Abstract
The wide-spread culture of transgenic Bt cotton resisting the infamous cotton bollworms has reduced the adoption of broad-spectrum insecticides to a large extent. Consequently, the non-targeted insect Adelphocoris suturalis Jakovlev has become a major cotton pest in China. Entomopathogenic microbes show promising results for controlling this pest in the future, but A. suturalis innate immune responses to these pathogens are poorly understood. Here, we used the entomopathogenic fungus Beauveria bassiana and the Gram-negative pathogenic bacteria Enterobactor cloacae to infect A. suturalis nymphs, followed by high throughput RNA-seq to analyze the immune transcriptomes of A. suturalis in response to the two pathogens. A total of 150 immunity-related genes were identified, including pattern recognition receptors, extracellular signal modulators, signal pathways (Toll, IMD, JNK, and JAK/STAT), and response effectors. Further quantitative real-time PCR analysis demonstrated that B. bassiana and E. cloacae were recognized by different receptors (GNBP and PGRP, respectively); activated Toll pathway and IMD pathway respectively; and both induced expression of the effector gene Defensin. However, melanization is suppressed in B. bassiana-infected nymphs. Collectively, this study provides a transcriptomic snapshot of the A. suturalis immune system, and at the genetic level, gains multifaceted insights of the immune response to fungal and Gram-negative bacterial pathogens. Ultimately this work pioneers the study of molecular mechanisms underlying immune interactions between A. suturalis and its pathogens and assists in the development of novel mitigation strategies to control this pest.
Highlights
Over the past two decades in China, transgenic cottons expressing Bacillus thuringiensis (Bt) toxins have been widely cultured to resist the refractory cotton bollworm Helicoverpa armigera (Wu et al, 2008)
The survival curves of nymphs infected by E. cloacae and B. bassiana were significantly lower than that of the mock control, demonstrating that A. suturalis is very sensitive to these two pathogens
The LT50 of nymphs infected by E. cloacae was 12 h, and 84 h for nymphs infected by B. bassiana, indicating that E. cloacae has a more efficient lethality to A. suturalis than B. bassiana
Summary
Over the past two decades in China, transgenic cottons expressing Bacillus thuringiensis (Bt) toxins have been widely cultured to resist the refractory cotton bollworm Helicoverpa armigera (Wu et al, 2008) This wide-spread control measure substantially reduced the adoption of broad-spectrum insecticides, decreasing selection pressure over Bt-insensitive mirid bug species. Many studies have focused on A. suturalis ecology and physiology (Lu et al, 2011; Zhang et al, 2011; Feng et al, 2012; Luo et al, 2017a),reporting its transcriptomes at different developmental stages and pheromone biosynthesisrelated genes (Luo et al, 2014; Tian et al, 2015) Together these reports identified candidate genes for further transgenic plants development. The immune responses regarding the interactions between A. suturalis and microbial pathogens, remain poorly understood
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