CsHCT-Mediated Lignin Synthesis Pathway Involved in the Response of Tea Plants to Biotic and Abiotic Stresses

Abstract

Many studies have shown that phenolic compounds such as lignin and flavonoids enhance plant resistance. Tea plants are rich in flavonoid compounds. Whether these compounds are related to tea plant resistance is unclear. In this study, an interesting conclusion was drawn on the basis of experimental results: in response to abiotic stress (except for sucrose treatment), gene expression was increased in the phenylpropanoid and lignin pathways and was reduced in the flavonoid pathway in tea plants. CsHCTs, the genes located at the branch point of the lignin and flavonoid pathways, are most suitable for regulating the ratio of carbon flow in the lignin pathway and flavonoid synthesis. Enzymatic and genetic modification experiments proved that CsHCTs encode hydroxycinnamoyl-coenzyme A:shikimate/quinate hydroxycinnamoyl transferase in vitro and in vivo. Furthermore, the genetic modification results showed that the contents of phenolic acids and lignin were increased in tobacco and Arabidopsis plants overexpressing CsHCTs, whereas the content of flavonol glycosides was decreased. Both types of transgenic plants showed resistance to many abiotic stresses and bacterial infections. We speculate that CsHCTs participate in regulation of the metabolic flow of carbon from the flavonoid pathway to the chlorogenic acid, caffeoylshikimic acid, and lignin pathways to increase resistance to biotic and abiotic stresses.

Integrated metabolomic and transcriptomic analysis reveals the role of phenylpropanoid biosynthesis pathway in tomato roots during salt stress

“…It also has a physiological modulating effect, not only inhibiting free radical-producing enzymes but also increasing the activity of free radical-eliminating enzymes ( Mathew and Abraham, 2004 ; Berton et al., 2020 ). Lignin is the second most abundant secondary metabolite in nature following cellulose and important structural material in plant cell wall formation, which has important biological functions for the plant body and can improve plant resistance against biotic and abiotic stresses ( Chen et al., 2021 ). Enhancing salt tolerance to resist damage incurred by salt stress by increasing lignin content has been demonstrated in transgenic Arabidopsis thaliana ( Duan et al., 2020 ), apple ( Malus × domestica ) ( Chen et al., 2019 ; Chen et al., 2020 ), sweet potato ( Ipomoea batatas ) calli ( Park et al., 2011 ), and Chinese cabbage ( Brassica rapa ) ( Cao et al., 2020 ).…”

Transcriptional Analysis of Tea Plants (Camellia sinensis) in Response to Salicylic Acid Treatment

“…Exogenous SA treatment promoted the expression of genes in the lignin pathway, indicating that the lignin pathway can actively respond to SA signals and participate in SA-mediated resistance to adversity. CsHCTs were proposed to be involved in regulating the metabolic flow of carbon from the flavonoid pathway to chlorogenic acid and lignin pathways . In our study, the transcription level of CsHCT1 was also positively correlated to SA.…”

“…CsHCTs were proposed to be involved in regulating the metabolic flow of carbon from the flavonoid pathway to chlorogenic acid and lignin pathways. 27 In our study, the transcription level of CsHCT1 was also positively correlated to SA. CADs, as one kind of dehydrogenase specifically involved in the last step of monolignol synthesis, were the most upregulated genes (CsCAD1) after SA treatment.…”

“…25,26 The accumulation of lignin in tea plants often changes with the occurrence of biological stress. 27 The ability of tea tree to resist pests and diseases depends on the rich natural polyphenols on the one hand, and, on the other hand, plant hormones such as SA and methyl jasmonate (MeJA) also play a vital role in the process of resisting pathogenic bacteria. Tea green leafhopper (Empoasca onukii Matsuda) attack can trigger a significant increase in SA and a minor increase in jasmonic acid (JA) in the infested tea leaves.…”

“…Tea [Camellia sinensis (L.) O. Kuntze] is an important leaf-consumed economic plant in China; healthy leaves have significant impacts on the quality of tea beverages. Tea leaves are rich in polyphenols, caffeine, theanine, and other secondary metabolites, which confer teas with rich taste, pleasant flavors, and multiple health benefits. − The diverse flavonoid derivatives in tea plants, such as catechins, anthocyanins, and proanthocyanidins (PAs), also appear to function in resistance against various biotic and abiotic stresses, such as low temperature, UV irradiation, and fungal infection. , When tea trees suffered from extreme temperatures or UV-B irradiation, the increased accumulation of anthocyanins is one of the most common phenotypic traits. , The accumulation of lignin in tea plants often changes with the occurrence of biological stress . The ability of tea tree to resist pests and diseases depends on the rich natural polyphenols on the one hand, and, on the other hand, plant hormones such as SA and methyl jasmonate (MeJA) also play a vital role in the process of resisting pathogenic bacteria.…”