Abstract
Green leaf volatiles (GLV), which are rapidly emitted by plants in response to insect herbivore damage, are now established as volatile defense signals. Receiving plants utilize these molecules to prime their defenses and respond faster and stronger when actually attacked. To further characterize the biological activity of these compounds we performed a microarray analysis of global gene expression. The focus of this project was to identify early transcriptional events elicited by Z-3-hexenol (Z-3-HOL) as our model GLV in maize (Zea mays) seedlings. The microarray results confirmed previous studies on Z-3-HOL -induced gene expression but also provided novel information about the complexity of Z-3-HOL -induced transcriptional networks. Besides identifying a distinct set of genes involved in direct and indirect defenses we also found significant expression of genes involved in transcriptional regulation, Ca2+-and lipid-related signaling, and cell wall reinforcement. By comparing these results with those obtained by treatment of maize seedlings with insect elicitors we found a high degree of correlation between the two expression profiles at this early time point, in particular for those genes related to defense. We further analyzed defense gene expression induced by other volatile defense signals and found Z-3-HOL to be significantly more active than methyl jasmonate, methyl salicylate, and ethylene. The data presented herein provides important information on early genetic networks that are activated by Z-3-HOL and demonstrates the effectiveness of this compound in the regulation of typical plant defenses against insect herbivores in maize.
Highlights
The response of plants to insect herbivore damage is characterized by a massive reprogramming of metabolic pathway aiming towards the reduction of damage
Leaves were collected 20 and 60 min after exposure since the focus of this study was on early transcriptional changes induced by green leaf volatiles (GLV) based on our previous finding that showed maximum jasmonic acid (JA) accumulation after Z-3-HOL exposure between 10-30 min after exposure [41]
Based on the selection criteria described in Material and Methods we identified 20 genes with a ≥ 2fold increase or decrease in transcript levels 20 min after exposure to Z-3-HOL (Table S1)
Summary
The response of plants to insect herbivore damage is characterized by a massive reprogramming of metabolic pathway aiming towards the reduction of damage. HIPV play important roles as mediators of tritrophic interactions, for example by attracting natural enemies of the attacking insect herbivore and/or by serving as a repellent [14,15,16,17,18,19] Another function for these volatiles became apparent in recent years, when it was discovered that undamaged neighboring plants can “smell” some of these compounds that are emitted by damaged plants [20,21,22]. Maize seedlings that were previously exposed to GLV from neighboring plants produced significantly more JA and volatile sesquiterpenes upon subsequent treatment with IE when compared to appropriate controls This was the first report on priming against insect herbivory signaled by GLV and it was demonstrated that this effect is linked to anti-herbivore defenses since responses to mechanical wounding alone were not affected. The data presented provides evidence for the potential and importance of GLV to activate defensive measures in response to insect herbivory
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