Abstract
Larvae of the tobacco budworm 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. 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 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. Sequence tags from each treatment were aligned separately with the assembly to measure expression. The resulting table of differential expression had >22,000 assemblies each with a distinct combination of annotation and expression. Within these assemblies >1,400 were upregulated and >1,500 downregulated by immune activation with bacteria or fungi. Orthologs to innate immune components of other insects were identified including pattern recognition, signal transduction pathways, antimicrobial peptides and enzymes, melanization and coagulation. Additionally orthologs of components regulating hemocytic functions such as autophagy, apoptosis, phagocytosis and nodulation were identified. Associated cellular oxidative defenses and detoxification responses were identified providing a comprehensive snapshot of the early response to elicitation.
Highlights
Larvae of noctuid moths are major polyphagous pests of commodity crops such as maize, cotton, soybeans, alfalfa and vegetables throughout the world [1]
In this study we applied the technique of Illumina RNA-seq digital expression profiling to construct a hemocyte-specific de novo transcriptome, comprising >22,000 putative transcripts, against which we profiled the in vivo antimicrobial responses of hemocytes infected with bacterial or fungal elicitors within the first hours of infection
In this report we describe RNA-seq expression profiling of larval H. virescens hemocyte response to microbial elicitation in vivo
Summary
Larvae of noctuid moths are major polyphagous pests of commodity crops such as maize, cotton, soybeans, alfalfa and vegetables throughout the world [1]. In North America and in Brazil larvae of the tobacco budworm, Heliothis virescens (F.) are major pests of agricultural production, feeding on cotton, maize, and soybean, as well as fruits, vegetables and ornamentals [2,3]. Insects command an exquisitely evolved and powerful innate, i.e., germ-line encoded, immune response to microbial invasion which is divided between cellular and noncellular defenses [10]. Noncellular responses primarily involve the secretion of antimicrobial peptides, enzymes and other compounds into the hemocoel from immune-responsive tissues, while cellular responses are performed by several classes of hemocytes circulating within the hemocoel [11,12]. An immune response is initiated against infectious non-self when Microbe-Associated Molecular Patterns H. virescens by identification of antimicrobial response orthologs to baculoviral, bacterial and fungal infection [8,21±23]. In this study we applied the technique of Illumina RNA-seq digital expression profiling to construct a hemocyte-specific de novo transcriptome, comprising >22,000 putative transcripts, against which we profiled the in vivo antimicrobial responses of hemocytes infected with bacterial or fungal elicitors within the first hours of infection
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