Next‐generation transgenic cotton: pyramiding RNAi and Bt counters insect resistance

Abstract

SummaryTransgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) are extensively cultivated worldwide. To counter rapidly increasing pest resistance to crops that produce single Bt toxins, transgenic plant ‘pyramids’ producing two or more Bt toxins that kill the same pest have been widely adopted. However, cross‐resistance and antagonism between Bt toxins limit the sustainability of this approach. Here we describe development and testing of the first pyramids of cotton combining protection from a Bt toxin and RNA interference (RNAi). We developed two types of transgenic cotton plants producing double‐stranded RNA (dsRNA) from the global lepidopteran pest Helicoverpa armigera designed to interfere with its metabolism of juvenile hormone (JH). We focused on suppression of JH acid methyltransferase (JHAMT), which is crucial for JH synthesis, and JH‐binding protein (JHBP), which transports JH to organs. In 2015 and 2016, we tested larvae from a Bt‐resistant strain and a related susceptible strain of H. armigera on seven types of cotton: two controls, Bt cotton, two types of RNAi cotton (targeting JHAMT or JHBP) and two pyramids (Bt cotton plus each type of RNAi). Both types of RNAi cotton were effective against Bt‐resistant insects. Bt cotton and RNAi acted independently against the susceptible strain. In computer simulations of conditions in northern China, where millions of farmers grow Bt cotton as well as abundant non‐transgenic host plants of H. armigera, pyramided cotton combining a Bt toxin and RNAi substantially delayed resistance relative to using Bt cotton alone.

Gene silencing by RNAi via oral delivery of dsRNA by bacteria in the South American tomato pinworm, Tuta absoluta

“…A similar phenotype has been described for Tribolium castaneum larvae microinjected with dsRNA of the JH‐inducible Krüppel homolog‐1 gene; the larvae displayed remains of the old tegument attached to the body, undergoing an early metamorphosis to the pupae stage . Silencing another gene linked to JH metabolism, juvenile hormone‐binding protein, by feeding H. armigera on RNAi cotton plants increased larval mortality . Although silencing of JHP has not been previously reported in lepidopterans, our results with T. absoluta indicate that targeting this gene might be effective and promising in an RNAi control strategy.…”

“…One example is the use of a plant pyramidal transformation to express dsRNA of CHI and JHP or a mixture of bacteria expressing both genes (together or as a mixture of bacteria solution). Helicoverpa armigera fed on cotton plants expressing proteins Cry and dsRNA of juvenile hormone acid methyltransferase and juvenile hormone binding protein genes showed higher mortality when compared with larvae fed on plants with just one transgenic event …”

Plant‐mediated gene silencing of an essential olfactory‐related Gqα gene enhances resistance to grain aphid in common wheat in greenhouse and field

“…The principle of plant‐mediated RNAi is that it can silence the expression of key developmental or reproductive genes using exogenous dsRNA, which causes pest developmental stagnation or a direct lethal effect, finally achieving the purpose of controlling the target pest population. When an insect eats such transgenic plants, expression of the target gene can be significantly reduced, and this can function as a form of long‐lasting inhibition of pest growth . In recent years, important progress has been made in pest control strategies based on RNAi .…”

Genetically modified soybean expressing insecticidal protein (Cry1Ac): Management risk and perspectives

“…In Brazil, for example, studies demonstrated a high efficiency of the Bt soybean strain DAS-81419-2 (expressing two proteins) in the reduction of damage caused by A. gemmatalis, C. includens, H. virescens, and S. cosmioides during the vegetative and reproductive stages (Marques et al 2016). Recent studies have suggested the use of RNA interference as a promising alternative or complementary strategy for pest control and management (Asokan et al 2014;Kim et al 2015;Fishilevich et al 2016;Yu et al 2016;Ni et al 2017). …”

“…The technological solution to this problem is the production of transgenic plants expressing a higher number of Bt toxins, as indicated in the results obtained by Marques et al (2017), which show the high efficiency of a soybean variety containing two Bt toxins in the control of primary and secondary pests. The recommended strategies for controlling problematic pests are the cultivation of plants expressing genes for two or three Bt toxins, the expansion of refuge areas, and the use of other management tactics (Carrière et al 2016a(Carrière et al , 2016bNi et al 2017). …”