Transcriptomic Analysis Reveals the Molecular Mechanisms of Drought-Stress-Induced Decreases in Camellia sinensis Leaf Quality

Abstract

The tea plant [Camellia sinensis (L.) O. Kuntze] is an important commercial crop rich in bioactive ingredients, especially catechins, caffeine, theanine and other free amino acids, which the quality of tea leaves depends on. Drought is the most important environmental stress affecting the yield and quality of this plant. In this study, the effects of drought stress on the phenotype, physiological characteristics and major bioactive ingredients accumulation of C. sinensis leaves were examined, and the results indicated that drought stress resulted in dehydration and wilt of the leaves, and significant decrease in the total polyphenols and free amino acids and increase in the total flavonoids. In addition, HPLC analysis showed that the catechins, caffeine, theanine and some free amino acids in C. sinensis leaves were significantly reduced in response to drought stress, implying that drought stress severely decreased the quality of C. sinensis leaves. Furthermore, differentially expressed genes (DEGs) related to amino acid metabolism and secondary metabolism were identified and quantified in C. sinensis leaves under drought stress using high-throughput Illumina RNA-Seq technology, especially the key regulatory genes of the catechins, caffeine, and theanine biosynthesis pathways. The expression levels of key regulatory genes were consistent with the results from the HPLC analysis, which indicate a potential molecular mechanism for the above results. Taken together, these data provide further insights into the mechanisms underlying the change in the quality of C. sinensis leaves under environmental stress, which involve changes in the accumulation of major bioactive ingredients, especially catechins, caffeine, theanine and other free amino acids.

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

“…The modes of physiological and molecular responses to drought have been demonstrated in tea plants (Liu et al, 2015, 2016; Wang et al, 2016). However, those stressors might co-occur in the field, and cause leaf senescence as well as quality degradation; thus, marker-assisted breeding or cross-breeding, which targets single cold or drought stress, might be insufficient for improving the performance of tea plants in the field.…”

“…Every year, substantial loss of tea production and degradation of tea quality due to leaf senescence can result from a particular or often a combination of different stress conditions (Liu et al, 2015; Wang et al, 2016). In field conditions, cold stress often occurs in conjunction with drought stress, and this combination has been recognized as realistic threats faced by plants in the winter of semi-arid or drought-stricken areas (Su et al, 2015).…”

“…These findings support the role of the antioxidant mechanisms to be an essential strategy to guard plants against stress combinations (Pandey et al, 2015). Although cold and drought stress have been extensively studied in tea plants, little is known about how their combination impacts plants on a whole-genome basis (Wang et al, 2013, 2016; Zheng et al, 2015; Liu et al, 2016). In recent years, stress-induced premature senescence has become a major threat to crop yield worldwide and considered an important field of research (Schippers et al, 2015).…”

“…If one considers the economic implications of tea, it is not surprising that the metabolic pathways and enzymes involved in the formation of tea flavonoids, theanine, and volatile compounds have attracted the attention of many researchers. Recently, (Li et al, 2015) analyzed the gene expression profiles of 13 different tissue samples from various organs and developmental stages, which further elucidated the gene network responsible for the regulation of flavonoid, caffeine and theanine biosynthetic pathways in tea plants; (Wang et al, 2016) analyzed secondary metabolism changes in tea leaves during short-term drought stress using RNA-Seq technology. They revealed drought stress resulted in a significant increase in the total flavonoids and a decrease in the free amino acids and total polyphenols.…”

Gene expression analysis of bud and leaf color in tea

“…Recently, RNA-Seq method of high-throughput sequencing technology has been widely used to explore the potential mechanisms associated with important traits in C. sinensis (Paul et al, 2014;Li et al, 2015;Shi et al, 2015;Tai et al, 2015;Wei et al, 2015;Wang et al, 2016;Wu et al, 2016;Zhang et al, 2016). This method allows a comparison of the whole transcriptome of samples with large difference in certain trait or under treatments.…”