Compatibility of garlic (Allium sativum L.) leaf agglutinin and Cry1Ac δ-endotoxin for gene pyramiding

How well will stacked transgenic pest/herbicide resistances delay pests from evolving resistance?

Resistance has evolved to single transgenic traits engineered into crops for arthropod and herbicide resistances, and can be expected to evolve to the more recently introduced pathogen resistances. Combining transgenes against the same target pest is being promoted as the solution to the problem. This solution will work if used pre-emptively, but where resistance has evolved to one member of a stack, resistance should easily evolve for the second gene in most cases. We propose and elaborate criteria that could be used to evaluate the value of stacked traits for pest resistance management. Stacked partners must: target the same pest species; be in a tandem construct to preclude segregation; be synchronously expressed in the same tissues; have similar tissue persistence; target pest species that are still susceptible to at least two stacked partners. Additionally, transgene products must not be degraded in the same manner, and there should be a lack of cross-resistance to stacked transgenes or to their products. With stacked herbicide resistance transgenes, both herbicides must be used and have the same persistence. If these criteria are followed, and integrated with other pest management practices, resistance may be considerably delayed. © 2016 Society of Chemical Industry.

Penetration through the peritrophic matrix is a key to lectin toxicity against Tribolium castaneum

In the last decades lectins have received a lot of attention as potential tools in pest control. Despite substantial progress in the field not all the factors determining insecticidal potency and selectivity of these proteins have been described. Recently, three lectins, RSA (Rhizoctonia solani agglutinin), SNA-I and SNA-II (Sambucus nigra agglutinin I and II) have been shown to be toxic to aphids and caterpillars. In this project we investigated if these lectins are also toxic against larvae and a cell line of the red flour beetle, Tribolium castaneum, a model organism and important pest of stored products. Furthermore, we analyzed the stability of the lectins in the larval gut and used confocal microscopy to compare their efficiency in passing through the peritrophic matrix (PM). We observed that all three lectins were toxic against the T. castaneum cell line and their effectiveness in vitro was in decreasing order SNA-II>SNA-I>RSA with the respective EC50 being 0.1, 0.5 and 3.6 μg/ml. Larvae feeding for 16 day on diets containing 2% RSA, 2% SNA-II and 2% SNA-I weighed 0.14 ± 0.07 mg, 0.67 ± 0.44 mg and 1.89 ± 0.38 mg, corresponding to approximately 7%, 36% and 80% of control larvae, respectively. As a consequence, RSA increased the time to adult emergence by over 3-fold, SNA-II by 1.9-fold and SNA-I by 1.2-fold. RSA and SNA-II were stable in the larval gut, while SNA-I was digested and excreted with the feces. Finally, confocal microscopy confirmed that RSA passed through the PM more efficiently than SNA-II. In conclusion, our data suggest that the lectin ability to pass through the PM, governed by molecule dimensions, charge and size of PM pores, is one of the features that determine the toxicity of these insecticidal proteins.