Defensive Responses of Tea Plants (Camellia sinensis) Against Tea Green Leafhopper Attack: A Multi-Omics Study

Abstract

Tea green leafhopper [Empoasca (Matsumurasca) onukii Matsuda] is one of the most devastating pests of tea plants (Camellia sinensis), greatly impacting tea yield and quality. A thorough understanding of the interactions between the tea green leafhopper and the tea plant would facilitate a better pest management. To gain more insights into the molecular and biochemical mechanisms behind their interactions, a combined analysis of the global transcriptome and metabolome reconfiguration of the tea plant challenged with tea green leafhoppers was performed for the first time, complemented with phytohormone analysis. Non-targeted metabolomics analysis by ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF MS), together with quantifications by ultra-performance liquid chromatography triple quadrupole mass spectrometry (UPLC-QqQ MS), revealed a marked accumulation of various flavonoid compounds and glycosidically bound volatiles but a great reduction in the level of amino acids and glutathione upon leaf herbivory. RNA-Seq data analysis showed a clear modulation of processes related to plant defense. Genes pertaining to the biosynthesis of phenylpropanoids and flavonoids, plant-pathogen interactions, and the biosynthesis of cuticle wax were significantly up-regulated. In particular, the transcript level for a CER1 homolog involved in cuticular wax alkane formation was most drastically elevated and an increase in C29 alkane levels in tea leaf waxes was observed. The tea green leafhopper attack triggered a significant increase in salicylic acid (SA) and a minor increase in jasmonic acid (JA) in infested tea leaves. Moreover, transcription factors (TFs) constitute a large portion of differentially expressed genes, with several TFs families likely involved in SA and JA signaling being significantly induced by tea green leafhopper feeding. This study presents a valuable resource for uncovering insect-induced genes and metabolites, which can potentially be used to enhance insect resistance in tea plants.

Keywords: RNA-Seq; defense response; hormone signaling; metabolomics; plant-herbivore interaction; tea green leafhopper.

Figure 1

PCA analysis of tea leaves exposed to tea green leafhopper attack and mechanical damage. (A) PCA score plot for tea samples based on 2,381 molecular features detected in ESI⁺. (B) PCA score plot for tea samples based on 906 molecular features detected in ESI^-. R2X, explained variation. PC1, the first principal component. PC2, the second principal component. For tea samples with different treatments, three biological replicates were prepared, where one replicate was a pool of collected materials from different tea plants. LD, tea green leafhopper-infested leaves; MD, mechanically damaged leaves; CK, undamaged control.

Figure 2

Comparisons of the relative abundance of the identified DEMs among different treatment groups. LD, tea green leafhopper-infested leaves. Kae, kaempferol; MD, mechanically damaged leaves; CK, undamaged control.

Figure 3

Quantitative analysis of the changes of SA (A), JA (B) and ABA (C) contents in tea leaves from different treatment groups. Results are expressed as mean ± standard deviation (n = 3). Different letters indicate significant difference (p < 0.05) according to Tukey's HSD test. LD, tea green leafhopper-infested leaves; MD, mechanically damaged leaves; CK, undamaged control.

Figure 4

Overview of tea leave transcriptome subjected to mechanical damage and tea green leafhopper infestation. (A) PCA score plot based on normalized gene count data from all samples. (B) Venn diagram showing the numbers of common and specific DEGs among different treatment groups. (C) Analysis of KEGG Orthology (KO) pathway enrichment of DEGs between MD and CK. (D) Analysis of KO pathway enrichment of DEGs between LD and CK. (E) Analysis of KO pathway enrichment of DEGs between LD and MD. The x axis in (C), (D), and (E) represents KEGG pathways while the y axis represents the -log10 (p-value). LD, tea green leafhopper-infested leaves; MD, mechanically damaged leaves; CK, undamaged control.

Figure 5

Analysis of abundant very-long-chain fatty acid derivatives in CK and LD leaf waxes. Error bars represent SD (n = 3). Statisical significance of differences between CK and LD means is indicated by *p < 0.05 and **p < 0.01. LD, tea green leafhopper-infested leaves; CK, undamaged control.