Identification of putative flavonoid-biosynthetic genes through transcriptome analysis of Taihe Toona sinensis bud

Toona sinensis, a member of Meliaceae family, is a traditional Chinese woody vegetable widely used as food and in health since ancient times. T. sinensis bud has extensive clinical uses because of its high flavonoid content. However, the literature lacks information on flavonoid metabolism and characterization of the corresponding genes in T. sinensis. In this study, we constructed two cDNA libraries of green (GYC-2) and purple toons (BYC2) distributed in Taihe County of Anhui Province in China. A total of 9.48 Gb of raw sequencing reads were generated using Illumina technology. Obtained raw reads were assembled into 66,331 non-redundant unigenes with mean length 1076 bp. A total of 50,582 unigenes (accounting for 76. 26% of all-unigenes) could be matched to public database using BLASTx. Through alignment against KEGG database, a total of 34,183 were annotated into 135 KEGG pathways. Among such pathways, many candidate genes that are associated with flavonoid biosynthesis were discovered in our transcriptome data. In total, 9541 unigenes identified were differentially expressed genes (DEGs), including 5408 up-regulated unigenes and 4133 down-regulated unigenes in green toon vs purple toon. Moreover, numerous transcription factors (MYB, bHLH, and WD40) were found in our data. Many genes related to flavonoid biosynthesis showed preferential expression in BYC-2 cultivar. Therefore, de novo transcriptome analysis of unique transcripts provides an invaluable resource for exploring vital gene related to flavonoid biosynthesis of T. sinensis bud.