Full-Length Transcriptome Analyses of Genes Involved in Triterpenoid Saponin Biosynthesis of Psammosilene tunicoides Hairy Root Cultures With Exogenous Salicylic Acid

Abstract

Triterpenoid saponins constitute a diverse class of bioactive compounds in medicinal plants. Salicylic acid (SA) is an efficient elicitor for secondary metabolite production, but a transcriptome-wide regulatory network of SA-promoted triterpenoid saponin biosynthesis remains little understood. In the current study, we described the establishment of the hairy root culture system for Psammosilene tunicoides, a triterpenoid saponin-producing medicinal herb in China, using genetic transformation by Agrobacterium rhizogenes. Compared to controls, we found that total saponin content was dramatically increased (up to 2.49-fold) by the addition of 5 mg/L SA in hairy roots for 1 day. A combination of single-molecule real-time (SMRT) and next-generation sequencing (Illumina RNA-seq) was generated to analyze the full-length transcriptome data for P. tunicoides, as well as the transcript profiles in treated (8 and 24 h) and non-treated (0 h) groups with 5 mg/L SA in hairy roots. A total of 430,117 circular consensus sequence (CCS) reads, 16,375 unigenes and 4,678 long non-coding RNAs (lncRNAs) were obtained. The average length of unigenes (2,776 bp) was much higher in full-length transcriptome than that derived from single RNA-seq (1,457 bp). The differentially expressed genes (DEGs) were mainly enriched in the metabolic process. SA up-regulated the unigenes encoding SA-binding proteins and antioxidant enzymes in comparison with controls. Additionally, we identified 89 full-length transcripts encoding enzymes putatively involved in saponin biosynthesis. The candidate transcription factors (WRKY, NAC) and structural genes (AACT, DXS, SE, CYP72A) might be the key regulators in SA-elicited saponin accumulation. Their expression was further validated by quantitative real-time PCR (qRT-PCR). These findings preliminarily elucidate the regulatory mechanisms of SA on triterpenoid saponin biosynthesis in the transcriptomic level, laying a foundation for SA-elicited saponin augmentation in P. tunicoides.

Effect of biotic stress on the presence of secondary metabolites in field pea grains

“…37 The underlying mechanisms of their activity seems to be based on their ability to form complexes with sterols present in the cell membrane and consequently to cause membrane perturbation. 38 As it was reported by Su et al, 39 saponin biosynthesis could be regulated by salicylic acid (SA). Saponin increase in seed, as observed in the present study, could be a consequence of the SA-mediated plant systemic response to pathogen.…”

Enhancement of Phytosterol and Triterpenoid Production in Plant Hairy Root Cultures—Simultaneous Stimulation or Competition?

“…Jasmonic acid and its methyl ester (MeJA) are the most commonly applied elicitors in plant in vitro cultures, including adventitious and hairy roots of many plant species, and their efficiency was reported in numerous studies on various compounds [ 60 , 61 , 80 , 81 ]. Another plant hormone often applied as a potent elicitor of triterpenoid saponin biosynthesis is salicylic acid (SA) [ 82 ]. In contrast, some reports revealed fungi-derived biotic elicitors seem to act on triterpenoid biosynthesis inversely to jasmonates or salicylic acid [ 61 , 83 ].…”

Natural products of pentacyclic triterpenoids: from discovery to heterologous biosynthesis

“…SE , as one of the key enzymes in the biosynthetic pathway of triterpene saponins, catalyzes the epoxidation of SQ by inserting an oxygen source between CC to generate 2,3-oxidosqualene. 156 Su et al 225 found that the total saponin content dramatically increased (up to 2.49-fold) with the addition of 5 mg L −1 SA in hairy roots for 1 day compared to the control. Furthermore, MeJA 226 and fungal elicitor 227 could regulate the expression of the SE gene, thereby influencing the biosynthesis of triterpene saponins.…”