Abstract
Characteristic secondary metabolites, including flavonoids, theanine and caffeine, are important components of Camellia sinensis, and their biosynthesis has attracted widespread interest. Previous studies on the biosynthesis of these major secondary metabolites using next-generation sequencing technologies limited the accurately prediction of full-length (FL) splice isoforms. Herein, we applied single-molecule sequencing to pooled tea plant tissues, to provide a more complete transcriptome of C. sinensis. Moreover, we identified 94 FL transcripts and four alternative splicing events for enzyme-coding genes involved in the biosynthesis of flavonoids, theanine and caffeine. According to the comparison between long-read isoforms and assemble transcripts, we improved the quality and accuracy of genes sequenced by short-read next-generation sequencing technology. The resulting FL transcripts, together with the improved assembled transcripts and identified alternative splicing events, enhance our understanding of genes involved in the biosynthesis of characteristic secondary metabolites in C. sinensis.
Highlights
The tea plant (Camellia sinensis) is an important horticultural crop and source of one of the most popular natural non-alcoholic beverages consumed across the world (Chen et al, 2007; Zhang et al, 2015)
Most C. sinensis transcript studies have been based on next-generation sequencing (Wu et al, 2014; Zhang et al, 2015), and the short reads resulting from this approach have prevented the accurate assembly of FL transcripts in the absence of genomic sequence information (Au et al, 2013)
Our results demonstrated that single-molecule sequencing (SMS) sequencing is highly powerful in alternative splicing event discovery and provides a rich data resource for later functional studies of different isoforms in C. sinensis
Summary
The tea plant (Camellia sinensis) is an important horticultural crop and source of one of the most popular natural non-alcoholic beverages consumed across the world (Chen et al, 2007; Zhang et al, 2015). The rich flavors of tea are mainly attributable to the characteristic secondary metabolites including flavonoids, theanine and caffeine (Liang et al, 2001; Mamati et al, 2006). These secondary compounds have been confirmed to be beneficial to human health (Hertog et al, 1993; Cabrera et al, 2006; Khan and Mukhtar, 2007) and contribute to the nutrient content and unique taste of tea (Chu and Juneja, 1997; Chen et al, 2008). Theanine is synthesized from glutamic acid and ethylamine by theanine synthetase (TS) in the roots of the tea plant (Deng et al, 2012).
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