A candidate gene identified in converting platycoside E to platycodin D from Platycodon grandiflorus by transcriptome and main metabolites analysis

Abstract

Platycodin D and platycoside E are two triterpenoid saponins in Platycodon grandiflorus, differing only by two glycosyl groups structurally. Studies have shown β-Glucosidase from bacteria can convert platycoside E to platycodin D, indicating the potential existence of similar enzymes in P. grandiflorus. An L9(34) orthogonal experiment was performed to establish a protocol for calli induction as follows: the optimal explant is stems with nodes and the optimum medium formula is MS + NAA 1.0 mg/L + 6-BA 0.5 mg/L to obtain callus for experimental use. The platycodin D, platycoside E and total polysaccharides content between callus and plant organs varied wildly. Platycodin D and total polysaccharide content of calli was found higher than that of leaves. While, platycoside E and total polysaccharide content of calli was found lower than that of leaves. Associating platycodin D and platycoside E content with the expression level of genes involved in triterpenoid saponin biosynthesis between calli and leaves, three contigs were screened as putative sequences of β-Glucosidase gene converting platycoside E to platycodin D. Besides, we inferred that some transcription factors can regulate the expression of key enzymes involved in triterpernoid saponins and polysaccharides biosynthesis pathway of P. grandiflorus. Totally, a candidate gene encoding enzyme involved in converting platycoside E to platycodin D, and putative genes involved in polysaccharide synthesis in P. grandiflorus had been identified. This study will help uncover the molecular mechanism of triterpenoid saponins biosynthesis in P. grandiflorus.

Molecular Cloning and Functional Characterization of a β-Glucosidase Gene to Produce Platycodin D in Platycodon grandiflorus

“…We previously obtained three candidate genes (CL4020.Contig1_ All, Unigene 1627_All, and Unigene7900_All; Su et al, 2021).…”

“…Studies have shown that the content of PE is higher in the leaves of P. grandiflorus than in other parts (Su et al, 2021;Yu et al, 2021). Therefore, we collected P. grandiflorus leaves at seven time points of the day and night from 6:00 am to 12:00 pm (at 3-h intervals) as samples for analysis.…”

“…The enzymatic biotransformation of PE to PD in vitro has been demonstrated in various studies using β-galactosidase from Aspergillus oryzae ( Ha et al, 2010 ), snailase ( Li et al, 2012b ), laminarinase ( Jeong et al, 2014 ), β-glucosidase from Aspergillus usamii ( Ahn et al, 2018 ), recombinant β-glucosidases from Caldicellulosiruptor bescii ( Kil et al, 2019 ), and cytolase ( Shin et al, 2020 ). We further speculated that there might be a deglycosylase in P. grandiflorus , which could also catalyze the conversion of PE into PD ( Su et al, 2021 ). Although great progress has been made in the study of how enzymes catalyzed the conversion of PE to PD, little is known about the β-glucosidase gene with this function in P. grandiflorus .…”

“…Leaves of P. grandiflorus are rich in PE, which were discarded when collecting medicinal plants. ( Shin et al, 2019 ; Su et al, 2021 ; Yu et al, 2021 ). Reducing the PE content-a lot of which is wasted a lot in actual production-may increase the PD content of P. grandiflorus plants.…”

Characterization of Saponins from Various Parts of Platycodon grandiflorum Using UPLC-QToF/MS

“…Therefore, in this study, using UPLC combined with QTOF-mass spectrometry analysis, 38 saponins were identified or tentatively characterized with four different parts, including the blanching process. Thus, considering the change in saponin content in these materials, along with the transformation in their structure, platycodin (major saponin in PG) pathways are examined in light of previous studies [ 37 , 38 , 39 , 40 ].…”