Knockdown of the MAPK p38 pathway increases the susceptibility of Chilo suppressalis larvae to Bacillus thuringiensis Cry1Ca toxin

Lin Qiu,Lang Liu,Weihua Ma,Xiaoping Wang,Boyao Zhang,Yongjun Lin,Jinxing Fan,Chaoliang Lei

doi:10.1038/srep43964

Abstract

The bacterium Bacillus thuringiensis (Bt) produces a wide range of toxins that are effective against a number of insect pests. Identifying the mechanisms responsible for resistance to Bt toxin will improve both our ability to control important insect pests and our understanding of bacterial toxicology. In this study, we investigated the role of MAPK pathways in resistance against Cry1Ca toxin in Chilo suppressalis, an important lepidopteran pest of rice crops. We first cloned the full-length of C. suppressalis mitogen-activated protein kinase (MAPK) p38, ERK1, and ERK2, and a partial sequence of JNK (hereafter Csp38, CsERK1, CsERK2 and CsJNK). We could then measure the up-regulation of these MAPK genes in larvae at different times after ingestion of Cry1Ca toxin. Using RNA interference to knockdown Csp38, CsJNK, CsERK1 and CsERK2 showed that only knockdown of Csp38 significantly increased the mortality of larvae to Cry1Ca toxin ingested in either an artificial diet, or after feeding on transgenic rice expressed Cry1Ca. These results suggest that MAPK p38 is responsible for the resistance of C. suppressalis larvae to Bt Cry1Ca toxin.

Highlights

Pore-forming toxins (PFT) play an important role in bacterial pathogenesis and the development of pest resistant strains of crops[1,2,3]
Mitogen-activated protein kinase (MAPK) signaling pathways are comprised of serine-threonine protein kinases that regulate a variety of cellular processes[28,29,30]
Since the activation of the p38 pathway by Cry5B toxin in Caenorhabditis elegans was first described[2], several studies have demonstrated that low doses of other PFTs can induce the activation of this pathway in cultured-epithelial cell lines[2,32]

Summary

Introduction

Pore-forming toxins (PFT) play an important role in bacterial pathogenesis and the development of pest resistant strains of crops[1,2,3]. The non-olfactory, odorant binding protein C12 has been reported to play a role in the resistance of Tribolium castaneum larvae to Cry3Ba and Cry23Aa/Cry37Aa toxins[9]. A few studies have focused on analyzing the roles of specific pathways and genes in resistance to Bt toxins. Previous studies have demonstrated that the Cry1Ca toxin is effective against this pest[26], and that transgenic Bt crops producing Cry1Ca (T1C-19) are resistant to C. suppressalis[27]. In this paper we present the results of experiments designed to determine the function of specific C. suppressalis MAPK pathway genes in resistance to Cry1Ca. The results suggest that the p38 pathway plays a major role in resistance to Cry1Ca toxin in C. suppressalis

Methods

Results

Conclusion