Transcriptome Sequencing Of Solanum Nigrum Linn Fruits Reveals The Genes Related To The Accumulation Of Flavonoids

Solanum nigrum Linn.(S.nigrum),an annual herbal plant of Solanaceae family,has been known as a traditional herb medicine in China because of its antiperiodic,antitussive,antiphlogistic,diuretic,emollient,febrifuge,purgative and sedative effects.The fruits of S.nigrum is rich in flavonoid compounds,and there are some differences in the content of flavonoids between unripe fruits and ripe fruits.Owing to the lack of genomic information of S.nigrum,the mechanism of flavonoid biosynthesis in S.nigrum is still unclear.In this work,we comprehensively compared the transcriptome profiles of ripe fruits(RFs)and unripe fruits(UFs)and identified the genes related to flavonoid biosynthesis in S.nigrum.Total RNA was isolated from RFs and UFs,and then,mRNA was separated and purificated from total RNA to condtructed cDNA libraries.And then,cDNA libraries were sequenced with Next Generation Sequencing(NGS)technology.In total,118198 unigenes with a N50 length of 1339 bp were de novo assembled.Among the assembled sequences,we annotated 70116 unigenes(59.3% of the total unigenes)against at least one of the databases.The thresholds of false discovery rate(FDR)< 0.001 and log-fold expression change(log FC)> 2 or <-2 were used to select the differential expression genes(DEGs)in RF and UF of S.nigrum.Eventually we identified 527 genes that were differential expression in RFs and UFs,including 329 down-regulated genes and 198 up-regulated genes.Especially,8 DEGs were identified to be involved in flavonoid biosynthesis.And most of the 8 flavonoid-related genes were highly expressed in RFs.Finally,we found that the differential expression of three genes that were related to the synthesis of dihydroflavonol-4-reductase(DFR),flavonoid 3’,5’-hydroxylase(F3’5’H)and anthocyanin synthase(ANS)was the key reason contribute to differences in flavonoid biosynthesis between RFs and UFs of S.nigrum.This study provide some important information for the flavonoid accumulation in S.nigrum and improve our understanding of the molecular mechanisms of flavonoid biosynthesis in S.nigrum.To further validate the reliability of the RNA-seq data from our differentially expression analysis,five unigenes involved in flavonoid biosynthesis were randomly selected and examined by qRT-PCR.We found that the relative expression level obtained by qRT-PCR were consistent with that by sequencing.Therefore,the transcriptomic analysis was highly reproducible and reliable for additional investigations of key genes involved in flavonoid accumulations in S.nigrum.