Creation and validation of a widely applicable multiple gene transfer vector system for stable transformation in plant

Isolation and characterization of a novel seed-specific promoter from peanut (Arachis hypogaea L.)

Peanut, whose seeds are ideal bioreactors for the production of recombinant proteins and/or nutrient metabolites, is one of the most important crop species worldwide. As important molecular tools, seed-specific promoters (SSPs) can direct the expression of foreign proteins specifically in seeds to avoid constitutive expression that can damage plants. However, few SSPs have been identified from this species. In this study, we isolated a novel SSP (we named it AHSSP2) from peanut. Several cis-acting elements commonly found in SSPs, including 3 copies of RYREPEAT elements, were dispersed throughout the 1970-bp sequence of AHSSP2. The sequence was then substituted in place of the 35S promoter sequence in a pBI121 plasmid, which was subsequently transformed into Arabidopsis. Beta-glucuronidase (GUS) staining showed that AHSSP2 can drive GUS gene expression in the mature seeds of transgenic Arabidopsis, excluding within the testa. The cotyledons and hypocotyls of the germinating seeds of transgenic Arabidopsis seedlings also exhibited GUS activity, even after the seedlings became adult plants. No GUS activity was detected in nontransformed Arabidopsis at any stage. These results strongly suggested that AHSSP2 could drive the expression of foreign genes in a seed-specific manner. This study enriched SSP resources, and the results showed that AHSSP2 could be potentially utilized in peanut and other crop species to improve seed quality, such as modifications to seed oil content.

A highly pathogenic porcine reproductive and respiratory syndrome virus candidate vaccine based on Japanese encephalitis virus replicon system

In the swine industry, porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease which causes heavy economic losses worldwide. Effective prevention and disease control is an important issue. In this study, we described the construction of a Japanese encephalitis virus (JEV) DNA-based replicon with a cytomegalovirus (CMV) promoter based on the genome of Japanese encephalitis live vaccine virus SA14-14-2, which is capable of offering a potentially novel way to develop and produce vaccines against a major pathogen of global health. This JEV DNA-based replicon contains a large deletion in the structural genes (C-prM-E). A PRRSV GP5/M was inserted into the deletion position of JEV DNA-based replicons to develop a chimeric replicon vaccine candidate for PRRSV. The results showed that BALB/c mice models with the replicon vaccines pJEV-REP-G-2A-M-IRES and pJEV-REP-G-2A-M stimulated antibody responses and induced a cellular immune response. Analysis of ELSA data showed that vaccination with the replicon vaccine expressing GP5/M induced a better antibodies response than traditional DNA vaccines. Therefore, the results suggested that this ectopic expression system based on JEV DNA-based replicons may represent a useful molecular platform for various biological applications, and the JEV DNA-based replicons expressing GP5/M can be further developed into a novel, safe vaccine candidate for PRRS.

Development of an R4 dual-site (R4DS) gateway cloning system enabling the efficient simultaneous cloning of two desired sets of promoters and open reading frames in a binary vector for plant research

Vast numbers of proteins work cooperatively to exert their functions in various cells. In order to understand the functions and molecular mechanisms of these proteins in plants, analyses of transgenic plants that concomitantly express two protein-coding genes are often required. We developed a novel Gateway cloning technology-compatible binary vector system, the R4 dual-site (R4DS) Gateway cloning system, which enables the easy and efficient cloning of two desired sets of promoters and open reading frames (ORFs) into a binary vector using promoter and ORF entry clones. In this system, C-terminal fusions with 17 kinds of tags including visible reporters and epitope tags are available for each ORF, and selection by four kinds of resistance markers is possible. We verified that the R4DS Gateway cloning system functioned well in Arabidopsis thaliana by observing the expression and localization patterns of fluorescent proteins fused with organelle-targeting signals and driven by stomatal-lineage specific promoters. We also confirmed that the two cloning sites in the R4DS Gateway cloning system were equivalent and independently regulated. The results obtained indicate that the R4DS Gateway cloning system facilitates detailed comparisons of the expression patterns of two promoters as well as co-localization and interaction analyses of two proteins in specific cells in plants.

Co-overexpression of the Constitutively Active Form of OsbZIP46 and ABA-Activated Protein Kinase SAPK6 Improves Drought and Temperature Stress Resistance in Rice

Drought is one of the major abiotic stresses threatening rice (Oryza sativa) production worldwide. Drought resistance is controlled by multiple genes, and therefore, a multi-gene genetic engineering strategy is theoretically useful for improving drought resistance. However, the experimental evidence for such a strategy is still lacking. In this study, a few drought-responsive genes from rice were assembled by a multiple-round site-specific assembly system, and the constructs were introduced into the rice cultivar KY131 via Agrobacterium-mediated transformation. The transgenic lines of the multi-gene and corresponding single-gene constructs were pre-evaluated for drought resistance. We found that the co-overexpression of two genes, encoding a constitutively active form of a bZIP transcription factor (OsbZIP46CA1) and a protein kinase (SAPK6) involved in the abscisic acid signaling pathway, showed significantly enhanced drought resistance compared with the single-gene transgenic lines and the negative transgenic plants. Single-copy lines of this bi-gene combination (named XL22) and the corresponding single-gene lines were further evaluated for drought resistance in the field using agronomical traits. The results showed that XL22 exhibited greater yield, biomass, spikelet number, and grain number under moderate drought stress conditions. The seedling survival rate of XL22 and the single-gene overexpressors after drought stress treatment also supported the drought resistance results. Furthermore, expression profiling by RNA-Seq revealed that many genes involved in the stress response were specifically up-regulated in the drought-treated XL22 lines and some of the stress-related genes activated in CA1-OE and SAPK6-OE were distinct, which could partially explain the different performances of these lines with respect to drought resistance. In addition, the XL22 seedlings showed improved tolerance to heat and cold stresses. Our results demonstrate that the multi-gene assembly in an appropriate combination may be a promising approach in the genetic improvement of drought resistance.

Elevation of the Yields of Very Long Chain Polyunsaturated Fatty Acids via Minimal Codon Optimization of Two Key Biosynthetic Enzymes

Eicosapentaenoic acid (EPA, 20:5Δ^5,8,11,14,17) and Docosahexaenoic acid (DHA, 22:6Δ^{4,7,10,13,16,19}) are nutritionally beneficial to human health. Transgenic production of EPA and DHA in oilseed crops by transferring genes originating from lower eukaryotes, such as microalgae and fungi, has been attempted in recent years. However, the low yield of EPA and DHA produced in these transgenic crops is a major hurdle for the commercialization of these transgenics. Many factors can negatively affect transgene expression, leading to a low level of converted fatty acid products. Among these the codon bias between the transgene donor and the host crop is one of the major contributing factors. Therefore, we carried out codon optimization of a fatty acid delta-6 desaturase gene PinD6 from the fungus Phytophthora infestans, and a delta-9 elongase gene, IgASE1 from the microalga Isochrysis galbana for expression in Saccharomyces cerevisiae and Arabidopsis respectively. These are the two key genes encoding enzymes for driving the first catalytic steps in the Δ6 desaturation/Δ6 elongation and the Δ9 elongation/Δ8 desaturation pathways for EPA/DHA biosynthesis. Hence expression levels of these two genes are important in determining the final yield of EPA/DHA. Via PCR-based mutagenesis we optimized the least preferred codons within the first 16 codons at their N-termini, as well as the most biased CGC codons (coding for arginine) within the entire sequences of both genes. An expression study showed that transgenic Arabidopsis plants harbouring the codon-optimized IgASE1 contained 64% more elongated fatty acid products than plants expressing the native IgASE1 sequence, whilst Saccharomyces cerevisiae expressing the codon optimized PinD6 yielded 20 times more desaturated products than yeast expressing wild-type (WT) PinD6. Thus the codon optimization strategy we developed here offers a simple, effective and low-cost alternative to whole gene synthesis for high expression of foreign genes in yeast and Arabidopsis.

Simultaneous knockdown of six non-family genes using a single synthetic RNAi fragment in Arabidopsis thaliana

BACKGROUND

Genetic engineering of plants that results in successful establishment of new biochemical or regulatory pathways requires stable introduction of one or more genes into the plant genome. It might also be necessary to down-regulate or turn off expression of endogenous genes in order to reduce activity of competing pathways. An established way to knockdown gene expression in plants is expressing a hairpin-RNAi construct, eventually leading to degradation of a specifically targeted mRNA. Knockdown of multiple genes that do not share homologous sequences is still challenging and involves either sophisticated cloning strategies to create vectors with different serial expression constructs or multiple transformation events that is often restricted by a lack of available transformation markers.

RESULTS

Synthetic RNAi fragments were assembled in yeast carrying homologous sequences to six or seven non-family genes and introduced into pAGRIKOLA. Transformation of Arabidopsis thaliana and subsequent expression analysis of targeted genes proved efficient knockdown of all target genes.

CONCLUSIONS

We present a simple and cost-effective method to create constructs to simultaneously knockdown multiple non-family genes or genes that do not share sequence homology. The presented method can be applied in plant and animal synthetic biology as well as traditional plant and animal genetic engineering.