Exogenous Application of Gallic Acid Induces the Direct Defense of Tea Plant Against Ectropis obliqua Caterpillars.

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.

Biological evidences for successive oogenesis and egg-laying of Matsumurasca onukii.

Tea plant (Camellia sinensis) is one of the most important horticultural cash crops, and tea green leafhopper (Matsumurasca onukii) is an extremely harmful sap-sucking pest of tea plant. Serious generation overlapping, which is mainly caused by the long oviposition period, leads to poor control effect of pesticides on this pest in the tea plantation. But the intuitive evidences of continuous oogenesis and egg-laying of this pest are still lacking, which seriously hindered the development of genetic control methods. Here, we clarified the main structures of the inner reproductive system of tea green leafhopper female adult. Oviposition behaviors were monitored as well, and six oviposition steps were recorded. According to the maturity of oocytes, the maturity stages of the reproductive system under different copulation periods were classified into 4 stages. For female adults at stage IV, mature and immature oocytes were presented simultaneously, and the developmental levels of oocytes were asynchronous among different ovarioles. The proportion of gravid females with mature oocytes significantly increased when the continuous copulation time was prolonged. In sync with the development of the ovary maturity, female adults started to slightly deposit eggs at the 5th day, and then increased dramatically. In addition, we found that, whether mature or immature, oocytes in the ovarioles always emitted green fluorescence under blue light excitation, which in turn provide solid proof for the new egg detection method from the insect physiology point of view.

A novel inhibitor of the JA signaling pathway represses herbivore resistance in tea plants.

The jasmonic acid (JA) signaling pathway plays a vital role in mediating plant resistance to herbivores. Tea plant (Camellia sinensis) is one of the most important woody cash crops in the world. Due to the lack of genetic transformation systems for tea plants, how the JA signaling pathway works in tea plants has not yet been determined. Now, with the development of cross-disciplines, chemical biology provides new means for analysing the JA signaling pathway. In the present study, the small molecule isoquinoline compound ZINC71820901 (lyn3) was obtained from the ZINC molecular library through virtual screening based on the structure of the crystal COI1-JAZ1 co-receptor and was found to act as an inhibitor of the JA signaling pathway both in Arabidopsis and tea plants. Our results revealed that lyn3 repressed tea plant resistance to Ectropis grisescens mainly by decreasing the accumulation of (-)-epicatechin (EC) and (-)-epigallocatechin (EGC) via repression of the JA signaling pathway, which functioned in the different modulation manner to the already known inhibitor SHAM. As a novel inhibitor of JA signaling pathway, lyn3 provides a specific option for further research on the JA pathway.

(+)-Catechin, epicatechin and epigallocatechin gallate are important inducible defensive compounds against Ectropis grisescens in tea plants.

The tea plant, Camellia sinensis (L.) O. Kuntze, is an economically important, perennial woody plant rich in catechins. Although catechins have been reported to play an important role in plant defences against microbes, their roles in the defence of tea plants against herbivores remain unknown. In this study, we allowed the larvae of Ectropis grisescens, a leaf-feeding pest, to feed on the plants, and alternatively, we wounded the plants and then treated them with E. grisescens oral secretions (WOS). Both approaches triggered jasmonic acid-, ethylene- and auxin-mediated signalling pathways; as a result, plants accumulated three catechin compounds: (+)-catechin, epicatechin and epigallocatechin. Not only was the mass of E. grisescens larvae fed on plants previously infested with E. grisescens or treated with WOS significantly lower than that of larvae fed on controls, but also artificial diet supplemented with epicatechin, (+)-catechin or epigallocatechin gallate reduced larval growth rates. In addition, the exogenous application of jasmonic acid, ethylene or auxin induced the biosynthesis of the three catechins, which, in turn, enhanced the resistance of tea plants to E. grisescens, leading to the coordination of the three signalling pathways. Our results suggest that the three catechins play an important role in the defences of tea plants against E. grisescens.

Genome-Wide Identification of the Tify Gene Family and Their Expression Profiles in Response to Biotic and Abiotic Stresses in Tea Plants (Camellia sinensis).

The TIFY family is a plant-specific gene family that is involved in regulating a variety of plant processes, including developmental and defense responses. The chromosome-level genome of the tea plant (Camellia sinensis) has recently been released, but a comprehensive view of the TIFY family in C. sinensis (the CsTIFY genes) is lacking. The current study performed an extensive genome-wide identification of CsTIFY genes. The phylogenetics, chromosome location, exon/intron structure, and conserved domains of these genes were analyzed to characterize the members of the CsTIFY family. The expression profiles of the CsTIFY genes in four organs were analyzed, and they showed different spatial expression patterns. All CsJAZ genes were observed to be induced by jasmonate acid (JA) and exhibited different responses to abiotic and biotic stresses. Six of seven CsJAZ genes (CsJAZ1, CsJAZ2, CsJAZ3, CsJAZ4, CsJAZ7, and CsJAZ8) were upregulated by mechanical wounding and infestation with the tea geometrid (Ectropis obliqua), while infection with tea anthracnose (Colletotrichum camelliae) primarily upregulated the expression levels of CsJAZ1 and CsJAZ10. In addition, CsJAZs were observed to interact with CsMYC2 and AtMYC2. Therefore, the results of this study may contribute to the functional characterization of the CsTIFY genes, especially the members of the JAZ subfamily, as regulators of the JA-mediated defense response in tea plant.

JA-Ile-macrolactone 5b Induces Tea Plant (Camellia sinensis) Resistance to Both Herbivore Ectropis obliqua and Pathogen Colletotrichum camelliae.

Jasmonates (JAs), the group of lipid-derived hormones, were found to control the defense responses in a myriad of plants. Meaningfully, the macrolactones of 12-hydroxy jasmonate isoleucine (12OH-JA-Ile) were reported to induce the defensive response of wild tobacco. However, little to nothing has been known about the elicitation effect of JA-Ile-macrolactones on woody plants to harmful organisms, let alone its underlying mechanisms. Here, we first optimized the synthetic routine using mild toxic reagent isobutyl chloroformate instead of ethyl chloroformate for conjugation, and we used acetonitrile (MeCN) instead of ethyl alcohol for the better dissolution of p-toluenesulfonic acid (p-TsOH) to gain JA-Ile-macrolactones. JA-Ile-macrolactone 5b-treated tea plants significantly inhibited the larvae weight gain of Ectropis obliqua larvae and the lesions caused by Colletotrichum camelliae. Furthermore, the expression level of CsOPR3 was significantly upregulated in 5b-treated leaves. Meanwhile, 5b reduced the accumulation of eriodictyol 7-O-glucuronide (EDG) in tea plants, which was confirmed to promote the growth rate of E. obliqua larvae by artificial diet assay. In conclusion, our study proved that the exogenous application of 5b could induce the tea plant resistance both to herbivore E. obliqua and pathogen C. camelliae, and EDG was identified as one of the secondary metabolites that could influence the growth rate of E. obliqua, but it did not directly influence the infection of C. camelliae in vitro. Further research should be carried out to clarify the mechanism through which 5b induces tea plant resistance to C. camelliae.

The Jasmonic Acid Pathway Positively Regulates the Polyphenol Oxidase-Based Defense against Tea Geometrid Caterpillars in the Tea Plant (Camellia sinensis).

Polyphenol oxidases (PPOs) as inducible defense proteins, contribute to tea (Camellia sinensis) resistance against tea geometrid larvae (Ectropis grisescens), and this resistance has been associated with the jasmonic acid (JA) signaling by testing geometrid performance in our previous work. However, the regulation of PPO-based defense by JA and other hormone signaling underlying these defense responses is poorly understood. Here, we investigated the role of phytohormones in regulating the PPO response to tea geometrids. We profiled levels of defense hormones, PPO activity and CsPPO genes in leaves infested with tea geometrids. Then, hormone levels were manipulated by exogenous application of methyl jasmonate (MeJA), gibberellin acid (GA3), abscisic acid (ABA), JA biosynthesis inhibitors (sodium diethyldithiocarbamate trihydrate, DIECA and salicylhydroxamic acid, SHAM) and GA inhibitor (uniconazole, UNI). Upon geometrid attack, JA levels significantly increased, whereas GA levels notably decreased and ABA level was slightly decreased. And the PPO activity significantly increased in line with the transcript levels of CsPPO2 and CsPPO4 but not CsPPO1. There were an obvious antagonistic cross-talk between JA and GA signals and an association among JA signals, PPO response and herbivore resistance in tea plants. Pretreatment with MeJA increased PPO activity by activating the transcripts of CsPPO2 and CsPPO4, whereas application of JA inhibitor DIECA suppressed PPO activity. GA3 strongly enhanced PPO activity, but ABA did not alter PPO activity. These findings strongly suggest that JA is a central player in PPO-mediated tea resistance against tea geometrids in a manner that prioritizes defense over growth.

Diversity-Oriented Synthesis of Natural-Product-like Libraries Containing a 3-Methylbenzofuran Moiety for the Discovery of New Chemical Elicitors.

Natural products are a major source of biological molecules. The 3-methylfuran scaffold is found in a variety of plant secondary metabolite chemical elicitors that confer host-plant resistance against insect pests. Herein, the diversity-oriented synthesis of a natural-product-like library is reported, in which the 3-methylfuran core is fused in an angular attachment to six common natural product scaffolds-coumarin, chalcone, flavone, flavonol, isoflavone and isoquinolinone. The structural diversity of this library is assessed computationally using cheminformatic analysis. Phenotypic high-throughput screening of ß-glucuronidase activity uncovers several hits. Further in vivo screening confirms that these hits can induce resistance in rice to nymphs of the brown planthopper Nilaparvata lugens. This work validates the combination of diversity-oriented synthesis and high-throughput screening of ß-glucuronidase activity as a strategy for discovering new chemical elicitors.