Global Transcriptional Analysis Reveals the Complex Relationship between Tea Quality, Leaf Senescence and the Responses to Cold-Drought Combined Stress in Camellia sinensis

Abstract

In field conditions, especially in arid and semi-arid areas, tea plants are often simultaneously exposed to various abiotic stresses such as cold and drought, which have profound effects on leaf senescence process and tea quality. However, most studies of gene expression in stress responses focus on a single inciting agent, and the confounding effect of multiple stresses on crop quality and leaf senescence remain unearthed. Here, global transcriptome profiles of tea leaves under separately cold and drought stress were compared with their combination using RNA-Seq technology. This revealed that tea plants shared a large overlap in unigenes displayed “similar” (26%) expression pattern and avoid antagonistic responses (lowest level of “prioritized” mode: 0%) to exhibit very congruent responses to co-occurring cold and drought stress; 31.5% differential expressed genes and 38% of the transcriptome changes in response to combined stresses were unpredictable from cold or drought single-case studies. We also identified 319 candidate genes for enhancing plant resistance to combined stress. We then investigated the combined effect of cold and drought on tea quality and leaf senescence. Our results showed that drought-induced leaf senescence were severely delayed by (i) modulation of a number of senescence-associated genes and cold responsive genes, (ii) enhancement of antioxidant capacity, (iii) attenuation of lipid degradation, (iv) maintenance of cell wall and photosynthetic system, (v) alteration of senescence-induced sugar effect/sensitivity, as well as (vi) regulation of secondary metabolism pathways that significantly influence the quality of tea during combined stress. Therefore, care should be taken when utilizing a set of stresses to try and maximize leaf longevity and tea quality.

Comprehensive profiling of alternative splicing landscape during cold acclimation in tea plant

“…In tea plant, previous studies indicate AS is involved in important secondary metabolism pathways such as flavonoid and linalool biosynthesis [29,34]. Cold stress is one of the most severe abiotic stresses in tea plant, and a series of studies have been focusing on tea plant gene regulation during cold stress and cold acclimation [27,35,36]. Through cold acclimation, tea plants can alleviate the harm of low temperature and enhance their tolerance to cold stress [26].…”

Exogenous abscisic acid induces on lipid and flavonoid metabolism of tea plant under drought stress

“…Previous study in tea plants showed that the expressions of the genes related to starch synthesis (AGPase, SS) were inhibited and the expressions of the genes related to starch degradation (AMY, BAM) were induced, whereas the expressions of the genes related to sucrose synthesis (UDPGase, SPS) and degradation (INVs) were highly induced under drought stress. [1,2]. However, in tea plants, the effect of exogenous ABA on genes involved in starch and sucrose metabolism was rarely reported.…”

“…Leaf chlorophyll was extracted with ethanol according to previous studies [39]. Third leaf was sampled to measure maximum quantum yield of PSII according to previous studies [1]. The contents of malondialdehyde (MDA) in the leaves were measured by the thiobarbituric acid (TBA) method according to previous studies [12].…”

“…in response to drought stress were mainly enriched in volatile compounds, flavonoids, theanine biosynthesis pathways, and some DEGs were also involved in leaf senescence, such as LOX (lipoxygenase), BGLU6/14/18/41/42 (beta-glucosidases 6/14/18/41/42), BSMT (salicylate/benzoate carboxyl methyltransferase), ADC (arginine decarboxylase), GS (glutamine synthetase), GLS (glutaminase), CHI (chalcone isomerase), F3′5′H (flavonoid 3′,5′-hydroxylase), FLS (flavonol synthase), F3H (flavanone 3-hydroxylase) [1]. Another study in our lab showed that a large numbers of the differentially expressed proteins in response to drought stress were mainly involved in glycolysis/gluconeogenesis, starch and sucrose synthesis, or degradation metabolism, and second metabolism [6].…”

“…In the study, we analyzed the effects of exogenous ABA on genes and metabolites related to flavonoid metabolism of tea leaves under drought stress using transcriptome and metabolomics.Previous researches on tea plants showed that the expressions of the genes related to flavonoid biosynthesis were firstly decreased and subsequently increased in response to drought stress, such as CHS, DFR, LAR and ANR, and the expressions of FLS and FNS were continuously upregulated in response to drought stress[3]. The expressions of the genes related to flavonoid biosynthesis, such as PAL, C4H, 4CL, CHS and DFR, were significantly induced by drought[1].However, in tea plants, the effect of exogenous ABA on genes related to flavonoids biosynthetic in response to drought stress was rarely reported. In the present study, transcriptome analysis revealed that the exogenous ABA significantly induced the expressions of genes related to flavonoid biosynthesis of tea leaves under drought stress.…”