T0 generation of the allotetraploid Nicotiana tabacum. These data provide valuable information to optimize future designs of gene editing constructs for plant research and crop improvement and open the way for valuable gene editing projects in non-model Solanaceae species.

Genome-Scale Computational Identification and Characterization of UTR Introns in Atalantia buxifolia

Accumulated evidence has shown that CDS introns (CIs) play important roles in regulating gene expression. However, research on UTR introns (UIs) is limited. In this study, UIs (including 5′UTR and 3′UTR introns (5UIs and 3UIs)) were identified from the Atalantia buxifolia genome. The length and nucleotide distribution characteristics of both 5UIs and 3UIs and the distributions of cis-acting elements and transcription factor binding sites (TFBSs) in 5UIs were investigated. Moreover, PageMan enrichment analysis was applied to show the possible roles of transcripts containing UIs (UI-Ts). In total, 1077 5UIs and 866 3UIs were identified from 897 5UI-Ts and 670 3UI-Ts, respectively. Among them, 765 (85.28%) 5UI-Ts and 527 (78.66%) 3UI-Ts contained only one UI, and 94 (6.38%) UI-Ts contained both 5UI and 3UI. The UI density was lower than that of CDS introns, but their mean and median intron sizes were ~2 times those of the CDS introns. The A. buxifolia 5UIs were rich in gene-expression-enhancement-related elements and contained many TFBSs for BBR-BPC, MIKC_MADS, AP2 and Dof TFs, indicating that 5UIs play a role in regulating or enhancing the expression of downstream genes. Enrichment analysis revealed that UI-Ts involved in ‘not assigned’ and ‘RNA’ pathways were significantly enriched. Noteworthily, 119 (85.61%) of the 3UI-Ts were genes encoding pentatricopeptide (PPR) repeat-containing proteins. These results will be helpful for the future study of the regulatory roles of UIs in A. buxifolia.

Identification of transcription factors interacting with a 1274 bp promoter of MaPIP1;1 which confers high-level gene expression and drought stress Inducibility in transgenic Arabidopsis thaliana

BACKGROUND

Drought stress can severely affect plant growth and crop yield. The cloning and identification of drought-inducible promoters would be of value for genetically-based strategies to improve resistance of crops to drought.

RESULTS

Previous studies showed that the MaPIP1;1 gene encoding an aquaporin is involved in the plant drought stress response. In this study, the promoter pMaPIP1;1, which lies 1362 bp upstream of the MaPIP1;1 transcriptional initiation site, was isolated from the banana genome..And the transcription start site(A) is 47 bp before the ATG. To functionally validate the promoter, various lengths of pMaPIP1;1 were deleted and fused to GUS to generate pMaPIP1;1::GUS fusion constructs that were then transformed into Arabidopsis to generate four transformants termed M-P1, M-P2, M-P3 and M-P4.Mannitol treatment was used to simulate drought conditions. All four transformants reacted well to mannitol treatment. M-P2 (- 1274 bp to - 1) showed the highest transcriptional activity among all transgenic Arabidopsis tissues, indicating that M-P2 was the core region of pMaPIP1;1. This region of the promoter also confers high levels of gene expression in response to mannitol treatment. Using M-P2 as a yeast one-hybrid bait, 23 different transcription factors or genes that interacted with MaPIP1;1 were screened. In an dual luciferase assay for complementarity verification, the transcription factor MADS3 positively regulated MaPIP1;1 transcription when combined with the banana promoter. qRT-PCR showed that MADS3 expression was similar in banana leaves and roots under drought stress. In banana plants grown in 45% soil moisture to mimic drought stress, MaPIP1;1 expression was maximized, which further demonstrated that the MADS3 transcription factor can synergize with MaPIP1;1.

CONCLUSIONS

Together our results revealed that MaPIP1;1 mediates molecular mechanisms associated with drought responses in banana, and will expand our understanding of how AQP gene expression is regulated. The findings lay a foundation for genetic improvement of banana drought resistance.

Genome-Wide Identification and Characterization of UTR-Introns of Citrus sinensis

Introns exist not only in coding sequences (CDSs) but also in untranslated regions (UTRs) of a gene. Recent studies in animals and model plants such as Arabidopsis have revealed that the UTR-introns (UIs) are widely presented in most genomes and involved in regulation of gene expression or RNA stability. In the present study, we identified introns at both 5'UTRs (5UIs) and 3'UTRs (3UIs) of sweet orange genes, investigated their size and nucleotide distribution characteristics, and explored the distribution of cis-elements in the UI sequences. Functional category of genes with predicted UIs were further analyzed using GO, KEGG, and PageMan enrichment. In addition, the organ-dependent splicing and abundance of selected UI-containing genes in root, leaf, and stem were experimentally determined. Totally, we identified 825 UI- and 570 3UI-containing transcripts, corresponding to 617 and 469 genes, respectively. Among them, 74 genes contain both 5UI and 3UI. Nucleotide distribution analysis showed that 5UI distribution is biased at both ends of 5'UTR whiles 3UI distribution is biased close to the start site of 3'UTR. Cis- elements analysis revealed that 5UI and 3UI sequences were rich of promoter-enhancing related elements, indicating that they might function in regulating the expression through them. Function enrichment analysis revealed that genes containing 5UI are significantly enriched in the RNA transport pathway. While, genes containing 3UI are significantly enriched in splicesome. Notably, many pentatricopeptide repeat-containing protein genes and the disease resistance genes were identified to be 3UI-containing. RT-PCR result confirmed the existence of UIs in the eight selected gene transcripts whereas alternative splicing events were found in some of them. Meanwhile, qRT-PCR result showed that UIs were differentially expressed among organs, and significant correlation was found between some genes and their UIs, for example: The expression of VPS28 and its 3UI was significantly negative correlated. This is the first report about the UIs in sweet orange from genome-wide level, which could provide evidence for further understanding of the role of UIs in gene expression regulation.

Tree Bark Phenols Regulate the Physiological and Biochemical Performance of Gladiolus Flowers

The postharvest physiology of cut flowers is largely dependent on vase life, which is the maximum number of days before flower senescence. The use of tree bark extracts (major forest plant residues), as an eco-friendly and natural antioxidant preservative in holding solutions, is a novel tool for extending flower longevity. The morphological, physiological, biochemical, and genetic responses of Gladiolus grandiflorus cut spikes to Magnolia acuminata and Taxus cuspidata bark extracts as additives in holding solutions were investigated. G. grandiflorus subjected to bark extracts as well as catechin and protocatechuic acid (main phenols) displayed significant increased longevity (up to 18 days), an increased number of open florets, and increased floret fresh weight. Increases in the relative water content, leaf chlorophyll, carotenoids, soluble sugars, and protein content were observed in addition to a reduction in microbial growth in the cut spikes. Gas exchange parameters were higher in the bark extract treatments than in the controls. Higher antioxidant activities were detected and associated with increased superoxide dismutase and catalase enzyme activities and reduced H2O2 accumulation. The bark extract treatments associated with reduced expression of GgCyP1 (produces cysteine protease) and increased expression of both GgDAD1 (defends against apoptotic activity) and GgEXPA1 (regulates petal expansion). Several mechanisms were implicated in these effects, including maintenance of water content, enhanced management of reactive oxygen species (ROS), increased sugar and protein composition, and control of microbial growth. Thus, bark extracts and isolated phenols could be developed as an eco-friendly, non-toxic, and cost-effective natural preservative for cut gladiolus flowers.

Identification of a 119-bp Promoter of the Maize Sulfite Oxidase Gene (ZmSO) That Confers High-Level Gene Expression and ABA or Drought Inducibility in Transgenic Plants

Drought adversely affects crop growth and yields. The cloning and characterization of drought- or abscisic acid (ABA)-inducible promoters is of great significance for their utilization in the genetic improvement of crop resistance. Our previous studies have shown that maize sulfite oxidase (SO) has a sulfite-oxidizing function and is involved in the drought stress response. However, the promoter of the maize SO gene has not yet been characterized. In this study, the promoter (ZmSOPro, 1194 bp upstream region of the translation initiation site) was isolated from the maize genome. The in-silico analysis of the ZmSOPro promoter identified several cis-elements responsive to the phytohormone ABA and drought stress such as ABA-responsive element (ABRE) and MYB binding site (MBS), besides a number of core cis-acting elements, such as TATA-box and CAAT-box. A 5′ RACE (rapid amplification of cDNA ends) assay identified an adenine residue as the transcription start site of the ZmSO. The ZmSOPro activity was detected by β-glucuronidase (GUS) staining at nearly all developmental stages and in most plant organs, except for the roots in transgenic Arabidopsis. Moreover, its activity was significantly induced by ABA and drought stress. The 5′-deletion mutant analysis of the ZmSOPro in tobacco plants revealed that a 119-bp fragment in the ZmSOPro (upstream of the transcription start site) is a minimal region, which is required for its high-level expression. Moreover, the minimal ZmSOPro was significantly activated by ABA or drought stress in transgenic plants. Further mutant analysis indicated that the MBS element in the minimal ZmSOPro region (119 bp upstream of the transcription start site) is responsible for ABA and drought-stress induced expression. These results improve our understanding of the transcriptional regulation mechanism of the ZmSO gene, and the characterized 119-bp promoter fragment could be an ideal candidate for drought-tolerant gene engineering in both monocot and dicot crops.

The exon-intron gene structure upstream of the initiation codon predicts translation efficiency

Introns in mRNA leaders are common in complex eukaryotes, but often overlooked. These introns are spliced out before translation, leaving exon-exon junctions in the mRNA leaders (leader EEJs). Our multi-omic approach shows that the number of leader EEJs inversely correlates with the main protein translation, as does the number of upstream open reading frames (uORFs). Across the five species studied, the lowest levels of translation were observed for mRNAs with both leader EEJs and uORFs (29%). This class of mRNAs also have ribosome footprints on uORFs, with strong triplet periodicity indicating uORF translation. Furthermore, the positions of both leader EEJ and uORF are conserved between human and mouse. Thus, the uORF, in combination with leader EEJ predicts lower expression for nearly one-third of eukaryotic proteins.

Synthetic introns help identify sequences in the 5' UTR intron of the Glycine max polyubiquitin (Gmubi) promoter that give increased promoter activity

MAIN CONCLUSION

Specific sequences within the leader intron of a soybean polyubiquitin gene stimulated gene expression when placed either within a synthetic intron or upstream of a core promoter. The intron in the 5' untranslated region of the soybean polyubiquitin promoter, Gmubi, seems to contribute to the high activity of this promoter. To identify the stimulatory sequences within the intron, ten different sequential intronic sequences of 40 nt were isolated, cloned as tetrameric repeats and placed upstream of a minimal cauliflower mosaic virus 35S (35S) core promoter, which was used to control expression of the green fluorescent protein. Intron fragment tetramers were also cloned within a modified, native intron, creating a Synthetic INtron Cassette (SINC), which was then placed downstream of Gmubi and 35S core promoters. Intron fragment tetramers and SINC constructs were evaluated using transient expression in lima bean cotyledons and stable expression in soybean hairy roots. Intron fragments, used as tetramers upstream of the 35S core promoter, yielded up to 80 times higher expression than the core promoter in transient expression analyses and ten times higher expression in stably transformed hairy roots. Tetrameric intronic fragments, cloned downstream of the Gmubi and 35S core promoters and within the synthetic intron, also yielded increased transient and stable GFP expression that was up to 4 times higher than Gmubi alone and up to 40 times higher than the 35S core promoter alone. These intron fragments contain sequences that seem to act as promoter regulatory elements and may contribute to the increased expression observed with this native strong promoter. Intron regulatory elements and synthetic introns may provide additional tools for increasing transgene expression in plants.

Intron-Mediated Enhancement: A Tool for Heterologous Gene Expression in Plants?

Many plant promoters were characterized and used for transgene expression in plants. Even though these promoters drive high levels of transgene expression in plants, the expression patterns are rarely constitutive but restricted to some tissues and developmental stages. In terms of crop improvement not only the enhancement of expression per se but, in particular, tissue-specific and spatial expression of genes plays an important role. Introns were used to boost expression in transgenic plants in the field of crop improvement for a long time. However, the mechanism behind this so called intron-mediated enhancement (IME) is still largely unknown. This review highlights the complexity of IME on the levels of its regulation and modes of action and gives an overview on IME methodology, examples in fundamental research and models of proposed mechanisms. In addition, the application of IME in heterologous gene expression is discussed.

Current status and biotechnological advances in genetic engineering of ornamental plants

Cut flower markets are developing in many countries as the international demand for cut flowers is rapidly growing. Developing new varieties with modified characteristics is an important aim in floriculture. Production of transgenic ornamental plants can shorten the time required in the conventional breeding of a cultivar. Biotechnology tools in combination with conventional breeding methods have been used by cut flower breeders to change flower color, plant architecture, post-harvest traits, and disease resistance. In this review, we describe advances in genetic engineering that have led to the development of new cut flower varieties.

Identification of a 467 bp Promoter of Maize Phosphatidylinositol Synthase Gene (ZmPIS) Which Confers High-Level Gene Expression and Salinity or Osmotic Stress Inducibility in Transgenic Tobacco

Salinity and drought often affect plant growth and crop yields. Cloning and identification of salinity and drought stress inducible promoters is of great significance for their use in the genetic improvement of crop resistance. Previous studies showed that phosphatidylinositol synthase is involved in plant salinity and drought stress responses but its promoter has not been characterized by far. In the study, the promoter (pZmPIS, 1834 bp upstream region of the translation initiation site) was isolated from maize genome. To functionally validate the promoter, eight 5' deletion fragments of pZmPIS in different lengths were fused to GUS to produce pZmPIS::GUS constructs and transformed into tobacco, namely PZ1-PZ8. The transcription activity and expression pattern obviously changed when the promoter was truncated. Previous studies have demonstrated that NaCl and PEG treatments are usually used to simulate salinity and drought treatments. The results showed that PZ1-PZ7 can respond well upon NaCl and PEG treatments, while PZ8 not. PZ7 (467 bp) displayed the highest transcription activity in all tissues of transgenic tobacco amongst 5' deleted promoter fragments, which corresponds to about 20 and 50% of CaMV35S under normal and NaCl or PEG treatment, respectively. This implied that PZ7 is the core region of pZmPIS which confers high-level gene expression and NaCl or PEG inducible nature. The 113 bp segment between PZ7 and PZ8 (-467 to -355 bp) was considered as the key sequence for ZmPIS responding to NaCl or PEG treatment. GUS transient assay in tobacco leaves showed that this segment was sufficient for the NaCl or PEG stress response. Bioinformatic analysis revealed that the 113 bp sequence may contain new elements that are crucial for ZmPIS response to NaCl or PEG stress. These results promote our understanding on transcriptional regulation mechanism of ZmPIS and the characterized PZ7 promoter fragment would be an ideal candidate for the overexpression of drought and salinity responsive gene to improve crop resistance.

Copy Number Variation of Cytokinin Oxidase Gene Tackx4 Associated with Grain Weight and Chlorophyll Content of Flag Leaf in Common Wheat

As the main pigment in photosynthesis, chlorophyll significantly affects grain filling and grain weight of crop. Cytokinin (CTK) can effectively increase chlorophyll content and chloroplast stability, but it is irreversibly inactivated by cytokinin oxidase (CKX). In this study, therefore, twenty-four pairs of primers were designed to identify variations of wheat CKX (Tackx) genes associated with flag leaf chlorophyll content after anthesis, as well as grain weight in 169 recombinant inbred lines (RIL) derived from Triticum aestivum Jing 411 × Hongmangchun 21. Results indicated variation of Tackx4, identified by primer pair T19-20, was proven to significantly associate with chlorophyll content and grain weight in the RIL population. Here, two Tackx4 patterns were identified: one with two co-segregated fragments (Tackx4-1/Tackx4-2) containing 618 bp and 620 bp in size (as in Jing 411), and another with no PCR product. The two genotypes were designated as genotype-A and genotype-B, respectively. Grain weight and leaf chlorophyll content at 5~15 days after anthesis (DAA) were significantly higher in genotype-A lines than those in genotype-B lines. Mapping analysis indicated Tackx4 was closely linked to Xwmc169 on chromosome 3AL, as well as co-segregated with a major quantitative trait locus (QTL) for both grain weight and chlorophyll content of flag leaf at 5~15 DAA. This QTL explained 8.9~22.3% phenotypic variations of the two traits across four cropping seasons. Among 102 wheat varieties, a third genotype of Tackx4 was found and designated as genotype-C, also having two co-segregated fragments, Tackx4-2 and Tackx4-3 (615bp). The sequences of three fragments, Tackx4-1, Tackx4-2, and Tackx4-3, showed high identity (>98%). Therefore, these fragments could be considered as different copies at Tackx4 locus on chromosome 3AL. The effect of copy number variation (CNV) of Tackx4 was further validated. In general, genotype-A contains both significantly higher grain weight and flag leaf chlorophyll content at 5~15 DAA than those in genotype-B and genotype-C, among 102 varieties under various environments.

Identification of a Novel Allele of TaCKX6a02 Associated with Grain Size, Filling Rate and Weight of Common Wheat

Cytokinin oxidase (CKX) plays a crucial role in plant growth and development by reversibly inactivating cytokinin (CTK). Twenty-four primer pairs, designed from ESTs of the TaCKX genes family of common wheat, were used to identify their allelic variations associated with grain size, weight, and filling rate in 169 recombinant inbred lines (RIL) derived from Jing 411 × Hongmangchun 21. TaCKX6a02, a member of TaCKX gene family, amplified by primer pair T31–32, showed a close association with grain traits in this RIL population. Statistical analysis indicated that allelic variation of TaCKX6a02 had significant correlation with grain size, weight, and filling rate (GFR; P < 0.001) under varied environments. The TaCKX6a02-D1a allele from Jing411 significantly increased grain size, weight and grain filling rate, compared with TaCKX6a02-D1b from Hongmangchun 21. TaCKX6a02 was located on chromosome 3DS in the interval of Xbarc1119 and Xbarc1162, with a genetic distance of 1.4 cM. The location was further confirmed using Chinese Spring nulli–tetrasomic lines. A major QTL (quantitative trait locus) tightly linked to TaCKX6a02 was detected in the RIL population, explaining 17.1~38.2% of phenotype variations for grain size, weight, GFRmax and GFRmean in different environments. In addition, significant effects of variations of TaCKX6a02 on grain weight and GFR were further validated by association analysis among 102 wheat varieties in two cropping seasons. 12.8~35.1% of phenotypic variations were estimated for these genotypes. A novel 29-bp InDel behind the stop codon was detected by DNA sequence analysis between the two alleles of TaCKX6a02-D1. The gene-specific marker, TKX3D, was designed according to the novel variation, and can be used in marker-assisted selection (MAS) for grain size, weight, and GFR in common wheat.

Isolation and characterization of an ubiquitin extension protein gene (JcUEP) promoter from Jatropha curcas

The JcUEP promoter is active constitutively in the bio-fuel plant Jatropha curcas , and is an alternative to the widely used CaMV35S promoter for driving constitutive overexpression of transgenes in Jatropha. Well-characterized promoters are required for transgenic breeding of Jatropha curcas, a biofuel feedstock with great potential for production of bio-diesel and bio-jet fuel. In this study, an ubiquitin extension protein gene from Jatropha, designated JcUEP, was identified to be ubiquitously expressed. Thus, we isolated a 1.2 kb fragment of the 5' flanking region of JcUEP and evaluated its activity as a constitutive promoter in Arabidopsis and Jatropha using the β-glucuronidase (GUS) reporter gene. As expected, histochemical GUS assay showed that the JcUEP promoter was active in all Arabidopsis and Jatropha tissues tested. We also compared the activity of the JcUEP promoter with that of the cauliflower mosaic virus 35S (CaMV35S) promoter, a well-characterized constitutive promoter conferring strong transgene expression in dicot species, in various tissues of Jatropha. In a fluorometric GUS assay, the two promoters showed similar activities in stems, mature leaves and female flowers; while the CaMV35S promoter was more effective than the JcUEP promoter in other tissues, especially young leaves and inflorescences. In addition, the JcUEP promoter retained its activity under stress conditions in low temperature, high salt, dehydration and exogenous ABA treatments. These results suggest that the plant-derived JcUEP promoter could be an alternative to the CaMV35S promoter for driving constitutive overexpression of transgenes in Jatropha and other plants.

Investigating the role of introns in the regulation of regenerating gene 1 expression

Gastrin is a hormone that physiologically regulates gastric acid secretion and contributes to the maintenance of gastric epithelial architecture by regulating the expression of genes such as regenerating gene 1 (Reg1). Reg1 is involved in gastric carcinogenesis as an antiapoptotic factor. The current study explores the molecular mechanism of gastrin-regulated Reg1 expression in human gastric cancer cells. In total, five intron fragments of the Reg1 gene were cloned by polymerase chain reaction and inserted into luciferase reporter vector pGL3 to construct intron-luciferase reporter vectors. After confirmation by Xho I/Hind III digestion and DNA sequencing, the five constructs were transfected into the SGC7901 gastric cancer cell line. The luciferase activity of the cells transfected with each of the five constructs was detected following incubation without or with gastrin. The five intron fragments of Reg1 were also randomly labeled with digoxin as a probe, and nuclear proteins of gastric cancer cells were extracted following treatment with or without gastrin. Southwestern blotting was subsequently performed to detect transcription factors that bind to the introns. The results indicated that the luciferase activity was significantly higher in cells transfected with recombinant vectors containing introns 2, 3, 4 or 5 than that in the cells transfected with an empty vector (P<0.05). However, no statistically significant difference in luciferase activity was identified between cells transfected with pGL3-intron 1 and those transfected with pGL3-Basic (P>0.05). Following incubation with gastrin, no significant difference was identified (P>0.05). The five introns of Reg1 can bind a number of transcription factors and gastrin may affect this interaction. Introns 2–5 of Reg1 potentially have transcriptional control over gene expression in gastric cancer cells. In conclusion, gastrin may regulate the expression of the Reg1 gene via the interaction of the introns by binding to the transcription factors.

Genome-wide analysis of the Hsp20 gene family in soybean: comprehensive sequence, genomic organization and expression profile analysis under abiotic and biotic stresses

BACKGROUND

The Hsp20 genes are associated with stress caused by HS and other abiotic factors, but have recently been found to be associated with the response to biotic stresses. These genes represent the most abundant class among the HSPs in plants, but little is known about this gene family in soybean. Because of their apparent multifunctionality, these proteins are promising targets for developing crop varieties that are better adapted to biotic and abiotic stresses. Thus, in the present study an in silico identification of GmHsp20 gene family members was performed, and the genes were characterized and subjected to in vivo expression analysis under biotic and abiotic stresses.

RESULTS

A search of the available soybean genome databases revealed 51 gene models as potential GmHsp20 candidates. The 51 GmHsp20 genes were distributed across a total of 15 subfamilies where a specific predicted secondary structure was identified. Based on in vivo analysis, only 47 soybean Hsp20 genes were responsive to heat shock stress. Among the GmHsp20 genes that were potentials HSR, five were also cold-induced, and another five, in addition to one GmAcd gene, were responsive to Meloidogyne javanica infection. Furthermore, one predicted GmHsp20 was shown to be responsive only to nematode infection; no expression change was detected under other stress conditions. Some of the biotic stress-responsive GmHsp20 genes exhibited a divergent expression pattern between resistant and susceptible soybean genotypes under M. javanica infection. The putative regulatory elements presenting some conservation level in the GmHsp20 promoters included HSE, W-box, CAAT box, and TA-rich elements. Some of these putative elements showed a unique occurrence pattern among genes responsive to nematode infection.

CONCLUSIONS

The evolution of Hsp20 family in soybean genome has most likely involved a total of 23 gene duplications. The obtained expression profiles revealed that the majority of the 51 GmHsp20 candidates are induced under HT, but other members of this family could also be involved in normal cellular functions, unrelated to HT. Some of the GmHsp20 genes might be specialized to respond to nematode stress, and the predicted promoter structure of these genes seems to have a particular conserved pattern related to their biological function.