Evaluation of potato tuber moth (Lepidoptera: Gelechiidae) resistance in tubers of Bt-cry5 transgenic potato lines

Green-tissue-specific, C(4)-PEPC-promoter-driven expression of Cry1Ab makes transgenic potato plants resistant to tuber moth (Phthorimaea operculella, Zeller)

An important strategy for obtaining a safer transgenic plant may be the use of a spatial- or tissue-specific promoter, instead of a constitutive one. In this study, we have used a light-inducible maize PEPC promoter to regulate the cry1Ab gene, aiming to produce transgenic potatoes that are resistant to potato tuber moth (PTM) (Phthorimaea operculella, Zeller). Out of 60 regenerated lines having normal phenotypes, 55 lines were PCR-positive for both the cry1Ab and nptII genes. Southern analysis on three selected putative transgenic lines revealed that they have only a single intact copy of the cry1Ab gene. An investigation of the Cry1Ab protein in the leaves and light-exposed (LE) tubers of the transgenic lines demonstrated the presence of the protein in the foliage and green tubers but not in the light-not exposed (LNE) tubers. A bioassay analysis of excised leaves of nine randomly selected lines showed that eight lines had 100% PTM larval mortality. Confirming results were obtained in six selected lines using the whole plant bioassay in the greenhouse. LE transgenic tubers also exhibited 100% larval mortality; however, the levels of damage to the LNE transgenic tubers were high and statistically the same as those incurred by the non-transgenic ones. Based on the results, we believe that this spatial expression of Cry1Ab using the light-inducible PEPC promoter can control PTM infestation in the field and significantly reduce pollution transmission to storage potatoes.

Expression of the cry9Aa2 B.t. gene in tobacco chloroplasts confers resistance to potato tuber moth

We report here the control of potato tuber moth (Phthorimaea operculella) by incorporating a truncated Bacillus thuringiensis cry9Aa2 gene in the plastid genome. Plasmids pSKC84 and pSKC85 are derivatives of a new polycistronic plastid transformation vector, pPRV312L, that carries spectinomycin resistance (aadA) as a selective marker and targets insertions in the trnI-trnA intergenic region. The Cry9Aa2 N-terminal region (82.1 kDa; 734 amino acids) was expressed in a cassette, which consists of 49 nucleotides of the cry9Aa2 leader and the 3'-untranslated region of the plastid rbcL gene (TrbcL), and relies on readthrough transcription from the plastid rRNA operon. In a tobacco leaf bioassay, expression of Cry9Aa2 conferred resistance to potato tuber moth. In accordance, the Cry9Aa2 insecticidal protein accumulated to high levels, approximately 10% of the total soluble cellular protein and approximately 20% in the membrane fraction. However, high-level Cry9Aa2 expression significantly delayed plant development. Thus, a practical system to control potato tuber moth by Cry9Aa2 expression calls for down-regulation of its expression.

Promoter and piggyBac activities within embryos of the potato tuber moth, Phthorimaea operculella, Zeller (Lepidoptera: Gelechiidae)

Potato production in tropical and subtropical countries suffers from damage caused by the potato tuber moth (PTM), Phthorimaea operculella. The aim of this research was the development of the components required for a germline transformation system for the PTM. We tested three components that are critical to genetic transformation systems for insects: promoter activity, marker gene expression, and transposable element function. We compared the transcriptional activities of five different promoters, hsp70, hsp82, actin5C, polyubiquitin and immediate early 1 gene (ie1), within PTM embryos. The ie1 promoter, flanked by the hr5 enhancer element, showed a very high level of transcriptional activity compared to the other promoters. The fluorescence activity of EGFP was also determined and transient expression of EGFP was detected in 57% of injected embryos. The transpositional activity of the piggyBac transposable element was tested in an interplasmid transposition assay. The piggyBac element was shown to be mobile within the embryonic soma of the PTM with a transposition frequency of 4.2 x 10(-5) transpositions/donor plasmid. Incorporating a transactivator plasmid expressing the immediate early protein (IE1) from the Bombyx mori nuclear polyhedrosis virus enhanced the efficiency of piggyBac mobility.

A hybrid Bacillus thuringiensis delta-endotoxin gives resistance against a coleopteran and a lepidopteran pest in transgenic potato

Expression of Bacillus thuringiensis delta-endotoxins has proven to be a successful strategy for obtaining insect resistance in transgenic plants. Drawbacks of expression of a single resistance gene are the limited target spectrum and the potential for rapid adaptation of the pest. Hybrid toxins with a wider target spectrum in combination with existing toxins may be used as tool to mitigate these problems. In this study, Desiree potato plants were genetically modified to resist attack by insect species belonging to the orders Coleoptera and Lepidoptera, through the insertion of such a hybrid gene, SN19. Transgenic plants were shown to be resistant against Colorado potato beetle larvae and adults, potato tuber moth larvae, and European corn borer larvae. These are the first transgenic plants resistant to pests belonging to two different insect orders. In addition, the target receptor recognition of this hybrid protein is expected to be different from Cry proteins currently in use for these pests. This makes it a useful tool for resistance management strategies.

Economic, ecological, food safety, and social consequences of the deployment of bt transgenic plants

Transgenic plants expressing insecticidal proteins from the bacterium, Bacillus thuringiensis (Bt), are revolutionizing agriculture. Bt, which had limited use as a foliar insecticide, has become a major insecticide because genes that produce Bt toxins have been engineered into major crops grown on 11.4 million ha worldwide in 2000. Based on the data collected to date, generally these crops have shown positive economic benefits to growers and reduced the use of other insecticides. The potential ecological and human health consequences of Bt plants, including effects on nontarget organisms, food safety, and the development of resistant insect populations, are being compared for Bt plants and alternative insect management strategies. Scientists do not have full knowledge of the risks and benefits of any insect management strategies. Bt plants were deployed with the expectation that the risks would be lower than current or alternative technologies and that the benefits would be greater. Based on the data to date, these expectations seem valid.