Abstract
Gallic acid (GA), an important polyphenolic compound in the plant, is a well-known antioxidant, antihyperglycemic, and anti-lipid peroxidative agent. Recently, GA treatment exhibited ameliorative effects on plants in response to some abiotic stresses. However, the elicitation effect of GA on plant defense against herbivorous insects has not yet been reported. In this study, we found that the exogenous application of GA induced the direct defense of tea plant (Camellia sinensis) against tea geometrid (Ectropis obliqua) larvae, through activating jasmonic acid (JA) signaling and phenylpropanoid pathways. These signaling cascades resulted in the efficient induction of several defensive compounds. Among them, astragalin, naringenin, and epigallocatechin-3-gallate were the three of the most active anti-feeding compounds. However, the exogenous GA treatment did not affect the preference of E. obliqua female moths and larval parasitoid Apanteles sp. Our study suggests that GA may serve as an elicitor that triggers a direct defense response against tea geometrid larvae in tea plants. This study will help to deepen the understanding of the interaction between plants and phytophagous insects and also provide theoretical and technical guidance for the development of plant defense elicitors.
Highlights
During the long course of co-evolution with insect herbivores, plants have evolved a series of induced defense mechanisms to cope with herbivore attacks (Howe and Jander, 2008; Wu and Baldwin, 2010)
We found that the exogenous application of Gallic acid (GA) enhanced the direct defense of tea plants to tea geometrid caterpillars, upregulated the expression levels of defensive genes related to jasmonic acid (JA) singling and phenylpropanoid pathways, and resulted in an efficient induction of defensive compounds, which will provide theoretical and technical guidance for the development of plant defense elicitors
The results showed that the exogenous application of GA to tea plants significantly reduced the weight gain of larvae by 14.8 and 26.8% at 9 and 13 days, respectively, compared with control (Figure 1)
Summary
During the long course of co-evolution with insect herbivores, plants have evolved a series of induced defense mechanisms to cope with herbivore attacks (Howe and Jander, 2008; Wu and Baldwin, 2010). The network reshapes the transcriptomes, proteomes, and metabolomes, resulting in the production of defensive compounds, such as secondary metabolites, protein inhibitors, and herbivore-induced plant volatiles (HIPVs), which in turn increase the direct or indirect resistance of plants to herbivores (Wu and Baldwin, 2010; GA Induces Defense of Tea. Schuman and Baldwin, 2016; Wang et al, 2020). Many active elicitors trigger defense responses by boosting hormonal signaling pathways, thereby regulating plant resistance against herbivores (Li et al, 2018; Xin et al, 2019; Chen et al, 2020), while a newly reported chemical elicitor 4-fluorophenoxyacetic acid was found to increase plant resistance by modulating the production of peroxidases, H2O2, and flavonoids, and directly triggering the formation of flavonoid polymers without affecting the canonical hormonal pathways (Wang et al, 2020). It is still necessary to identify new chemical elicitors that induce plant defenses against herbivores and reveal the underlying mechanisms, which would be beneficial for insights into the precise mechanisms of induced defense and developing new pest control strategies
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