title: De novo assembly and transcriptome characterization: novel insights into catechins biosynthesis in Camellia sinensis.
abstract: BACKGROUND
  Tea is a popular natural non-alcoholic beverage consumed worldwide due to its bioactive ingredients, particularly catechins (flavan-3-ols). Catechins not only contribute to tea quality but also serve important functions in the anti-stress regulation of secondary metabolic pathways. However, the percentages of various catechins are different among tea plant [Camellia sinensis (L.) O. Kuntze] cultivars. This study aimed to elucidate the biosynthetic mechanism of catechins. Transcriptomes from leaf tissues of four tea plant cultivars, 'Yunnanshilixiang', 'Chawansanhao', 'Ruchengmaoyecha', and 'Anjibaicha', were sequenced using the high-throughput sequencing platform Illumina HiSeq™ 2000. De novo assemble were also performed. Catechins contents were measured through reversed-phase high-performance liquid chromatography (RP-HPLC), and the biosynthetic pathway was also surveyed.
  
  
  RESULTS
  We constructed a unified unigene database. A total of 146,342 pairs of putative orthologs from the four tea plant cultivars, 'Yunnanshilixiang', 'Chawansanhao', 'Ruchengmaoyecha', and 'Anjibaicha' were generated. Approximately 68,890 unigenes (47.1%) were aligned to the sequences of seven public databases with a cut-off E-value of 1E-5. A total of 217 differentially expressed genes were found through RPKM values, and 150 unigenes were assigned to the flavonoid biosynthetic pathway using the integrated function annotation. The (-)-EGC and (-)-EC contents were significantly lower and the (+)-GC and (+)-C contents were abnormally higher in 'Ruchengmaoyecha' than in 'Yunnanshilixiang', 'Chawansanhao', and 'Anjibaicha'. The proportion of catechins was confirmed by selecting critical genes (ANS, ANR, and LAR) for qRT-PCR analysis.
  
  
  CONCLUSIONS
  This study provided a global survey of transcriptomes from four tea plant cultivars and serves as an available resource of genetic diversity. The analyses of transcriptome profiles and physiological indicators not only identified the putative genes involved in the flavonoid biosynthetic pathway but also provided some novel insights for the mechanisms of catechins biosynthesis.
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Wu
authors.forename: Xing-Hui
authors.initials: XH
authors.lastname: Li
authors.forename: Zhi-Wei
authors.initials: ZW
authors.lastname: Liu
authors.forename: Zhi-Sheng
authors.initials: ZS
authors.lastname: Xu
authors.affiliation: Tea Science Research Institute, College of Horticulture, Nanjing Agricultural University, Nanjing 210095, China. zhuangjing@njau.edu.cn.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhuang
mesh_terms: D001482:Base Composition / Q000235:genetics; D028241:Camellia sinensis / Q000235:genetics* / Q000378:metabolism*; D002392:Catechin / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D020133:Reverse Transcriptase Polymerase Chain Reaction; D059467:Transcriptome / Q000235:genetics
chemical_list: D002392:Catechin