Agrobacterium-mediated transformation of Solanum tuberosum L. cv. 'Russet Burbank'

Eukaryotic splicing machinery in the plant-virus battleground

Plant virual infections are mainly caused by plant-virus parasitism which affects ecological communities. Some viruses are highly pathogen specific that can infect only specific plants, while some can cause widespread harm, such as tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV). After a virus infects the host, undergoes a series of harmful effects, including the destruction of host cell membrane receptors, changes in cell membrane components, cell fusion, and the production of neoantigens on the cell surface. Therefore, competition between the host and the virus arises. The virus starts gaining control of critical cellular functions of the host cells and ultimately affects the fate of the targeted host plants. Among these critical cellular processes, alternative splicing (AS) is an essential posttranscriptional regulation process in RNA maturation, which amplify host protein diversity and manipulates transcript abundance in response to plant pathogens. AS is widespread in nearly all human genes and critical in regulating animal-virus interactions. In particular, an animal virus can hijack the host splicing machinery to re-organize its compartments for propagation. Changes in AS are known to cause human disease, and various AS events have been reported to regulate tissue specificity, development, tumour proliferation, and multi-functionality. However, the mechanisms underlying plant-virus interactions are poorly understood. Here, we summarize the current understanding of how viruses interact with their plant hosts compared with humans, analyze currently used and putative candidate agrochemicals to treat plant-viral infections, and finally discussed the potential research hotspots in the future. This article is categorized under: RNA Processing > Splicing Mechanisms RNA Processing > Splicing Regulation/Alternative Splicing.

State of the Art of Genetic Engineering in Potato: From the First Report to Its Future Potential

Potato (Solanum tuberosum L.) is a crop of world importance that produces tubers of high nutritional quality. It is considered one of the promising crops to overcome the challenges of poverty and hunger worldwide. However, it is exposed to different biotic and abiotic stresses that can cause significant losses in production. Thus, potato is a candidate of special relevance for improvements through conventional breeding and biotechnology. Since conventional breeding is time-consuming and challenging, genetic engineering provides the opportunity to introduce/switch-off genes of interest without altering the allelic combination that characterize successful commercial cultivars or to induce targeted sequence modifications by New Breeding Techniques. There is a variety of methods for potato improvement via genetic transformation. Most of them incorporate genes of interest into the nuclear genome; nevertheless, the development of plastid transformation protocols broadened the available approaches for potato breeding. Although all methods have their advantages and disadvantages, Agrobacterium-mediated transformation is the most used approach. Alternative methods such as particle bombardment, protoplast transfection with polyethylene glycol and microinjection are also effective. Independently of the DNA delivery approach, critical steps for a successful transformation are a rapid and efficient regeneration protocol and a selection system. Several critical factors affect the transformation efficiency: vector type, insert size, Agrobacterium strain, explant type, composition of the subculture media, selective agent, among others. Moreover, transient or stable transformation, constitutive or inducible promoters, antibiotic/herbicide resistance or marker-free strategies can be considered. Although great efforts have been made to optimize all the parameters, potato transformation protocols are highly genotype-dependent. Genome editing technologies provide promising tools in genetic engineering allowing precise modification of targeted sequences. Interestingly, transient expression of genome editing components in potato protoplasts was reported to generate edited plants without the integration of any foreign DNA, which is a valuable aspect from both a scientific and a regulatory perspective. In this review, current challenges and opportunities concerning potato genetic engineering strategies developed to date are discussed. We describe their critical parameters and constrains, and the potential application of the available tools for functional analyses or biotechnological purposes. Public concerns and safety issues are also addressed.

Development and Adoption of Genetically Engineered Plants for Virus Resistance: Advances, Opportunities and Challenges

Plant viruses cause yield losses to crops of agronomic and economic significance and are a challenge to the achievement of global food security. Although conventional plant breeding has played an important role in managing plant viral diseases, it will unlikely meet the challenges posed by the frequent emergence of novel and more virulent viral species or viral strains. Hence there is an urgent need to seek alternative strategies of virus control that can be more readily deployed to contain viral diseases. The discovery in the late 1980s that viral genes can be introduced into plants to engineer resistance to the cognate virus provided a new avenue for virus disease control. Subsequent advances in genomics and biotechnology have led to the refinement and expansion of genetic engineering (GE) strategies in crop improvement. Importantly, many of the drawbacks of conventional breeding, such as long lead times, inability or difficulty to cross fertilize, loss of desirable plant traits, are overcome by GE. Unfortunately, public skepticism towards genetically modified (GM) crops and other factors have dampened the early promise of GE efforts. These concerns are principally about the possible negative effects of transgenes to humans and animals, as well as to the environment. However, with regards to engineering for virus resistance, these risks are overstated given that most virus resistance engineering strategies involve transfer of viral genes or genomic segments to plants. These viral genomes are found in infected plant cells and have not been associated with any adverse effects in humans or animals. Thus, integrating antiviral genes of virus origin into plant genomes is hardly unnatural as suggested by GM crop skeptics. Moreover, advances in deep sequencing have resulted in the sequencing of large numbers of plant genomes and the revelation of widespread endogenization of viral genomes into plant genomes. This has raised the possibility that viral genome endogenization is part of an antiviral defense mechanism deployed by the plant during its evolutionary past. Thus, GM crops engineered for viral resistance would likely be acceptable to the public if regulatory policies were product-based (the North America regulatory model), as opposed to process-based. This review discusses some of the benefits to be gained from adopting GE for virus resistance, as well as the challenges that must be overcome to leverage this technology. Furthermore, regulatory policies impacting virus-resistant GM crops and some success cases of virus-resistant GM crops approved so far for cultivation are discussed.

Development of selectable marker-free transgenic potato plants expressing cry3A against the Colorado potato beetle (Leptinotarsa decemlineata Say)

BACKGROUND

Elimination of selectable marker genes (SMGs) is important for the safe assessment and commercial use of transgenic plants. The destructive and invasive Colorado potato beetle (CPB) poses a serious threat to potato production. In response to this need, selectable marker-free transgenic potato lines expressing cry3A were developed to control the damage and spread of CPB.

RESULTS

We simultaneously introduced cry3A and npt II genes harboured in different plasmids into the potato genome using the Agrobacterium-mediated cotransformation method. Four selectable marker-free transgenic potato (CT) lines expressing cry3A were developed by self-crossing segregation and molecular analyses, including Southern blot, western blot and enzyme-linked immunosorbent assay (ELISA) assays. CT lines were used in a resistance bioassay against CPB in the laboratory and field. In the laboratory, CT lines exhibited high resistance to CPB, and 100% mortality of first-instar larvae occurred 6 days after infestation. In the field, untransformed plant leaves were almost entirely consumed, with an average of 155 larvae present per plant 25 days after inoculation. However, CT lines showed no damage symptoms, with approximately 2.5 larvae surviving per plant.

CONCLUSION

We successfully eliminated SMGs from the transgenic potato lines expressing cry3A in order to decrease CPB damage, control the spread of this pest eastwards and alleviate the concern regarding the safe assessment of regulatory requirements. © 2015 Society of Chemical Industry.

Applications of biotechnology and genomics in potato improvement

Potato is the third most important global food crop and the most widely grown noncereal crop. As a species highly amenable to cell culture, it has a long history of biotechnology applications for crop improvement. This review begins with a historical perspective on potato improvement using biotechnology encompassing pathogen elimination, wide hybridization, ploidy manipulation and applications of cell culture. We describe the past developments and new approaches for gene transfer to potato. Transformation is highly effective for adding single genes to existing elite potato clones with no, or minimal, disturbances to their genetic background and represents the only effective way to produce isogenic lines of specific genotypes/cultivars. This is virtually impossible via traditional breeding as, due to the high heterozygosity in the tetraploid potato genome, the genetic integrity of potato clones is lost upon sexual reproduction as a result of allele segregation. These genetic attributes have also provided challenges for the development of genetic maps and applications of molecular markers and genomics in potato breeding. Various molecular approaches used to characterize loci, (candidate) genes and alleles in potato, and associating phenotype with genotype are also described. The recent determination of the potato genome sequence has presented new opportunities for genomewide assays to provide tools for gene discovery and enabling the development of robustly unique marker haplotypes spanning QTL regions. The latter will be useful in introgression breeding and whole-genome approaches such as genomic selection to improve the efficiency of selecting elite clones and enhancing genetic gain over time.

Evaluation of the resistance of transgenic potato plants expressing various levels of Cry3A against the Colorado potato beetle (Leptinotarsa decemlineata Say) in the laboratory and field

BACKGROUND

The Colorado potato beetle (CPB), Leptinotarsa decemlineata Say, is a destructive pest. The CPB is a quarantine pest in China, but has now invaded the Xinjiang Uygur Autonomous Region and is continuing to spread eastwards. To control the damage and overspreading, transgenic potato plants expressing Cry3A toxin were developed, and their resistance to CPB was evaluated by bioassays in the laboratory and field in 2009, 2010 and 2011.

RESULTS

The insect resistance of the high-dose (HD) transgenic lines was significantly greater than the middle-dose (MD) and low-dose (LD) transgenic lines regarding leaf consumption, biomass accumulation and mortality. The HD and MD transgenic lines showed 100% mortality when inoculated with first- and second-instar larvae; however, the LD transgenic lines showed about 50% mortality. The HD transgenic lines exhibited a significantly higher yield than the MD and LD transgenic lines owing to their high CPB resistance.

CONCLUSION

Commercially available transgenic potato plants with above 0.1% Cry3A of total soluble protein and NT control refugia could control damage, delay adaptation and halt dispersion eastwards. The two HD transgenic lines developed in this study, PAH1 and PAH2, are ideal for use as cultivars or germplasm to breed new cultivars.

Overexpression of 2-cysteine peroxiredoxin enhances tolerance to methyl viologen-mediated oxidative stress and high temperature in potato plants

Oxidative stress is one of the major causative factors for injury to plants exposed to environmental stresses. Plants have developed diverse defense mechanisms for scavenging oxidative stress-inducing molecules. The antioxidative enzyme 2-cysteine peroxiredoxin (2-Cys Prx) removes peroxides and protects the photosynthetic membrane from oxidative damage. In this study, transgenic potato (Solanum tuberosum L. cv. Atlantic) expressing At2-Cys Prx under control of the oxidative stress-inducible SWPA2 promoter or enhanced CaMV 35S promoter (referred to as SP and EP plants, respectively) was generated using Agrobacterium-mediated transformation. The transgenic plants were tested for tolerance to stress. Following treatment with 3 μM methyl viologen (MV), leaf discs from SP and EP plants showed approximately 33 and 15% less damage than non-transformed (NT) plants. When 300 μM MV was sprayed onto whole plants, the photosynthetic activity of SP plants decreased by 25%, whereas that of NT plants decreased by 60%. In addition, SP plants showed enhanced tolerance to high temperature at 42 °C. After treatment at high temperature, the photosynthetic activity of SP plants decreased by about 7% compared to plants grown at 25 °C, whereas it declined by 31% in NT plants. These results indicate that transgenic potato can efficiently regulate oxidative stress from various environmental stresses via overexpression of At2-Cys Prx under control of the stress-inducible SWPA2 promoter.

Simultaneous expression of choline oxidase, superoxide dismutase and ascorbate peroxidase in potato plant chloroplasts provides synergistically enhanced protection against various abiotic stresses

Plants synthesize compatible solutes such as glycinebetaine (GB) in response to abiotic stresses. To evaluate the synergistic and protective effect of GB, transgenic potato plants expressing superoxide dismutase (SOD) and ascorbate peroxidase (APX) targeting to chloroplasts (referred to as SSA plants) were retransformed with a bacterial choline oxidase (codA) gene to synthesize GB in chloroplast in naturally occurring non-accumulator potato plants (including SSA) under the control of the stress-inducible SWPA2 promoter (referred to as SSAC plants). GB accumulation resulted in enhanced protection of these SSAC plants and lower levels of H(2)O(2) compared with SSA and non-transgenic (NT) plants after methyl viologen (MV)-mediated oxidative stress. Additionally, SSAC plants demonstrated synergistically enhanced tolerance to salt and drought stresses at the whole-plant level. GB accumulation in SSAC plants helped to maintain higher activities of SOD, APX and catalase following oxidative, salt and drought stress treatments than is observed in SSA and NT plants. Conclusively, GB accumulation in SSAC plants along with overexpression of antioxidant genes rendered the plants tolerant to multiple environmental stresses in a synergistic fashion.

Stress-induced expression of choline oxidase in potato plant chloroplasts confers enhanced tolerance to oxidative, salt, and drought stresses

Transgenic potato plants (Solanum tuberosum L. cv. Superior) with the ability to synthesize glycinebetaine (GB) in chloroplasts (referred to as SC plants) were developed via the introduction of the bacterial choline oxidase (codA) gene under the control of an oxidative stress-inducible SWPA2 promoter. SC1 and SC2 plants were selected via the evaluation of methyl viologen (MV)-mediated oxidative stress tolerance, using leaf discs for further characterization. The GB contents in the leaves of SC1 and SC2 plants following MV treatment were found to be 0.9 and 1.43 micromol/g fresh weight by HPLC analysis, respectively. In addition to reduced membrane damage after oxidative stress, the SC plants evidenced enhanced tolerance to NaCl and drought stress on the whole plant level. When the SC plants were subjected to two weeks of 150 mM NaCl stress, the photosynthetic activity of the SC1 and SC2 plants was attenuated by 38 and 27%, respectively, whereas that of non-transgenic (NT) plants was decreased by 58%. Under drought stress conditions, the SC plants maintained higher water contents and accumulated higher levels of vegetative biomass than was observed in the NT plants. These results indicate that stress-induced GB production in the chloroplasts of GB non-accumulating plants may prove useful in the development of industrial transgenic plants with increased tolerance to a variety of environmental stresses for sustainable agriculture applications.

Bitrophic and tritrophic effects of Bt Cry3A transgenic potato on beneficial, non-target, beetles

Insect-resistant transgenic plants have been suggested to have unpredictable effects on the biodiversity of the agro-ecosystem, including potential effects on insect natural enemies, beneficial in control of crop pests. Whilst carnivorous as adults, many of these predators may also consume plant tissues, in particular plant pollen and nectar. Coleoptera are important in terms of agro-ecological research not only because of the large number of species in this order, but also because of their role as biological control agents. Thus any detrimental impact on this group of insects would be highly undesirable. The effects of potato expressing the coleopteran-specific Bacillus thuringiensis delta-endotoxin Cry3A (Bt Cry3A) on the ladybird beetle Harmonia axyridis and the carabid beetle Nebria brevicollis were investigated via the bitrophic interaction of the adult ladybird with potato flowers and the tritrophic interaction of the carabid consuming a non-target potato pest. Immunoassays confirmed accumulation of the transgene product in potato leaves and floral tissues (at levels of up to 0.01% (pollen) and 0.0285% (anthers) of total soluble protein). Despite H. axyridis and N. brevicollis belonging to the targeted insect order, no significant effects upon survival or overall body mass change of either beetle were observed. Furthermore, Bt Cry3A had no detrimental effects on reproductive fitness of either beetle species, either in terms of fecundity or subsequent egg viability. Behavioural analysis revealed no significant impact of Bt Cry3A on beetle activity or locomoter behaviour. Ligand blots indicate that this is due to either the absence of Bt-binding sites in brush border membrane vesicles (BBMV) isolated from Nebria brevicollis, or in the case of Harmonia axyridis, the binding did not functionally lead to behavioural or physical effects.

Engineering resistance to PVY in different potato cultivars in a marker-free transformation system using a 'shooter mutant' A. tumefaciens

In this work, Potato virus Y (PVY) resistant potatoes were generated using an environmentally safe construct. For this purpose, a 'shooter' mutant Agrobacterium-based transformation system was used. The isopentenyl transferase gene (ipt) present on the Ti plasmid of 'shooter' strains enhances shoot regeneration and can be used as a phenotypic selection marker. The introduced marker-free binary vector carried a hairpin construct derived from the coat protein gene of PVY-NTN strain in order to induce gene silencing. Transformation resulted in high regeneration rates (1.4-5.7 shoots per explant). With pre-selection for the ipt (+) phenotype the transformation frequency was 24-53%, while without selection 12-28% of the shoots were PCR positive. The presence of the transgene was verified by Southern hybridization. In 16 of 31 challenged transformant lines PVY could be detected neither by RT-PCR nor by back inoculation. A 62.5% of these resistant lines proved to be also ipt-free. This transformation system was reproducible in four potato cultivars, suggesting that it could easily be adapted for other species.

Diploid potato (Solanum tuberosum L.) as a model crop to study transgene expression

This paper presents a method of Agrobacterium-mediated transformation for two diploid breeding lines of potato, and gives a detailed analysis of reporter gene expression. In our lab, these lines were also used to obtain tetraploid somatic hybrids. We tested four newly prepared constructs based on the pGreen vector system containing the selection gene nptII or bar under the 35S or nos promoter. All these vectors carried gus under 35S. We also tested the pDM805 vector, with the bar and gus genes respectively under the Ubi1 and Act1 promoters, which are strong for monocots. The selection efficiency (about 17%) was highest in the stem and leaf explants after transformation with pGreen where nptII was under 35S. About half of the selected plants were confirmed via PCR and Southern blot analysis to be transgenic and, depending on the combination, 0 to 100% showed GUS expression. GUS expression was strongest in multi-copy transgenic plants where gus was under Act1. The same potato lines carrying multi-copy bar under Ubi1 were also highly resistant to the herbicide Basta. The suggestion of using Agrobacterium-mediated transformation of diploid lines of potato as a model crop is discussed herein.

Potato in the age of biotechnology

Biotechnology-based tools are now widely used to enhance and expand the traditional remit of potato in food production. By modifying its functionality, the capacity of the potato to produce, for example, therapeutic or industrial compounds is now a reality, and its ability to resist disease can also be radically improved. Two developments have been crucial to expanding the role of potato: the recent advances in the fields of structural and functional potato genomics and the ability to integrate genes of interest into the potato genome. In this review we discuss how both developments have diversified the remit of this crop.

Evaluation of glycoalkaloids in tubers of genetically modified virus Y-resistant potato plants (var. Désirée) by non-aqueous capillary electrophoresis coupled with electrospray ionization mass spectrometry (NACE-ESI-MS)

The glycoalkaloid content of transgenic potatoes was evaluated by an optimised method based on non-aqueous capillary electrophoresis coupled on-line with electrospray ionization-mass spectrometry (NACE-ESI-MS). The potato material consisted of tubers from a conventional cv. Désirée and from three lines of modified plants resistant, intermediate and susceptible to infection by potato virus Y (PVY). The main glycoalkaloids were confirmed to be alpha-solanine and alpha-chaconine with parent ion masses m/z 852 and 868, respectively. In addition, an unknown minor peak at m/z 850.6 was found both in conventional (control) and susceptible line potato tubers. Such a compound exhibited an MS(2) spectrum with fragments ions at 704 and 396 m/z derived by loss of two ions, i.e. m/z 146 and 307, most likely corresponding to a rhamnose unit and a [glucose-(rhamnose)(2)] moiety, respectively. Up to 30-80-fold higher concentrations of total glycoalkaloids were found in the peel compared to flesh samples of all tubers examined. TGA content was nearly doubled in peel samples of resistant compared to control lines, and these levels were lower than the limit recommended for food safety, i.e. 20-60 mg of TGA per 100 g fresh weight. Moreover, it was established that tubers produced by virus-resistant clones are substantially equivalent in glycoalkaloid contents to those produced by conventional potato varieties.

Influence of plant development and environment on transgene expression in potato and consequences for insect resistance

Clonal replicates of different transformed potato plants expressing transgene constructs containing the constitutive Cauliflower Mosaic Virus (CaMV) 35S promoter, and sequences encoding the plant defensive proteins snowdrop lectin (Galanthus nivalis agglutinin; GNA), and bean chitinase (BCH) were propagated in tissue culture. Plants were grown to maturity, at first under controlled environmental conditions, and later in the glasshouse. For a given transgene product, protein accumulation was found to vary between the different lines of clonal replicates (where each line was derived from a single primary transformant plant), as expected. However, variability was also found to exist within each line of clonal replicates, comparable to the variation of mean expression levels observed between the different clonal lines. Levels of GNA, accumulated in different parts of a transgenic potato plant, also showed variation but to a lesser extent than plant-plant variation in expression. With the majority of the clonal lines investigated, accumulation of the transgene product was found to increase as the potato plant developed, with maximum levels found in mature plants. The variation in accumulation of GNA among transgenic plants within a line of clonal replicates was exploited to demonstrate that the enhanced resistance towards larvae of the tomato moth, Lacanobia oleracea L., caused by expression of this protein in potato, was directly correlated with the level of GNA present in the plants, and that conditions under which the plants were grown affect the levels of GNA expression and subsequent levels of insect resistance.

Control of enzymatic browning in potato (Solanum tuberosum L.) by sense and antisense RNA from tomato polyphenol oxidase

Polyphenol oxidase (PPO) activity of Russet Burbank potato was inhibited by sense and antisense PPO RNAs expressed from a tomato PPO cDNA under the control of the 35S promoter from the cauliflower mosaic virus. Transgenic Russet Burbank potato plants from 37 different lines were grown in the field. PPO activity and the level of enzymatic browning were measured in the tubers harvested from the field. Of the tubers from 28 transgenic lines that were sampled, tubers from 5 lines exhibited reduced browning. The level of PPO activity correlated with the reduction in enzymatic browning in these lines. These results indicate that expression of tomato PPO RNA in sense or antisense orientation inhibits PPO activity and enzymatic browning in the major commercial potato cultivar. Expression of tomato PPO RNA in sense orientation led to the greatest decrease in PPO activity and enzymatic browning, possibly due to cosuppression. These results suggest that expression of closely related heterologous genes can be used to prevent enzymatic browning in a wide variety of food crops without the application of various food additives.

Digestive proteolytic activity in larvae of tomato moth, Lacanobia oleracea; effects of plant protease inhibitors in vitro and in vivo

Three distinct digestive protease activities, with strongly alkaline pH optima, were identified in the gut of tomato moth (Lacanobia oleracea) larvae, and characterised using specific synthetic substrates and inhibitors. These were; a trypsin-like activity, a chymotrypsin-like activity specific for substrates and inhibitors containing more than one amino acid residue, and an elastase-like activity, accounting for 40%, 30% and 20% of overall proteolysis respectively. The protease activities differed in their sensitivities to inhibition by different plant protein protease inhibitors (PIs), as estimated by I(50) values. Soya bean Kunitz trypsin inhibitor (SKTI) was the only plant PI tested to inhibit all three digestive protease activities at concentrations <40 &mgr;g/ml (approx. 5x10(-6)M). Incorporation of SKTI into a potato leaf-based artificial diet at 2% of total protein, decreased larval survival and growth (by approx. 33% and 40% respectively after 21 days) and retarded development (by approx. 2 days). However, when SKTI was expressed in transgenic potato plants at approx. 0.5% of total protein, only marginal effects on L. oleracea larvae were observed, which decreased with time. Whilst the presence of SKTI in artificial diet increased endogenous larval trypsin-like activity by up to four-fold, no effects on this activity were observed in larvae feeding on transgenic plants.

Reduced Field Spread of Potato Leafroll Virus in Potatoes Transformed with the Potato Leafroll Virus Coat Protein Gene

Russet Burbank potato was transformed with plant expression vectors containing the potato leafroll luteovirus (PLRV) coat protein (CP) gene. Transgenic potato lines contained a gene expression cassette with two copies of a PLRV CP gene in which the nucleotide sequence was modified to improve expression of the gene. In addition, the two copies of the PLRV CP gene were each driven by a different promoter. Field test screening for PLRV resistance identified 15 lines which showed moderate resistance to PLRV infection and virus titer build-up and a longer incubation period for systemic infection. By conducting field resistance assays during a period when the vector of PLRV was not present, it was possible to test whether the observed resistance was sufficient to restrict aphid transmission of PLRV in a field test. Two years of field testing demonstrated that PLRV-spread from an infected plant to adjacent healthy plants of the same line was severely restricted in nearly all the transgenic lines in the field. These lines have useful resistance to PLRV and could aid in managing PLRV disease in Russet Burbank potato.

Effects of snowdrop lectin (GNA) delivered via artificial diet and transgenic plants on the development of tomato moth (Lacanobia oleracea) larvae in laboratory and glasshouse trials

The effects of snowdrop lectin (Galanthus nivalis agglutinin, GNA) on Lacanobia oleracea larval growth, development, consumption, and survival, were examined by 3 distinct bioassay methods. Larvae were reared on artificial diet containing GNA at 2% (w/w) dietary protein; on excised leaves of transgenic potato expressing GNA at approx. 0.07% of total soluble proteins; and on transgenic potato plants expressing GNA at approx. 0.6% of total soluble proteins in glasshouse trials. Significant effects on larval growth were observed with all three treatments. At 21days after hatch mean larval biomass was reduced by 32 and 23%, in the artificial diet and excised leaf bioassays respectively. In glasshouse trials a 48% reduction in insect biomass per plant was observed after 35days. The artificial diet and excised leaf assays also showed that GNA significantly slowed larval development as assessed by instar duration. GNA caused a 59% overall reduction in mean daily consumption in the artificial diet assay, and a significant reduction in leaf damage in glasshouse trials. However, prolonged compensatory feeding by larvae in the excised leaf assay resulted in their consuming 15% more total leaf material than the control group. Adaptation to low levels of GNA, in terms of biomass recovery and compensatory feeding, was observed within one larval generation in the detached leaf assay. No significant effects of GNA on larval survival were observed in the artificial diet and detached leaf bioassays, whereas survival was decreased by approx. 40% in the glasshouse bioassay. The assays show that the insecticidal effects of GNA can be observed both in vitro when fed in artificial diet and in planta, and can be demonstrated in the glasshouse as well as under growth cabinet conditions.

Characterization of acquired resistance in lesion-mimic transgenic potato expressing bacterio-opsin

The lesion-mimic mutants of certain plants display necrotic lesions resembling those of the hypersensitive response and activate local and systemic defense responses in the absence of pathogens. We have engineered a lesion-mimic phenotype in transgenic Russet Burbank potato plants through constitutive expression of a bacterio-opsin (bO) proton pump derived from Halobacterium halobium. Transgenic potato plants exhibiting a lesion-mimic phenotype had increased levels of salicylic acid and overexpressed several pathogenesis-related messenger RNAs, all hallmarks of systemic acquired resistance (SAR). The lesion-mimic plants also displayed enhanced resistance to the US1 isolate (A1 mating type) of a fungal pathogen, Phytophthora infestans, a causal agent of late blight disease. In contrast, little resistance was observed against the US8 isolate (A2 mating type) of this pathogen. Furthermore, a majority of the transgenic plants displaying the lesion-mimic phenotype had increased susceptibility to potato virus X. The tubers of these plants were not resistant to the bacterial pathogen Erwinia carotovora. These results indicate that expression of bO can result in the activation of defense responses in transgenic potato plants and show for the first time that bO expression can confer resistance to a pathogenic fungus. However, our results also demonstrate that like SAR, this "engineered" resistance is likely to be limited to certain pathogens and particular cultivars.

Genetically improved potatoes: protection from damage by Colorado potato beetles

Russet Burbank potato plants have been genetically improved to resist insect attack and damage by Colorado potato beetles (Leptinotarsa decemlineata (Say)) by the insertion of a cryIIIA gene encoding the insect control protein of Bacillus thuringiensis var. tenebrionis. A modified gene that dramatically improved plant expression of this protein was utilized. Its expression in Russet Burbank potato plants resulted in protection from damage by all insect stages in the laboratory and in dramatic levels of protection at multiple field locations. Analysis of these genetically modified potatoes indicated that they conform to the standards for Russet Burbank potatoes in terms of agronomic and quality characteristics including taste.