Engineered Expression of Vip3A in Green Tissues as a Feasible Approach for the Control of Insect Pests in Maize

SIMPLE SUMMARY: The use of genetically modified (GM) crops expressing Bacillus thuringiensis (Bt) proteins is currently the most common method for controlling herbivorous pests. However, the insecticidal proteins in the edible tissues of transgenic crops has become an issue of intense public concern. We developed an available strategy based on the Cre/loxP-mediated system for manipulating Vip3A expression in maize defined green tissues outside edible parts to relieve public concerns. To test this approach, two basic transgenic maize named KEY and LOCK containing Cre and Vip3A, were generated, respectively. By crossing the KEY and LOCK plants, the expression of blocked Vip3A was enabled in specific green tissues in their hybrids. After assessing the insect-resistance of the transgenic maize in the laboratory and field, the KEY × LOCK hybrids showed high plant resistance levels against the two common lepidopteran pests. The present study suggested that the Cre/loxP-mediated genetic engineering approach would be crucial in ensuring the biosafety of GM plants, and also provided an effective strategy for manipulating transgene expression in specific tissues. ABSTRACT: Genetic engineering technology offers opportunities to improve many important agronomic traits in crops, including insect-resistance. However, genetically modified (GM) exogenous proteins in edible tissues of transgenic crops has become an issue of intense public concern. To advance the application of GM techniques in maize, a Cre/loxP-based strategy was developed for manipulating the transgenes in green tissues while locking them in non-green tissues. In the strategy, the site-specific excision can be used to switch on or off the expression of transgenes at specific tissues. In this work, two basic transgenic maize, named KEY, carrying the Cre gene, and LOCK, containing the Vip3A gene with a blocked element, were obtained based on their separate fusion gene cassettes. The expression level and concentration of Vip3A were observed with a high specific accumulation in the green tissues (leaf and stem), and only a small amount was observed in the root and kernel tissues in the KEY × LOCK hybrids. The insect resistance of transgenic maize against two common lepidopteran pests, Ostrinia furnacalis and Spodoptera frugiperda, was assessed in the laboratory and field. The results indicate that the hybrids possessed high resistance levels against the two pests, with mortality rates above 73.6% and damage scales below 2.4 compared with the control group. Our results suggest that the Cre/loxP-mediated genetic engineering approach has a competitive advantage in GM maize. Overall, the findings from this study are significant for providing a feasible strategy for transgenes avoiding expression in edible parts and exploring novel techniques toward the biosafety of GM plants.