De novo transcriptome analysis revealed genes involved in flavonoid biosynthesis, transport and regulation in Ginkgo biloba

Ginkgo biloba breeding commonly concentrates on the selection of superior trees that have high flavonoid contents. The flavonoids present in Ginkgo leaves have strong medicinal implications, including anti-dengue, anti-HIV, anticancer, antioxidant and anti-inflammatory properties. Flavonoids play important roles in plant immune responses; however, the molecular mechanisms underlying these interesting responses remain unclear. To obtain a comprehensive understanding, we performed the transcriptome sequencing of Ginkgo with different flavonoid contents. Using an Illumina sequencing platform, we obtained approximately 533,952,528 clean reads. After the sequences were filtered and assembled, the transcriptome data generated 37,625 unigenes, of which 21,472 (57.07%) were successfully annotated in five public databases. Among those genes, many candidates were involved in flavonoid biosynthesis, transport and regulation. Expression profiles were generated, and 457 genes were found to be significantly differentially expressed between the Sample_GB_FH1/2/3 (FH) and Sample_GB_FL1/2/3 (FL) libraries; 246 (53.83%) genes were up-regulated, and 211 (46.17%) were down-regulated. These genes included 14 genes that were enriched in flavonoid transport, 1 MYB gene that encoded a putative transcription factor (TF), and 1 dihydroflavonol reductase (DFR) gene that was involved in the flavonoid pathway. Our results provide comprehensive gene expression information about the Ginkgo transcriptome and can facilitate our understanding of the molecular mechanisms of flavonoid development in Ginkgo. Furthermore, our results markedly expand both the available Ginkgo genetic library and analyses of the species and provide valuable information to the Ginkgo-related pharmaceutical industry.