An alternative method of promoter assessment by confocal laser scanning microscopy

Synthetic sub-genomic transcript promoter from Horseradish Latent Virus (HRLV)

We characterized an efficient chimeric sub-genomic transcript promoter from Horseradish Latent Virus, FHS4, active in both dicot and monocot plants, and it could be a potential tool for plant biotechnology. Plant pararetroviruses are a rich source of novel plant promoters widely used for biotechnological applications. Here, we comprehensively characterized a unique sub-genomic transcript (Sgt) promoter of Horseradish Latent Virus (HRLV) and identified a fragment (HS4; - 340 to + 10; 351 bp) that showed the highest expression of reporter genes in both transient and transgenic assays as evidenced by biochemical, histochemical GUS reporter assay and transcript analysis of uidA gene by qRT-PCR. Phylogenetic analysis showed that the HSgt promoter was closely related to the sub-genomic promoter of the Cauliflower Mosaic Virus (CaMV19S). We found that the as-1 element and W-box played an important role in the transcriptional activity of the HS4 promoter. Furthermore, the HS4 promoter was also induced by salicylic acid. Alongside, we enhanced the activity of the HS4 promoter by coupling the enhancer region from Figwort Mosaic Virus (FMV) promoter to the upstream region of it. This hybrid promoter FHS4 was around 1.1 times stronger than the most commonly used promoter, 35S (Cauliflower Mosaic Virus full-length transcript promoter), and was efficient in driving reporter genes in both dicot and monocot plants. Subsequently, transgenic tobacco plants expressing an anti-microbial peptide BrLTP2.1 (Brassica rapa lipid transport protein 2.1), under the control of the FHS4 promoter, were developed. The in vitro anti-fungal assay revealed that the plant-derived BrLTP2.1 protein driven by an FHS4 promoter manifested increased resistance against an important plant fungal pathogen, Alternaria alternata. Finally, we concluded that the FHS4 promoter can be used as an alternative to the 35S promoter and has a high potential to become an efficient tool in plant biotechnology.

Further Characterization of MUAS35SCP and FUAS35SCP Recombinant Promoters and Their Implication in Translational Research

Recombinant promoters are of high value in translational research. Earlier, we developed two recombinant promoters, namely MUAS35SCP and FUAS35SCP, and their transcriptional activities were found to be stronger than that of the most widely used CaMV35S promoter in dicot plants. Presently, we are reporting constitutive expression of both GUS and GFP reporters under the control of these promoters in several monocots, including rice, wheat, and pearl millet. We observed that these promoters could express the reporter genes constitutively, and their expression abilities were almost equal to that of the CaMV35S² promoter. Plant-derived enriched PaDef (Persea americana var. drymifolia defensin) and NsDef2 (Nigella sativa L. defensin 2) antimicrobial peptides expressed under the control of these promoters arrest the growth of devastating phytopathogens like Pseudomonas syringae, Rhodococcus fascians, and Alternaria alternata. We observed that plant-derived NsDef2 and PaDef under control of these promoters showed approximately 80-90% inhibitory activity against Pseudomonas syringae. Hence, these promoters were constitutive and universal, as they can drive the expression of transgenes in both dicot and monocot plants. Alongside, these promoters could become a valuable tool for raising genetically modified plants with in-built resistance toward phytopathogens.

Development of efficient synthetic promoters derived from pararetrovirus suitable for translational research

MAIN CONCLUSION

In this study, useful hybrid promoters were developed for efficient ectopic gene expression in monocot and dicot plants, and they hold strong prominence in both transgenic research and biotech industries. This study deals with developing novel synthetic promoters derived from Rice Tungro Bacilliform Virus (RTBV) and Mirabilis Mosaic Virus (MMV). Despite numerous availability, there is a severe scarcity of promoters universally suitable for monocot and dicot plants. Here, eight chimeric promoter constructs were synthesized as gBlocks gene fragments through domain swapping and hybridization by incorporating important domains of previously characterized RTBV and MMV promoters. The developed promoter constructs were assessed for transient GUS expression in tobacco protoplast (Xanthi Brad) and agro-infiltrated tobacco, petunia, rice and pearl millet. Protoplast expression analysis showed that two promoter constructs, namely pUPMA-RP1-MP1GUS and pUPMA-RP4-MP1GUS exhibited 3.56 and 2.5 times higher activities than that of the CaMV35S promoter. We had observed the similar type of expression patterns of these promoters in agroinfiltration-based transient studies. RP1-MP1 and RP4-MP1 promoters exhibited 1.87- and 1.68-fold increase expression in transgenic tobacco plants; while, a 1.95-fold increase was found in RP1-MP1 transgenic rice plants when compared their activities with CaMV35S promoter. Furthermore, on evaluating these promoter constructs for their expression in the bacterial system, pUPMA-RP1-MP1GFP was found to have the highest GFP expression. Moreover, the promoter construct was also evaluated for its capacity to express the HMP3 gene. Biobeads of encapsulated bacterial cells expressing HMP3 gene under control of the pUPMA-RP4-MP1 promoter were found to reduce 72.9% copper and 29.2% zinc concentration from wastewater. Our results had demonstrated that the developed promoter constructs could be used for translational research in dicot, monocot plants and bacterial systems for efficient gene expression.

RETRACTED: WRKY71 and TGA1a physically interact and synergistically regulate the activity of a novel promoter isolated from Petunia vein-clearing virus

Caulimoviral promoters have become excellent tools for efficient transgene expression in plants. However, the transcriptional framework controlling their systematic regulation is poorly understood. To understand this regulatory mechanism, we extensively studied a novel caulimoviral promoter, PV8 (-163 to +138, 301 bp), isolated from Petunia vein-clearing virus (PVCV). PVCV was found to be Salicylic acid (SA)-inducible and 2.5-3.0 times stronger than the widely used CaMV35S promoter. In silico analysis of the PV8 sequence revealed a unique clustering of two stress-responsive cis-elements, namely, as-11 and W-box1-2, located within a span of 31 bp (-74 to -47) that bound to the TGA1a and WRKY71 plant transcription factors (TFs), respectively. We found that as-1 (TTACG) and W-box (TGAC) elements occupied both TGA1a and WRKY71 on the PV8 backbone. Mutational studies demonstrated that the combinatorial influence of as-1 (-57) and W-box1-2 (-74 and -47) on the PV8 promoter sequence largely modulated its activity. TGA1a and WRKY71 physically interacted and cooperatively enhanced the transcriptional activity of the PV8 promoter. Biotic stress stimuli induced PV8 promoter activity by ~1.5 times. We also established the possible pathogen-elicitor function of AtWRKY71 and NtabWRKY71 TFs. Altogether, this study elucidates the interplay between TFs, biotic stress and caulimoviral promoter function.

Structural characterization of a novel full-length transcript promoter from Horseradish Latent Virus (HRLV) and its transcriptional regulation by multiple stress responsive transcription factors

KEY MESSAGE

The promoter fragment described in this study can be employed for strong transgene expression under both biotic and abiotic stress conditions. Plant-infecting Caulimoviruses have evolved multiple regulatory mechanisms to address various environmental stimuli during the course of evolution. One such mechanism involves the retention of discrete stress responsive cis-elements which are required for their survival and host-specificity. Here we describe the characterization of a novel Caulimoviral promoter isolated from Horseradish Latent Virus (HRLV) and its regulation by multiple stress responsive Transcription factors (TFs) namely DREB1, AREB1 and TGA1a. The activity of full length transcript (Flt-) promoter from HRLV (- 677 to + 283) was investigated in both transient and transgenic assays where we identified H12 (- 427 to + 73) as the highest expressing fragment having ~ 2.5-fold stronger activity than the CaMV35S promoter. The H12 promoter was highly active and near-constitutive in the vegetative and reproductive parts of both Tobacco and Arabidopsis transgenic plants. Interestingly, H12 contains a distinct cluster of cis-elements like dehydration-responsive element (DRE-core; GCCGAC), an ABA-responsive element (ABRE; ACGTGTC) and as-1 element (TGACG) which are known to be induced by cold, drought and pathogen/SA respectively. The specific binding of DREB1, AREB1 and TGA1a to DRE, ABRE and as-1 elements respectively were confirmed by the gel-binding assays using H12 promoter-specific probes. Detailed mutational analysis of the H12 promoter suggested that the presence of DRE-core and as-1 element was indispensable for its activity which was further confirmed by the transactivation assays. Our studies imply that H12 could be a valuable genetic tool for regulated transgene expression under diverse environmental conditions.

Novel Synthetic Promoters from the Cestrum Yellow Leaf Curling Virus

Constitutive promoters direct gene expression uniformly in most tissues and cells at all stages of plant growth and development; they confer steady levels of transgene expression in plant cells and hence their demand is high in plant biology. The gene silencing due to promoter homology can be avoided by either using diverse promoters isolated from different plant and viral genomes or by designing synthetic promoters. The aim of this chapter was to describe the basic protocols needed to develop and analyze novel, synthetic, nearly constitutive promoters from Cestrum yellow leaf curling virus (CmYLCV) through promoter/leader deletion and activating cis-sequence analysis. We also describe the methods to evaluate the strength of the promoters efficiently in various transient expression systems like agroinfiltration assay, gene-gun method, and assay in tobacco protoplasts. Besides, the detailed methods for developing transgenic plants (tobacco and Arabidopsis) for evaluation of the promoter using the GUS reporter gene are also described. The detailed procedure for electrophoretic mobility shift assay (EMSA) coupled with super-shift EMSA analysis are also described for showing the binding of tobacco transcription factor, TGA1a to cis-elements in the CmYLCV distal promoter region.

Functional characterization of a strong bi-directional constitutive plant promoter isolated from cotton leaf curl Burewala virus

Cotton leaf curl Burewala virus (CLCuBuV), belonging to the genus Begomovirus, possesses single-stranded monopartite DNA genome. The bidirectional promoters representing Rep and coat protein (CP) genes of CLCuBuV were characterized and their efficacy was assayed. Rep and CP promoters of CLCuBuV and 35S promoter of Cauliflower mosaic virus (CaMV) were fused with β-glucuronidase (GUS) and green fluorescent protein (GFP) reporter genes. GUS activity in individual plant cells driven by Rep, CP and 35S promoters was estimated using real-time PCR and fluorometric GUS assay. Histochemical staining of GUS in transformed tobacco (Nicotiana tabacum cv. Xanthi) leaves showed highest expression driven by Rep promoter followed by 35S promoter and CP promoter. The expression level of GUS driven by Rep promoter in transformed tobacco plants was shown to be two to four-fold higher than that of 35S promoter, while the expression by CP promoter was slightly lower. Further, the expression of GFP was monitored in agroinfiltrated leaves of N. benthamiana, N. tabacum and cotton (Gossypium hirsutum) plants using confocal laser scanning microscopy. Rep promoter showed strong consistent transient expression in tobacco and cotton leaves as compared to 35S promoter. The strong constitutive CLCuBuV Rep promoter developed in this study could be very useful for high level expression of transgenes in a wide variety of plant cells.

Plant-derived SAC domain of PAR-4 (Prostate Apoptosis Response 4) exhibits growth inhibitory effects in prostate cancer cells

The gene Par-4 (Prostate Apoptosis Response 4) was originally identified in prostate cancer cells undergoing apoptosis and its product Par-4 showed cancer specific pro-apoptotic activity. Particularly, the SAC domain of Par-4 (SAC-Par-4) selectively kills cancer cells leaving normal cells unaffected. The therapeutic significance of bioactive SAC-Par-4 is enormous in cancer biology; however, its large scale production is still a matter of concern. Here we report the production of SAC-Par-4-GFP fusion protein coupled to translational enhancer sequence (5' AMV) and apoplast signal peptide (aTP) in transgenic Nicotiana tabacum cv. Samsun NN plants under the control of a unique recombinant promoter M24. Transgene integration was confirmed by genomic DNA PCR, Southern and Northern blotting, Real-time PCR, and Nuclear run-on assays. Results of Western blot analysis and ELISA confirmed expression of recombinant SAC-Par-4-GFP protein and it was as high as 0.15% of total soluble protein. In addition, we found that targeting of plant recombinant SAC-Par-4-GFP to the apoplast and endoplasmic reticulum (ER) was essential for the stability of plant recombinant protein in comparison to the bacterial derived SAC-Par-4. Deglycosylation analysis demonstrated that ER-targeted SAC-Par-4-GFP-SEKDEL undergoes O-linked glycosylation unlike apoplast-targeted SAC-Par-4-GFP. Furthermore, various in vitro studies like mammalian cells proliferation assay (MTT), apoptosis induction assays, and NF-κB suppression suggested the cytotoxic and apoptotic properties of plant-derived SAC-Par-4-GFP against multiple prostate cancer cell lines. Additionally, pre-treatment of MAT-LyLu prostate cancer cells with purified SAC-Par-4-GFP significantly delayed the onset of tumor in a syngeneic rat prostate cancer model. Taken altogether, we proclaim that plant made SAC-Par-4 may become a useful alternate therapy for effectively alleviating cancer in the new era.

pSiM24 is a novel versatile gene expression vector for transient assays as well as stable expression of foreign genes in plants

We have constructed a small and highly efficient binary Ti vector pSiM24 for plant transformation with maximum efficacy. In the pSiM24 vector, the size of the backbone of the early binary vector pKYLXM24 (GenBank Accession No. HM036220; a derivative of pKYLX71) was reduced from 12.8 kb to 7.1 kb. The binary vector pSiM24 is composed of the following genetic elements: left and right T-DNA borders, a modified full-length transcript promoter (M24) of Mirabilis mosaic virus with duplicated enhancer domains, three multiple cloning sites, a 3'rbcsE9 terminator, replication functions for Escherichia coli (ColE1) and Agrobacterium tumefaciens (pRK2-OriV) and the replicase trfA gene, selectable marker genes for kanamycin resistance (nptII) and ampicillin resistance (bla). The pSiM24 plasmid offers a wide selection of cloning sites, high copy numbers in E. coli and a high cloning capacity for easily manipulating different genetic elements. It has been fully tested in transferring transgenes such as green fluorescent protein (GFP) and β-glucuronidase (GUS) both transiently (agro-infiltration, protoplast electroporation and biolistic) and stably in plant systems (Arabidopsis and tobacco) using both agrobacterium-mediated transformation and biolistic procedures. Not only reporter genes, several other introduced genes were also effectively expressed using pSiM24 expression vector. Hence, the pSiM24 vector would be useful for various plant biotechnological applications. In addition, the pSiM24 plasmid can act as a platform for other applications, such as gene expression studies and different promoter expressional analyses.

Biomass derived from transgenic tobacco expressing the Arabidopsis CESA3ixr1-2 gene exhibits improved saccharification

Studies in Arabidopsis thaliana and Nicotiana tabacum L. variety Samsun NN demonstrated that expression of the CESA3 cellulose synthase gene that contains a point mutation, named ixr1-2, results in greater conversion of plant-derived cellulose to fermentable sugars. The present study was designed to examine the improved enzymatic saccharification efficiency of lignocellulosic biomass of tobacco plants expressing AtCESA3ixr1-2. Three-month-old AtCESA3ixr1-2 transgenic and wild-type tobacco plants (Nicotiana tabacum L. variety Samsun NN) were grown in the presence and absence of isoxaben. Biomass obtained from leaf, stem, and root tissues were analyzed for enzymatic saccharification rates. During enzymatic saccharification, 45% and 25% more sugar was released from transgenic leaf and stem samples, respectively, when compared to the wild-type samples. This gain in saccharification efficiency was achieved without chemical or heat pretreatment. Additionally, leaf and stem biomass from transgenic AtCESA3ixr1-2 requires a reduced amount of enzyme for saccharification compared to biomass from wild-type plants. From a practical standpoint, a similar strategy could be employed to introduce the mutated CESA into energy crops like poplar and switchgrass to improve the efficiency of biomass conversion.

Overexpression of the synthetic chimeric native-T-phylloplanin-GFP genes optimized for monocot and dicot plants renders enhanced resistance to blue mold disease in tobacco (N. tabacum L.)

To enhance the natural plant resistance and to evaluate the antimicrobial properties of phylloplanin against blue mold, we have expressed a synthetic chimeric native-phylloplanin-GFP protein fusion in transgenic Nicotiana tabacum cv. KY14, a cultivar that is highly susceptible to infection by Peronospora tabacina. The coding sequence of the tobacco phylloplanin gene along with its native signal peptide was fused with GFP at the carboxy terminus. The synthetic chimeric gene (native-phylloplanin-GFP) was placed between the modified Mirabilis mosaic virus full-length transcript promoter with duplicated enhancer domains and the terminator sequence from the rbcSE9 gene. The chimeric gene, expressed in transgenic tobacco, was stably inherited in successive plant generations as shown by molecular characterization, GFP quantification, and confocal fluorescent microscopy. Transgenic plants were morphologically similar to wild-type plants and showed no deleterious effects due to transgene expression. Blue mold-sensitivity assays of tobacco lines were performed by applying P. tabacina sporangia to the upper leaf surface. Transgenic lines expressing the fused synthetic native-phyllopanin-GFP gene in the leaf apoplast showed resistance to infection. Our results demonstrate that in vivo expression of a synthetic fused native-phylloplanin-GFP gene in plants can potentially achieve natural protection against microbial plant pathogens, including P. tabacina in tobacco.

Efficient chimeric plant promoters derived from plant infecting viral promoter sequences

In the present study, we developed a set of three chimeric/hybrid promoters namely FSgt-PFlt, PFlt-UAS-2X and MSgt-PFlt incorporating different important domains of Figwort Mosaic Virus sub-genomic transcript promoter (FSgt, -270 to -60), Mirabilis Mosaic Virus sub-genomic transcript promoter (MSgt, -306 to -125) and Peanut Chlorotic Streak Caulimovirus full-length transcript promoter (PFlt-, -353 to +24 and PFlt-UAS, -353 to -49). We demonstrated that these chimeric/hybrid promoters can drive the expression of reporter genes in different plant species including tobacco, Arabidopsis, petunia, tomato and spinach. FSgt-PFlt, PFlt-UAS-2X and MSgt-PFlt promoters showed 4.2, 1.5 and 1.2 times stronger GUS activities compared to the activity of the CaMV35S promoter, respectively, in tobacco protoplasts. Protoplast-derived recombinant promoter driven GFP showed enhanced accumulation compared to that obtained under the CaMV35S promoter. FSgt-PFlt, PFlt-UAS-2X and MSgt-PFlt promoters showed 3.0, 1.3 and 1.0 times stronger activities than the activity of the CaMV35S² (a modified version of the CaMV35S promoter with double enhancer domain) promoter, respectively, in tobacco (Nicotiana tabacum, var. Samsun NN). Alongside, we observed a fair correlation between recombinant promoter-driven GUS accumulation with the corresponding uidA-mRNA level in transgenic tobacco. Histochemical (X-gluc) staining of whole transgenic seedlings and fluorescence images of ImaGene Green™ treated floral parts expressing the GUS under the control of recombinant promoters also support above findings. Furthermore, we confirmed that these chimeric promoters are inducible in the presence of 150 μM salicylic acid (SA) and abscisic acid (ABA). Taken altogether, we propose that SA/ABA inducible chimeric/recombinant promoters could be used for strong expression of gene(s) of interest in crop plants.

Development of an intra-molecularly shuffled efficient chimeric plant promoter from plant infecting Mirabilis mosaic virus promoter sequence

We developed an efficient chimeric promoter, MUASMSCP, with enhanced activity and salicylic acid (SA)/abscisic acid (ABA) inducibility, incorporating the upstream activation sequence (UAS) of Mirabilis mosaic virus full-length transcript (MUAS, -297 to -38) to the 5' end of Mirabilis mosaic virus sub-genomic transcript (MSCP, -306 to -125) promoter-fragment containing the TATA element. We compared the transient activity of the MUASMSCP promoter in tobacco/Arabidopsis protoplasts and in whole plant (Petunia hybrida) with the same that obtained from CaMV35S and MUAS35SCP promoters individually. The MUASMSCP promoter showed 1.1 and 1.5 times stronger GUS-activities over that obtained from MUAS35SCP and CaMV35S promoters respectively, in tobacco (Xanthi Brad) protoplasts. In transgenic tobacco (Nicotiana tabacum, var. Samsun NN), the MUASMSCP promoter showed 1.1 and 2.2 times stronger activities than MUAS35SCP and CaMV35S(2) promoters respectively. We observed a fair correlation between MUASMSCP-, MUAS35SCP- and CaMV35S(2)-driven GUS activities with the corresponding uidA-mRNA level in transgenic plants. X-gluc staining of transgenic germinating seed-sections and whole seedlings also support above findings. Protein-extracts made from tobacco protoplasts expressing GFP and human-IL-24 genes driven individually by the MUASMSCP promoter showed enhanced expression of the reporters compared to that obtained from the CaMV35S promoter. Furthermore, MUASMSCP-driven protoplast-derived human IL-24 showed enhanced cell inhibitory activity in DU-145 prostate cancer cells compared to that obtained from the CaMV35S promoter. We propose chimeric MUASMSCP promoter developed in the study could be useful for strong constitutive expression of transgenes in both plant/animal cells and it may become an efficient substitute for CaMV35S/CaMV35S(2) promoter.

An intergenic region shared by At4g35985 and At4g35987 in Arabidopsis thaliana is a tissue specific and stress inducible bidirectional promoter analyzed in transgenic arabidopsis and tobacco plants

On chromosome 4 in the Arabidopsis genome, two neighboring genes (calmodulin methyl transferase At4g35987 and senescence associated gene At4g35985) are located in a head-to-head divergent orientation sharing a putative bidirectional promoter. This 1258 bp intergenic region contains a number of environmental stress responsive and tissue specific cis-regulatory elements. Transcript analysis of At4g35985 and At4g35987 genes by quantitative real time PCR showed tissue specific and stress inducible expression profiles. We tested the bidirectional promoter-function of the intergenic region shared by the divergent genes At4g35985 and At4g35987 using two reporter genes (GFP and GUS) in both orientations in transient tobacco protoplast and Agro-infiltration assays, as well as in stably transformed transgenic Arabidopsis and tobacco plants. In transient assays with GFP and GUS reporter genes the At4g35985 promoter (P85) showed stronger expression (about 3.5 fold) compared to the At4g35987 promoter (P87). The tissue specific as well as stress responsive functional nature of the bidirectional promoter was evaluated in independent transgenic Arabidopsis and tobacco lines. Expression of P85 activity was detected in the midrib of leaves, leaf trichomes, apical meristemic regions, throughout the root, lateral roots and flowers. The expression of P87 was observed in leaf-tip, hydathodes, apical meristem, root tips, emerging lateral root tips, root stele region and in floral tissues. The bidirectional promoter in both orientations shows differential up-regulation (2.5 to 3 fold) under salt stress. Use of such regulatory elements of bidirectional promoters showing spatial and stress inducible promoter-functions in heterologous system might be an important tool for plant biotechnology and gene stacking applications.

Manipulating cellulose biosynthesis by expression of mutant Arabidopsis proM24::CESA3(ixr1-2) gene in transgenic tobacco

Manipulation of the cellulose biosynthetic machinery in plants has the potential to provide insight into plant growth, morphogenesis and to create modified cellulose for anthropogenic use. Evidence exists that cellulose microfibril structure and its recalcitrance to enzymatic digestion can ameliorated via mis-sense mutation in the primary cell wall-specific gene AtCELLULOSE SYNTHASE (CESA)3. This mis-sense mutation has been identified based on conferring drug resistance to the cellulose inhibitory herbicide isoxaben. To examine whether it would be possible to introduce mutant CESA alleles via a transgenic approach, we overexpressed a modified version of CESA3, AtCESA3(ixr1-2) derived from Arabidopsis thaliana L. Heynh into a different plant family, the Solanceae dicotyledon tobacco (Nicotiana tabacum L. variety Samsun NN). Specifically, a chimeric gene construct of CESA3(ixr1-2) , codon optimized for tobacco, was placed between the heterologous M24 promoter and the rbcSE9 gene terminator. The results demonstrated that the tobacco plants expressing M24-CESA3(ixr1-2) displayed isoxaben resistance, consistent with functionality of the mutated AtCESA3(ixr1-2) in tobacco. Secondly, during enzymatic saccharification, transgenic leaf- and stem-derived cellulose is 54%-66% and 40%-51% more efficient, respectively, compared to the wild type, illustrating translational potential of modified CESA loci. Moreover, the introduction of M24-AtCESA3(ixr1-2) caused aberrant spatial distribution of lignified secondary cell wall tissue and a reduction in the zone occupied by parenchyma cells.

Development of an efficient bi-directional promoter with tripartite enhancer employing three viral promoters

We have developed a novel bi-directional promoter (FsFfCBD) by placing two heterogeneous core-promoters from the Figwort mosaic virus sub-genomic transcript promoter (FsCP, -69 to +31) and Cauliflower mosaic virus 35S promoter (CCP, -89 to +1) respectively on upstream (5') and downstream (3') ends of a tri-hybrid enhancer (FsEFfECE), in reverse orientation. The FsEFfECE domain encompasses three heterologous enhancer fragments from Figwort mosaic virus sub-genomic transcript promoter (FsE, 101 bp, -70 to -170), Figwort mosaic virus full-length transcript promoter (FfE, 196 bp, -249 to -54) and Cauliflower mosaic virus 35S promoter (CE, 254 bp, -343 to -90). The bi-directional nature of the FsFfCBD promoter (coupled to GFP and GUS) was established both in transient systems (onion epidermal cells and tobacco protoplasts) and transgenic plant (Nicotiana tabacum samsun NN) by monitoring the simultaneous expression of GFP and GUS employing fluorescence (for GFP) and biochemical (for GUS) based assays. In transgenic plants, the FsFfCBD promoter was found to be 6.8 and 2.5 times stronger than two parent promoters; Fs and FfC respectively. The bi-directional compound promoter FsFfCBD, composed of three heterologous enhancers with enhanced activity could become a valuable additional tool for efficient plant metabolic engineering and molecular pharming.

Development of vascular tissue and stress inducible hybrid-synthetic promoters through dof-1 motifs rearrangement

A Caulimovirus-based hybrid-promoter, EFCFS, was derived by fusing the distal region (-227 to -54, FUAS) of Figwort mosaic virus full-length transcript promoter (F20) with the core promoter (-151 to +12, FS3CP) domain of Figwort mosaic virus sub-genomic transcript promoter (FS3). The hybrid-promoter (EFCFS) showed enhanced activity compared to the CaMV35S, F20 and FS3 promoters; while it showed equivalent activity with that of the CAMV35S(2) promoter in both transient protoplast (Nicotiana tabacum cv. Xanthi Brad) and transgenic plants (Nicotiana tabacum; Samsun NN). Further, we have engineered the EFCFS promoter sequence by inserting additional copies of the stress-inducible 'AAAG' cis-motif (Dof-1) to generate a set of three hybrid-synthetic promoters namely; EFCFS-HS-1, EFCFS-HS-2 and EFCFS-HS-3-containing 10, 11 and 13 'AAAG' motif, respectively. Transgenic plants expressing these hybrid synthetic promoters coupled to the GUS reporter were developed and their transcriptional activities were compared with F20, FS3, 35S and 35S(2) promoters, respectively. The relative levels of uidA-mRNA accumulation in transgenic plants driven by above promoters individually were compared by qRT-PCR. Localization of GUS reporter activity in plant tissue was assayed by histochemical approach. CLSM-based study revealed that hybrid-synthetic promoters namely; EFCFS-HS-1, EFCFS-HS-2 and EFCFS-HS-3 showed enhanced activity in vascular tissue compared to the CaMV35S promoter. In the presence of abiotic stress elicitors, salicylic acid and jasmonic acid, the EFCFS-HS-1 promoters showed enhanced activity compared to the 35S promoter. Newly derived hybrid-synthetic promoter/s with enhanced activity and stress inducibility could become efficient tools for advancement of plant biotechnology.

Development and functional analysis of novel genetic promoters using DNA shuffling, hybridization and a combination thereof

BACKGROUND

Development of novel synthetic promoters with enhanced regulatory activity is of great value for a diverse range of plant biotechnology applications.

METHODOLOGY

Using the Figwort mosaic virus full-length transcript promoter (F) and the sub-genomic transcript promoter (FS) sequences, we generated two single shuffled promoter libraries (LssF and LssFS), two multiple shuffled promoter libraries (LmsFS-F and LmsF-FS), two hybrid promoters (FuasFScp and FSuasFcp) and two hybrid-shuffled promoter libraries (LhsFuasFScp and LhsFSuasFcp). Transient expression activities of approximately 50 shuffled promoter clones from each of these libraries were assayed in tobacco (Nicotiana tabacum cv. Xanthi) protoplasts. It was observed that most of the shuffled promoters showed reduced activity compared to the two parent promoters (F and FS) and the CaMV35S promoter. In silico studies (computer simulated analyses) revealed that the reduced promoter activities of the shuffled promoters could be due to their higher helical stability. On the contrary, the hybrid promoters FuasFScp and FSuasFcp showed enhanced activities compared to F, FS and CaMV 35S in both transient and transgenic Nicotiana tabacum and Arabidopsis plants. Northern-blot and qRT-PCR data revealed a positive correlation between transcription and enzymatic activity in transgenic tobacco plants expressing hybrid promoters. Histochemical/X-gluc staining of whole transgenic seedlings/tissue-sections and fluorescence images of ImaGene Green™ treated roots and stems expressing the GUS reporter gene under the control of the FuasFScp and FSuasFcp promoters also support the above findings. Furthermore, protein extracts made from protoplasts expressing the human defensin (HNP-1) gene driven by hybrid promoters showed enhanced antibacterial activity compared to the CaMV35S promoter.

SIGNIFICANCE/CONCLUSION

Both shuffled and hybrid promoters developed in the present study can be used as molecular tools to study the regulation of ectopic gene expression in plants.

Development of useful recombinant promoter and its expression analysis in different plant cells using confocal laser scanning microscopy

BACKGROUND

Designing functionally efficient recombinant promoters having reduced sequence homology and enhanced promoter activity will be an important step toward successful stacking or pyramiding of genes in a plant cell for developing transgenic plants expressing desired traits(s). Also basic knowledge regarding plant cell specific expression of a transgene under control of a promoter is crucial to assess the promoter's efficacy.

METHODOLOGY/PRINCIPAL FINDINGS

We have constructed a set of 10 recombinant promoters incorporating different up-stream activation sequences (UAS) of Mirabilis mosaic virus sub-genomic transcript (MS8, -306 to +27) and TATA containing core domains of Figwort mosaic virus sub-genomic transcript promoter (FS3, -271 to +31). Efficacies of recombinant promoters coupled to GUS and GFP reporter genes were tested in tobacco protoplasts. Among these, a 369-bp long hybrid sub-genomic transcript promoter (MSgt-FSgt) showed the highest activity in both transient and transgenic systems. In a transient system, MSgt-FSgt was 10.31, 2.86 and 2.18 times more active compared to the CaMV35S, MS8 and FS3 promoters, respectively. In transgenic tobacco (Nicotiana tabaccum, var. Samsun NN) and Arabidopsis plants, the MSgt-FSgt hybrid promoter showed 14.22 and 7.16 times stronger activity compared to CaMV35S promoter respectively. The correlation between GUS activity and uidA-mRNA levels in transgenic tobacco plants were identified by qRT-PCR. Both CaMV35S and MSgt-FSgt promoters caused gene silencing but the degree of silencing are less in the case of the MSgt-FSgt promoter compared to CaMV35S. Quantification of GUS activity in individual plant cells driven by the MSgt-FSgt and the CaMV35S promoter were estimated using confocal laser scanning microscopy and compared.

CONCLUSION AND SIGNIFICANCE

We propose strong recombinant promoter MSgt-FSgt, developed in this study, could be very useful for high-level constitutive expression of transgenes in a wide variety of plant cells.