Minimizing the unpredictability of transgene expression in plants: the role of genetic insulators

Small DNA elements that act as both insulators and silencers in plants

Insulators are cis-regulatory elements that separate transcriptional units, whereas silencers are elements that repress transcription regardless of their position. In plants, these elements remain largely uncharacterized. Here, we use the massively parallel reporter assay Plant STARR-seq with short fragments of eight large insulators to identify more than 100 fragments that block enhancer activity. The short fragments can be combined to generate more powerful insulators that abolish the capacity of the strong viral 35S enhancer to activate the 35S minimal promoter. Unexpectedly, when tested upstream of weak enhancers, these fragments act as silencers and repress transcription. Thus, these elements are capable of both insulating or repressing transcription dependent upon regulatory context. We validate our findings in stable transgenic Arabidopsis, maize, and rice plants. The short elements identified here should be useful building blocks for plant biotechnology efforts.

Mining the Utricularia gibba genome for insulator-like elements for genetic engineering

Introduction

Gene expression is often controlled via cis-regulatory elements (CREs) that modulate the production of transcripts. For multi-gene genetic engineering and synthetic biology, precise control of transcription is crucial, both to insulate the transgenes from unwanted native regulation and to prevent readthrough or cross-regulation of transgenes within a multi-gene cassette. To prevent this activity, insulator-like elements, more properly referred to as transcriptional blockers, could be inserted to separate the transgenes so that they are independently regulated. However, only a few validated insulator-like elements are available for plants, and they tend to be larger than ideal.

Methods

To identify additional potential insulator-like sequences, we conducted a genome-wide analysis of Utricularia gibba (humped bladderwort), one of the smallest known plant genomes, with genes that are naturally close together. The 10 best insulator-like candidates were evaluated in vivo for insulator-like activity.

Results

We identified a total of 4,656 intergenic regions with expression profiles suggesting insulator-like activity. Comparisons of these regions across 45 other plant species (representing Monocots, Asterids, and Rosids) show low levels of syntenic conservation of these regions. Genome-wide analysis of unmethylated regions (UMRs) indicates ~87% of the targeted regions are unmethylated; however, interpretation of this is complicated because U. gibba has remarkably low levels of methylation across the genome, so that large UMRs frequently extend over multiple genes and intergenic spaces. We also could not identify any conserved motifs among our selected intergenic regions or shared with existing insulator-like elements for plants. Despite this lack of conservation, however, testing of 10 selected intergenic regions for insulator-like activity found two elements on par with a previously published element (EXOB) while being significantly smaller.

Discussion

Given the small number of insulator-like elements currently available for plants, our results make a significant addition to available tools. The high hit rate (2 out of 10) also implies that more useful sequences are likely present in our selected intergenic regions; additional validation work will be required to identify which will be most useful for plant genetic engineering.

Frontiers and techniques in plant gene regulation

Understanding plant gene regulation has been a priority for generations of plant scientists. However, due to its complex nature, the regulatory code governing plant gene expression has yet to be deciphered comprehensively. Recently developed methods-often relying on next-generation sequencing technology and state-of-the-art computational approaches-have started to further our understanding of the gene regulatory logic used by plants. In this review, we discuss these methods and the insights into the regulatory code of plants that they can yield.

Integrated approach for the molecular characterization of edited plants obtained via Agrobacterium tumefaciens-mediated gene transfer

Agrobacterium tumefaciens-mediated gene transfer—actually the most used method to engineer plants—may lead to integration of multiple copies of T-DNA in the plant genome, as well as to chimeric tissues composed of modified cells and wild type cells. A molecular characterization of the transformed lines is thus a good practice to select the best ones for further investigation. Nowadays, several quantitative and semi-quantitative techniques are available to estimate the copy number (CN) of the T-DNA in genetically modified plants. In this study, we compared three methods based on (1) real-time polymerase chain reaction (qPCR), (2) droplet digital PCR (ddPCR), and (3) next generation sequencing (NGS), to carry out a molecular characterization of grapevine edited lines. These lines contain a knock-out mutation, obtained via CRISPR/Cas9 technology, in genes involved in plant susceptibility to two important mildew diseases of grapevine. According to our results, qPCR and ddPCR outputs are largely in agreement in terms of accuracy, especially for low CN values, while ddPCR resulted more precise than qPCR. With regard to the NGS analysis, the CNs detected with this method were often not consistent with those calculated by qPCR and ddPCR, and NGS was not able to discriminate the integration points in three out of ten lines. Nevertheless, the NGS method can positively identify T-DNA truncations or the presence of tandem/inverted repeats, providing distinct and relevant information about the transgene integration asset. Moreover, the expression analysis of Cas9 and single guide RNA (sgRNA), and the sequencing of the target site added new information to be related to CN data. This work, by reporting a practical case-study on grapevine edited lines, explores pros and cons of the most advanced diagnostic techniques available for the precocious selection of the proper transgenic material. The results may be of interest both to scientists developing new transgenic lines, and to laboratories in charge of GMO control.

Insulators in Plants: Progress and Open Questions

The genomes of higher eukaryotes are partitioned into topologically associated domains or TADs, and insulators (also known as boundary elements) are the key elements responsible for their formation and maintenance. Insulators were first identified and extensively studied in Drosophila as well as mammalian genomes, and have also been described in yeast and plants. In addition, many insulator proteins are known in Drosophila, and some have been investigated in mammals. However, much less is known about this important class of non-coding DNA elements in plant genomes. In this review, we take a detailed look at known plant insulators across different species and provide an overview of potential determinants of plant insulator functions, including cis-elements and boundary proteins. We also discuss methods previously used in attempts to identify plant insulators, provide a perspective on their importance for research and biotechnology, and discuss areas of potential future research.

Perspective: 50 years of plant chromosome biology

The past 50 years has been the greatest era of plant science discovery, and most of the discoveries have emerged from or been facilitated by our knowledge of plant chromosomes. At last we have descriptive and mechanistic outlines of the information in chromosomes that programs plant life. We had almost no such information 50 years ago when few had isolated DNA from any plant species. The important features of genes have been revealed through whole genome comparative genomics and testing of variants using transgenesis. Progress has been enabled by the development of technologies that had to be invented and then become widely available. Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) have played extraordinary roles as model species. Unexpected evolutionary dramas were uncovered when learning that chromosomes have to manage constantly the vast numbers of potentially mutagenic families of transposons and other repeated sequences. The chromatin-based transcriptional and epigenetic mechanisms that co-evolved to manage the evolutionary drama as well as gene expression and 3-D nuclear architecture have been elucidated these past 20 years. This perspective traces some of the major developments with which I have become particularly familiar while seeking ways to improve crop plants. I draw some conclusions from this look-back over 50 years during which the scientific community has (i) exposed how chromosomes guard, readout, control, recombine, and transmit information that programs plant species, large and small, weed and crop, and (ii) modified the information in chromosomes for the purposes of genetic, physiological, and developmental analyses and plant improvement.

IbERF71, with IbMYB340 and IbbHLH2, coregulates anthocyanin accumulation by binding to the IbANS1 promoter in purple-fleshed sweet potato (Ipomoea batatas L.)

KEY MESSAGE

The transcription factor (TF) IbERF71 forms a novel complex, IbERF71-IbMYB340-IbbHLH2, to coregulate anthocyanin biosynthesis by binding to the IbANS1 promoter in purple-fleshed sweet potatoes. Purple-fleshed sweet potato (Ipomoea batatas L.) is very popular because of its abundant anthocyanins, which are natural pigments with multiple physiological functions. TFs involved in regulating anthocyanin biosynthesis have been identified in many plants. However, the molecular mechanism of anthocyanin biosynthesis in purple-fleshed sweet potatoes has rarely been examined. In this study, TF IbERF71 and its partners were screened by bioinformatics and RT-qPCR analysis. The results showed that the expression levels of IbERF71 and partners IbMYB340 and IbbHLH2 were higher in purple-fleshed sweet potatoes than in other colors and that the expression levels positively correlated with anthocyanin contents. Moreover, transient expression assays showed that cotransformation of IbMYB340+IbbHLH2 resulted in anthocyanin accumulation in tobacco leaves and strawberry receptacles, and additional IbERF71 significantly increased visual aspects. Furthermore, the combination of the three TFs significantly increased the expression levels of FvANS and FvGST, which are involved in anthocyanin biosynthesis and transport of strawberry receptacles. The dual-luciferase reporter system verified that cotransformation of the three TFs enhanced the transcription activity of IbANS1. In addition, yeast two-hybrid and firefly luciferase complementation assays revealed that IbMYB340 interacted with IbbHLH2 and IbERF71 but IbERF71 could not interact with IbbHLH2 in vitro. In summary, our findings provide novel evidence that IbERF71 and IbMYB340-IbbHLH2 form the regulatory complex IbERF71-IbMYB340-IbbHLH2 that coregulates anthocyanin accumulation by binding to the IbANS1 promoter in purple-fleshed sweet potatoes. Thus, the present study provides a new regulatory network of anthocyanin biosynthesis and strong insight into the color development of purple-fleshed sweet potatoes.

Quantitative and Predictive Genetic Parts for Plant Synthetic Biology

Plant synthetic biology aims to harness the natural abilities of plants and to turn them to new purposes. A primary goal of plant synthetic biology is to produce predictable and programmable genetic circuits from simple regulatory elements and well-characterized genetic components. The number of available DNA parts for plants is increasing, and the methods for rapid quantitative characterization are being developed, but the field of plant synthetic biology is still in its early stages. We here describe methods used to describe the quantitative properties of genetic components needed for plant synthetic biology. Once the quantitative properties and transfer function of a variety of genetic parts are known, computers can select the optimal components to assemble into functional devices, such as toggle switches and positive feedback circuits. However, while the variety of circuits and traits that can be put into plants are limitless, doing synthetic biology in plants poses unique challenges. Plants are composed of differentiated cells and tissues, each representing potentially unique regulatory or developmental contexts to introduced synthetic genetic circuits. Further, plants have evolved to be highly sensitive to environmental influences, such as light or temperature, any of which can affect the quantitative function of individual parts or whole circuits. Measuring the function of plant components within the context of a plant cell and, ideally, in a living plant, will be essential to using these components in gene circuits with predictable function. Mathematical modeling will be needed to account for the variety of contexts a genetic part will experience in different plant tissues or environments. With such understanding in hand, it may be possible to redesign plant traits to serve human and environmental needs.

Towards oilcane: Engineering hyperaccumulation of triacylglycerol into sugarcane stems

Metabolic engineering to divert carbon flux from sucrose to oil in high biomass crop like sugarcane is an emerging strategy to boost lipid yields per hectare for biodiesel production. Sugarcane stems comprise more than 70% of the crops' biomass and can accumulate sucrose in excess of 20% of their extracted juice. The energy content of oils in the form of triacylglycerol (TAG) is more than twofold that of carbohydrates. Here, we report a step change in TAG accumulation in sugarcane stem tissues achieving an average of 4.3% of their dry weight (DW) in replicated greenhouse experiments by multigene engineering. The metabolic engineering included constitutive co‐expression of wrinkled1; diacylglycerol acyltransferase1‐2; cysteine‐oleosin; and ribonucleic acid interference‐suppression of sugar‐dependent1. The TAG content in leaf tissue was also elevated by more than 400‐fold compared to non‐engineered sugarcane to an average of 8.0% of the DW and the amount of total fatty acids reached about 13% of the DW. With increasing TAG accumulation an increase of 18:1 unsaturated fatty acids was observed at the expense of 16:0 and 18:0 saturated fatty acids. Total biomass accumulation, soluble lignin, Brix and juice content were significantly reduced in the TAG hyperaccumulating sugarcane lines. Overcoming this yield drag by engineering lipid accumulation into late stem development will be critical to exceed lipid yields of current oilseed crops.

The M4 insulator, the TM2 matrix attachment region, and the double copy of the heavy chain gene contribute to the enhanced accumulation of the PHB-01 antibody in tobacco plants

The expression of recombinant proteins in plants is a valuable alternative to bioreactors using mammalian cell systems. Ease of scaling, and their inability to host human pathogens, enhance the use of plants to generate complex therapeutic products such as monoclonal antibodies. However, stably transformed plants expressing antibodies normally have a poor accumulation of these proteins that probably arise from the negative positional effects of their flanking chromatin. The induction of boundaries between the transgenes and the surrounding DNA using matrix attachment regions (MAR) and insulator elements may minimize these effects. With the PHB-01 antibody as a model, we demonstrated that the insertion of DNA elements, the TM2 (MAR) and M4 insulator, flanking the transcriptional cassettes that encode the light and heavy chains of the PHB-01 antibody, increased the protein accumulation that remained stable in the first plant progeny. The M4 insulator had a stronger effect than the TM2, with over a twofold increase compared to the standard construction. This effect was probably associated with an enhancer-promoter interference. Moreover, transgenic plants harboring two transcriptional units encoding for the PHB-01 heavy chain combined with both TM2 and M4 elements enhanced the accumulation of the antibody. In summary, the M4 combined with a double transcriptional unit of the heavy chain may be a suitable strategy for potentiating PHB-01 production in tobacco plants.

Generation of a selectable marker free, highly expressed single copy locus as landing pad for transgene stacking in sugarcane

A selectable marker free, highly expressed single copy locus flanked by insulators was created as landing pad for transgene stacking in sugarcane. These events displayed superior transgene expression compared to single-copy transgenic lines lacking insulators. Excision of the selectable marker gene from transgenic sugarcane lines was supported by FLPe/FRT site-specific recombination. Sugarcane, a tropical C4 grass in the genus Saccharum (Poaceae), accounts for nearly 80% of sugar produced worldwide and is also an important feedstock for biofuel production. Generating transgenic sugarcane with predictable and stable transgene expression is critical for crop improvement. In this study, we generated a highly expressed single copy locus as landing pad for transgene stacking. Transgenic sugarcane lines with stable integration of a single copy nptII expression cassette flanked by insulators supported higher transgene expression along with reduced line to line variation when compared to single copy events without insulators by NPTII ELISA analysis. Subsequently, the nptII selectable marker gene was efficiently excised from the sugarcane genome by the FLPe/FRT site-specific recombination system to create selectable marker free plants. This study provides valuable resources for future gene stacking using site-specific recombination or genome editing tools.

The Rapid Methylation of T-DNAs Upon Agrobacterium Inoculation in Plant Leaves

Agrobacterium tumefaciens has been foundational in the development of transgenic plants for both agricultural biotechnology and plant molecular research. However, the transformation efficiency and level of transgene expression obtained for any given construct can be highly variable. These inefficiencies often require screening of many lines to find one with consistent and heritable transgene expression. Transcriptional gene silencing is known to affect transgene expression, and is associated with DNA methylation, especially of cytosines in symmetric CG and CHG contexts. While the specificity, heritability and silencing-associated effects of DNA methylation of transgene sequences have been analyzed in many stably transformed plants, the methylation status of transgene sequences in the T-DNA during the transformation process has not been well-studied. Here we used agro-infiltration of the eGFP reporter gene in Nicotiana benthamiana leaves driven by either an AtEF1α-A4 or a CaMV-35S promoter to study early T-DNA methylation patterns of these promoter sequences. The T-DNA was examined by amplicon sequencing following sodium bisulfite treatment using three different sequencing platforms: Sanger sequencing, Ion Torrent PGM, and the Illumina MiSeq. Rapid DNA methylation was detectable in each promoter region just 2-3 days post-infiltration and the levels continued to rapidly accumulate over the first week, then steadily up to 21 days later. Cytosines in an asymmetric context (CHH) were the most heavily and rapidly methylated. This suggests that early T-DNA methylation may be important in determining the epigenetic and transcriptional fate of integrated transgenes. The Illumina MiSeq platform was the most sensitive and robust way of detecting and following the methylation profiles of the T-DNA promoters. The utility of the methods was then used to show a subtle but significant difference in promoter methylation during intron-mediated enhancement. In addition, the method was able to detect an increase in promoter methylation when the eGFP reporter gene was targeted by siRNAs generated by co-infiltration of a hairpin RNAi construct.

Arabidopsis UMAMIT24 and 25 are amino acid exporters involved in seed loading

Phloem-derived amino acids are the major source of nitrogen supplied to developing seeds. Amino acid transfer from the maternal to the filial tissue requires at least one cellular export step from the maternal tissue prior to the import into the symplasmically isolated embryo. Some members of UMAMIT (usually multiple acids move in an out transporter) family (UMAMIT11, 14, 18, 28, and 29) have previously been implicated in this process. Here we show that additional members of the UMAMIT family, UMAMIT24 and UMAMIT25, also function in amino acid transfer in developing seeds. Using a recently published yeast-based assay allowing detection of amino acid secretion, we showed that UMAMIT24 and UMAMIT25 promote export of a broad range of amino acids in yeast. In plants, UMAMIT24 and UMAMIT25 are expressed in distinct tissues within developing seeds; UMAMIT24 is mainly expressed in the chalazal seed coat and localized on the tonoplast, whereas the plasma membrane-localized UMAMIT25 is expressed in endosperm cells. Seed amino acid contents of umamit24 and umamit25 knockout lines were both decreased during embryogenesis compared with the wild type, but recovered in the mature seeds without any deleterious effect on yield. The results suggest that UMAMIT24 and 25 play different roles in amino acid translocation from the maternal to filial tissue; UMAMIT24 could have a role in temporary storage of amino acids in the chalaza, while UMAMIT25 would mediate amino acid export from the endosperm, the last step before amino acids are taken up by the developing embryo.

Engineering synthetic regulatory circuits in plants

Plant synthetic biology is a rapidly emerging field that aims to engineer genetic circuits to function in plants with the same reliability and precision as electronic circuits. These circuits can be used to program predictable plant behavior, producing novel traits to improve crop plant productivity, enable biosensors, and serve as platforms to synthesize chemicals and complex biomolecules. Herein we introduce the importance of developing orthogonal plant parts and the need for quantitative part characterization for mathematical modeling of complex circuits. In particular, transfer functions are important when designing electronic-like genetic controls such as toggle switches, positive/negative feedback loops, and Boolean logic gates. We then discuss potential constraints and challenges in synthetic regulatory circuit design and integration when using plants. Finally, we highlight current and potential plant synthetic regulatory circuit applications.

A Brief History of Promoter Development for Use in Transgenic Maize Applications

Promoters regulate gene expression, and are essential biotechnology tools. Since its introduction in the mid-1990s, biotechnology has greatly enhanced maize productivity primarily through the development of insect control and herbicide tolerance traits. Additional biotechnology applications include improving seed nutrient composition, industrial protein production, therapeutic production, disease resistance, abiotic stress resistance, and yield enhancement. Biotechnology has also greatly expanded basic research into important mechanisms that govern plant growth and reproduction. Many novel promoters have been developed to facilitate this work, but only a few are widely used. Transgene optimization includes a variety of strategies some of which effect promoter structure. Recent reviews examine the state of the art with respect to transgene design for biotechnology applications. This chapter examines the use of transgene technology in maize, focusing on the way promoters are selected and used. The impact of new developments in genomic technology on promoter structure is also discussed.

Towards the development of a sustainable soya bean-based feedstock for aquaculture

Soya bean (Glycine max (L.) Merr.) is sought after for both its oil and protein components. Genetic approaches to add value to either component are ongoing efforts in soya bean breeding and molecular biology programmes. The former is the primary vegetable oil consumed in the world. Hence, its primary usage is in direct human consumption. As a means to increase its utility in feed applications, thereby expanding the market of soya bean coproducts, we investigated the simultaneous displacement of marine ingredients in aquafeeds with soya bean-based protein and a high Omega-3 fatty acid soya bean oil, enriched with alpha-linolenic and stearidonic acids, in both steelhead trout (Oncorhynchus mykiss) and Kampachi (Seriola rivoliana). Communicated herein are aquafeed formulations with major reduction in marine ingredients that translates to more total Omega-3 fatty acids in harvested flesh. Building off of these findings, subsequent efforts were directed towards a genetic strategy that would translate to a prototype design of an optimal identity-preserved soya bean-based feedstock for aquaculture, whereby a multigene stack approach for the targeted synthesis of two value-added output traits, eicosapentaenoic acid and the ketocarotenoid, astaxanthin, were introduced into the crop. To this end, the systematic introduction of seven transgenic cassettes into soya bean, and the molecular and phenotypic evaluation of the derived novel events are described.

Multiple Patterns of Regulation and Overexpression of a Ribonuclease-Like Pathogenesis-Related Protein Gene, OsPR10a, Conferring Disease Resistance in Rice and Arabidopsis

An abundant 17 kDa RNase, encoded by OsPR10a (also known as PBZ1), was purified from P_i-starved rice suspension-cultured cells. Biochemical analysis showed that the range of optimal temperature for its RNase activity was 40–70°C and the optimum pH was 5.0. Disulfide bond formation and divalent metal ion Mg²⁺ were required for the RNase activity. The expression of OsPR10a::GUS in transgenic rice was induced upon phosphate (P_i) starvation, wounding, infection by the pathogen Xanthomonas oryzae pv. oryzae (Xoo), leaf senescence, anther, style, the style-ovary junction, germinating embryo and shoot. We also provide first evidence in whole-plant system, demonstrated that OsPR10a-overexpressing in rice and Arabidopsis conferred significant level of enhanced resistance to infection by the pathogen Xoo and Xanthomona campestris pv. campestris (Xcc), respectively. Transgenic rice and Arabidopsis overexpressing OsPR10a significantly increased the length of primary root under phosphate deficiency (-P_i) condition. These results showed that OsPR10a might play multiple roles in phosphate recycling in phosphate-starved cells and senescing leaves, and could improve resistance to pathogen infection and/or against chewing insect pests. It is possible that P_i acquisition or homeostasis is associated with plant disease resistance. Our findings suggest that gene regulation of OsPR10a could act as a good model system to unravel the mechanisms behind the correlation between P_i starvation and plant-pathogen interactions, and also provides a potential application in crops disease resistance.

Genetic Screening for Arabidopsis Mutants Defective in STA1 Regulation under Thermal Stress Implicates the Existence of Regulators of Its Specific Expression, and the Genetic Interactions in the Stress Signaling Pathways

To cope with environmental stresses, plants have developed various stress tolerance mechanisms that involve the induction of many stress responsive genes through stress-specific and common signaling pathways. Stress-specific/common transcription factors, rather than general basal factors, were considered important in this stress tolerance. The Arabidopsis STABILIZED1 (STA1) gene encodes a putative pre-mRNA splicing factor that is similar to the human U5 snRNP-associated 102-kDa protein and the yeast pre-mRNA splicing factors, PRP1p and Prp6p. As pre-mRNA splicing is a necessary process for proper gene expression in eukaryotes, STA1 is expected to be constantly functional in all conditions. Interestingly, STA1 expression is induced by temperature stresses, and STA1 recessive mutation (sta1-1) resulted in temperature stress-specific hypersensitivity. This suggests STA1's stress specific function in addition to its presumed "housekeeping" role. In order to establish the genetic system to understand the regulation of STA1 expression in temperature stresses, we generated a bioluminescent Arabidopsis plant harboring the STA1 promoter fused to the firefly luciferase coding sequence (STA1p-LUC). Through genetic analysis, the bioluminescent Arabidopsis homozygous for one-copy STA1p-LUC was isolated and characterized. In this STA1p-LUC line, the expression patterns of STA1p-LUC were similar to those of the endogenous STA1 gene under cold and heat stresses. The STA1p-LUC line was then chemically mutagenized and screened to isolate the genetic loci of STA1 regulators under cold or heat stresses. Mutants with altered STA1p-LUC luminescence were identified and further confirmed through luminescence imaging in the next generation and analysis of endogenous STA1 expression. The categorization of STA1p-LUC deregulated mutants implicated the existence of cold or heat stress-specific as well as common genetic regulators for STA1 expression. Interestingly, some mutants showed opposite-directional deregulation of STA1 expression depending on the type of thermal stress, suggesting that the loci may represent important switch factors which determine the direction of signaling pathways for STA1 expression in response to temperature.

A chimeric cry8Ea1 gene flanked by MARs efficiently controls Holotrichia parallela

Peanuts transformed with the synthetic cry8Ea1 gene flanked by MARs are a potentially effective control strategy against white grubs. Cry8Ea1 protein levels of the construct containing MARs were increased by 2.5 times. White grubs are now recognized as the most important pests of peanut worldwide. A synthetic cry8Ea1 gene, which was toxic to Holotrichia parallela larvae, was expressed in chimeric peanut roots using an Agrobacterium rhizogenes-mediated transformation system. The relative mRNA and protein levels of the cry8Ea1 gene were confirmed by quantitative real-time PCR and ELISA, respectively. The effects of matrix attachment regions (MARs) on the expression and activity of the cry8Ea1 gene were analyzed. The average expression level of cry8Ea1 in peanut roots was higher for the plants harboring constructs flanked by MARs from tobacco. Moreover, differing from previous studies, the synthetic cry8Ea1 gene flanked by MARs showed more variation in protein levels than mRNA levels. These composite plants containing cry8Ea1 gene flanked by MARs exhibited a high toxicity against Holotrichia parallela larvae as shown by bioassay analysis, thus offering a potential effective combination to control subterranean insects in peanuts.

Screening promoters for Anthurium transformation using transient expression

KEY MESSAGE : There are multiple publications on Anthurium transformation, yet a commercial product has not been achieved. This may be due to use of non-optimum promoters here we address this problem. Different promoters and tissue types were evaluated for transient β-glucuronidase (GUS) expression in Anthurium andraeanum Hort. 'Marian Seefurth' following microprojectile bombardment. Plasmids containing the Ubiquitin 2, Actin 1, Cytochrome C1 from rice, Ubiquitin 1 from maize and 35S promoter from Cauliflower Mosaic Virus fused to a GUS reporter gene were bombarded into in vitro grown anthurium lamina, somatic embryos and roots. The number of GUS foci and the intensity of GUS expression were evaluated for each construct. Ubiquitin promoters from rice and maize resulted in the highest number of expressing cells in all tissues examined. Due to the slow growth of anthurium plants, development of transgenic anthurium plants takes years. This research has rapidly identified multiple promoters that express in various anthurium tissues facilitating the development of transformation vectors for the expression of desirable traits in anthurium plants.

Learning from nature: new approaches to the metabolic engineering of plant defense pathways

Biotechnological manipulation of plant defense pathways can increase crop resistance to herbivores and pathogens while also increasing yields of medicinal, industrial, flavor and fragrance compounds. The most successful achievements in engineering defense pathways can be attributed to researchers striving to imitate natural plant regulatory mechanisms. For example, the introduction of transcription factors that control several genes in one pathway is often a valuable strategy to increase flux in that pathway. The use of multi-gene cassettes which mimic natural gene clusters can facilitate coordinated regulation of a pathway and speed transformation efforts. The targeting of defense pathway genes to organs and tissues in which the defensive products are typically made and stored can also increase yield as well as defensive potential.