Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2012
Publication Date: 8/14/2012
Citation: Shelby, K., Popham, H.J. 2012. RNA-seq study of microbially induced hemocyte transcripts from larval Heliothis virescens (Lepidoptera: Noctuidae). Insects. 3:743-762.
Interpretive Summary: Budworm larvae are caterpillars that cause heavy economic loss to many agricultural commodities in North America and are closely related to the Old World bollworm that is an economic pest worldwide. We have developed a library of DNA sequences from this pest moth’s genome that encodes over 22,000 different genes. These sequences were screened for changes in expression in response to insect bacterial and fungal infection and many groups of genes were identified that changed significantly. This is a much larger library of sequences from this moth that change in response to infection than previously available and will be used worldwide by researchers. We will use the information to study genes that influence the immune system of the budworm which will lead us to what control measures work best and which measures the insect will adapt to in a short time.
Technical Abstract: Larvae of the tobacco budworm, Heliothis virescens, are major polyphagous pests throughout the Americas. Development of effective microbial biopesticides for this and related noctuid pests has been stymied by the natural resistance mediated innate immune response. Disruption or immunosuppression may be a promising control approach. Hemocytes play an early and central role in activating and coordinating immune responses to entomopathogens. To approach this problem we completed RNA-seq expression profiling of hemocytes collected from H. virescens larvae following an in vivo challenge with bacterial and fungal cell wall components to elicit an immune response. A de novo exome assembly was constructed by combination of sequence tags from all treatments against which sequence tags from each treatment were aligned to assess up- or downregulation by each treatment. The resulting table of differential expression had >22,000 assemblies each with a distinct combination of annotation and expression. Within these assemblies over 1400 were upregulated and >1500 downregulated by immune activation with bacteria or fungi. Over 700 H. virescens orthologs to innate immune components of other insects were identified, some of which were differentially regulated by immune elicitation. These included orthologs of pattern recognition, signal transduction pathways, antimicrobial peptides and enzymes, melanization and coagulation. Additionally H. virescens orthologs of components regulating hemocytic functions such as autophagy, apoptosis, phagocytosis and nodulation were identified. Additional components of the innate immune system and associated cellular oxidative defenses and detoxification responses were identified providing a comprehensive snapshot of the early response by larval hemocytes to microbial elicitation.