Resistance to Cry3Bb1 in the western corn rootworm (Diabrotica virgifera virgifera): RNA-seq & differential expression

The Western Corn Rootworm (WCR) Diabrotica virgifera virgifera is a major pest of corn. It has developed resistance mechanisms against most of the chemical compounds and cultural practices used to control it. One of the most recent events is the development of the resistance to transgenic corn expressing genes coding for toxins from Bacillus thuringiensis. The present study investigates molecular mechanisms involved in the resistance to Cry3Bb1 developed by this insect. For this purpose, WCR neonates from two strains were considered, one susceptible and one resistant to the toxin. Larvae were exposed either to Cry3Bb1-expressing corn or non-transgenic near-isoline corn for 4 or 8 continuous hours. Total RNA was extracted and sequenced for a transcriptomic approach. The sequencing reads were aligned to a reference transcriptome in order to perform a statistical analysis of differential expression. The results show different levels of expression between strains for transcripts corresponding to proteins such as ABC transporters, amylases, proteases and protease inhibitors, detoxifying enzymes (cytochrome P450) and immune related proteins. The results also show that the number of significantly differentially expressed transcripts between susceptible and resistant strains is low after 4 hours of exposure but increases greatly after 8 hours. The proteins corresponding to the identified transcripts are consistent with previous results on the mode of action and resistance mechanisms of Bt toxins in other Coleoptera, Lepidoptera and Diptera. These proteins have been identified as receptors, activators or inhibitors of Cry toxins.