Abstract
In response to insect herbivory, plants emit elevated levels of volatile organic compounds for direct and indirect resistance. However, little is known about the molecular and genomic basis of defense response that insect herbivory trigger in cotton plants and how defense mechanisms are orchestrated in the context of other biological processes. Here we monitored the transcriptome changes and volatile characteristics of cotton plants in response to cotton bollworm (CBW; Helicoverpa armigera) larvae infestation. Analysis of samples revealed that 1,969 transcripts were differentially expressed (log2|Ratio| ≥ 2; q ≤ 0.05) after CBW infestation. Cluster analysis identified several distinct temporal patterns of transcriptome changes. Among CBW-induced genes, those associated with indirect defense and jasmonic acid pathway were clearly over-represented, indicating that these genes play important roles in CBW-induced defenses. The gas chromatography-mass spectrometry (GC-MS) analyses revealed that CBW infestation could induce cotton plants to release volatile compounds comprised lipoxygenase-derived green leaf volatiles and a number of terpenoid volatiles. Responding to CBW larvae infestation, cotton plants undergo drastic reprogramming of the transcriptome and the volatile profile. The present results increase our knowledge about insect herbivory-induced metabolic and biochemical processes in plants, which may help improve future studies on genes governing processes.
Highlights
In response to insect herbivory, plants emit elevated levels of volatile organic compounds for direct and indirect resistance
We observed that 9% genes were commonly expressed in response to cotton bollworm (CBW) feeding over the 48 h time course
Many genes were exclusively expressed at 6 h after the onset of CBW infestation, which indicates that these genes are likely to play roles in the herbivory-induced early signaling events
Summary
In response to insect herbivory, plants emit elevated levels of volatile organic compounds for direct and indirect resistance. Among available methods for high-throughput analysis, microarray is a powerful tool for studies of gene expression in response to herbivory, and this approach has been applied in several plant species, notably Arabidopsis thaliana[5,6,7], Nicotiana attenuata[8,9] and rice[2,10]. These studies demonstrate that a plant’s response to herbivore infestation is associated with large-scale changes in gene expression, and three major plant hormones, jasmonic acid (JA), salicylic acid (SA) and ethylene (ET) are essential in herbivore-induced defense responses. In response to feeding of Anthonomus grandis, cotton plants activated a lot of genes involved in phytohormone signaling pathways to bolster resistance to future threats[20]
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