Isolation of transcripts from Diabrotica virgifera virgifera LeConte responsive to the Bacillus thuringiensis toxin Cry3Bb1

Abstract

Crystal (Cry) proteins derived from Bacillus thuringiensis (Bt) have been widely used as a method of insect pest management for several decades. In recent years, a transgenic corn expressing the Cry3Bb1 toxin has been successfully used for protection against corn rootworm larvae (genus Diabrotica). The biological action of the Bt toxin in corn rootworms has not yet been clearly defined. Because development of resistance to Bt by corn rootworms will have huge economic and ecological costs, insight into larval response to Bt toxin is highly desirable. We identified 19 unique transcripts that are differentially expressed in D. virgifera virgifera larvae reared on corn transgenic for Cry3Bb1. Putative identities of these genes were consistent with impacts on metabolism and development. Analysis of highly modulated transcripts resulted in the characterization of genes coding for a member of a cysteine-rich secretory protein family and a glutamine-rich membrane protein. A third gene that was isolated encodes a nondescript 132 amino acid protein while a fourth highly modulated transcript could not be further characterized. Expression patterns of these four genes were strikingly different between susceptible and resistant western corn rootworm populations. These genes may provide useful targets for monitoring of Bt exposure patterns and resistance development in pest and non-target insect populations.

Intestinal regeneration as an insect resistance mechanism to entomopathogenic bacteria

“…Genes with reduced expression were involved in diverse metabolic pathways, suggesting shutdown of digestion and a concomitant up-regulation of energy production through respiration in response to intoxication. A similar response was observed in larvae of western corn rootworm, Diabrotica virgifera virgifera , during exposure to Cry3Bb [50]. Interestingly, alteration in gene expression in T. molitor almost ceased after 24 h, supporting tight control of the midgut response to intoxication [49 • ].…”

Transcriptome Profiling of the Intoxication Response of Tenebrio molitor Larvae to Bacillus thuringiensis Cry3Aa Protoxin

“…We were able to determine through GO term analysis that Cry3Aa-intoxication resulted in an induction of genes involved in mitochondrial electron transport, signalling, carbohydrate metabolism, membrane components, cell structure, and allergens, while those encoding metabolic enzymes associated with proteolysis, glycolysis, TCA, and fatty acid metabolism were repressed. Similarly, enzymes involved in cellulose degradation were down-regulated in Diabrotica virgifera larvae exposed corn roots expressing Cry3Bb [42]. In insects undergoing intoxication, cessation of feeding may result in the down-regulation of digestive-associated processes and up-regulation of energy production via cellular respiration.…”

“…Therefore, while C. fumiferana and M. sexta larvae exposed to sublethal doses of Cry1Ab protoxin displayed the most significant differential gene expression between two and five hours post intoxication [14], we chose to expose T. molitor larvae to a lethal dose of Cry3Aa protoxin for 24 h before performing RNA-Seq to ensure all larvae had sufficient exposure to the protoxin, and to ensure mRNA was harvested well in advance of the onset of mortality [20]. The same incubation period was used to characterize Cry3Bb intoxication in another coleopteran pest, D. virgifera [42]. Data from the RNA-Seq experiment provided sequence information for the design of microarrays, as well as a snapshot of transcription 24 h post intoxication.…”

Patterns of Gene Expression in Western Corn Rootworm (Diabrotica virgifera virgifera) Neonates, Challenged with Cry34Ab1, Cry35Ab1 and Cry34/35Ab1, Based on Next-Generation Sequencing

“…Like other stressors, the Bt toxins induced changes in WCR gene expression [17,27,28,29]. However, the number of genes altered and GO terms enriched vary greatly with the source of challenge and target organism [16,17,24,28,30], exposure time [18], and even within different populations of the same species. For example, in two Cry1Ac resistant Plutella xylostella populations originating from different collections, the number of enriched GO terms associated with each population was markedly different [17].…”