Transcriptome analysis of main roots of Panax notoginseng identifies genes involved in saponin biosynthesis under arsenic stress

Abstract

Saponin is the key medicinal composition of P. notoginseng, which is one of the important traditional herbal medicines in the genus of Panax in China. The underlying genetic basis of saponin regulation under arsenic stress is not elucidated. The contents of saponin (R1, Rg1, Rb1), relative key enzyme squalene synthase (SS) in main roots of P. notoginseng under different arsenic treatment concentration (As5+: 0, 20, 140 mg kg−1) were determined at early flowering stage. Meanwhile, candidate genes involved in saponin metabolism were identified based on the transcriptomes of P. notoginseng roots compared using RNA sequencing (RNA-seq). The results showed that saponin (R1, Rg1, Rb1) contents and saponin yield in main roots increased and SS activities did not changed significantly with increased arsenic concentrations. Genes involved with environmental information processing were differentially regulated in response to arsenic treatment. Metabolism processing associated with saponin biosynthesis was the first time that expression of the saponin biosynthetic genes was monitored in response to arsenic. Expression patterns of genes of key enzymes relating to the pathways of saponin biosynthesis were identified, including genes: CYP71D444 and CYP73A100 for conversion from protopanaxadiol to protopanaxatriol, UGTPg25 for glycosylation and PnSE2 for oxidosqualene. The results indicate that expression patterns of arsenic-regulated transcript in P. notoginseng would be instrumented in revealing the genetic networks that govern saponin biosynthesis under arsenic stress. Main findingsGenes of key enzymes relating to the pathways of saponin (relative genes: CYP71D444, CYP73A100, PnSE2) biosynthesis were identified.