Five Pairs of Enantiomer as Rearrangement Products from Secoiridoids in Gentiana macrophylla Pall.

Five racemates (1-5) were isolated from Gentiana macrophylla, in which 2-5 were successfully separated into four pairs of enantiomers (2a and 2b, 3a and 3b, 4a and 4b, and 5a and 5b), whereas the resolution of 1 failed due to the hemiacetal functionality at the stereogenic center. Using electronic circular dichrosim calculation, the relationship of the molecular rotation direction and the carbon R/S chirality was revealed, and each pair of enantiomer was identified as (-)-(S)-gentianmacrol B (2a) and (+)-(R)-gentianmacrol B (2b), (-)-(S)-8-methoxy-gentianol (3a) and (+)-(R)-8-methoxy-gentianol (3b), (+)-(S)-8-methyl-gentianadine (4a) and (-)-(R)-8-methyl-gentianadine (4b), and (-)-(S)-gentianol (5a) and (+)-(R)-gentianol (5b). Besides, these compounds could be divided into two series, 1-2 containing the benzene ring moiety and 3-5 containing the pyridine ring moiety. Considering that their molecular skeleton could not be generated from the classical biosynthesis pathway in plants, the plausible biosynthesis pathways of 1-5 were deduced to be transformed from secoiridoids in G. macrophylla. Due to the significant difference in the pharmacological effect for the optical factor, our research provided new diverse molecules for further optical activity studies in drug research.

Transcriptome and metabolome analysis reveals mechanism of light intensity modulating iridoid biosynthesis in Gentiana macrophylla Pall.

Light intensity is a key factor affecting the synthesis of secondary metabolites in plants. However, the response mechanisms of metabolites and genes in Gentiana macrophylla under different light intensities have not been determined. In the present study, G. macrophylla seedlings were treated with LED light intensities of 15 µmol/m2/s (low light, LL), 90 µmol/m2/s (medium light, ML), and 200 µmol/m2/s (high light, HL), and leaves were collected on the 5th day for further investigation. A total of 2162 metabolites were detected, in which, the most abundant metabolites were identified as flavonoids, carbohydrates, terpenoids and amino acids. A total of 3313 and 613 differentially expressed genes (DEGs) were identified in the LL and HL groups compared with the ML group, respectively, mainly enriched in KEGG pathways such as carotenoid biosynthesis, carbon metabolism, glycolysis/gluconeogenesis, amino acids biosynthesis, plant MAPK pathway and plant hormone signaling. Besides, the transcription factors of GmMYB5 and GmbHLH20 were determined to be significantly correlated with loganic acid biosynthesis; the expression of photosystem-related enzyme genes was altered under different light intensities, regulating the expression of enzyme genes involved in the carotenoid, chlorophyll, glycolysis and amino acids pathway, then affecting their metabolic biosynthesis. As a result, low light inhibited photosynthesis, delayed glycolysis, thus, increased certain amino acids and decreased loganic acid production, while high light got an opposite trend. Our research contributed significantly to understand the molecular mechanism of light intensity in controlling metabolic accumulation in G. macrophylla.

Genomic characterization of WRKY transcription factors related to secoiridoid biosynthesis in Gentiana macrophylla.

Gentiana macrophylla is one of Chinese herbal medicines in which 4 kinds of iridoids or secoiridoids, such as loganic acid, sweroside, swertiamarin, and gentiopicroside, are identified as the dominant medicinal secondary metabolites. WRKY, as a large family of transcription factors (TFs), plays an important role in the synthesis of secondary metabolites in plants. Therefore, WRKY genes involved in the biosynthesis of secoiridoids in G. macrophylla were systematically studied. First, a comprehensive genome-wide analysis was performed, and 42 GmWRKY genes were identified, which were unevenly distributed in 12 chromosomes. Accordingly, gene structure, collinearity, sequence alignment, phylogenetic, conserved motif and promoter analyses were performed, and the GmWRKY proteins were divided into three subfamilies based on phylogenetic and multiple sequence alignment analyses. Moreover, the enzyme-encoding genes of the secoiridoid biosynthesis pathway and their promoters were then analysed, and the contents of the four secoiridoids were determined in different tissues. Accordingly, correlation analysis was performed using Pearson's correlation coefficient to construct WRKY gene-enzyme-encoding genes and WRKY gene-metabolite networks. Meanwhile, G. macrophylla seedlings were treated with methyl jasmonate (MeJA) to detect the dynamic change trend of GmWRKYs, biosynthetic genes, and medicinal ingredient accumulation. Thus, a total of 12 GmWRKYs were identified to be involved in the biosynthesis of secoiridoids, of which 8 (GmWRKY1, 6, 12, 17, 33, 34, 38 and 39) were found to regulate the synthesis of gentiopicroside, and 4 (GmWRKY7, 14, 26 and 41) were found to regulate the synthesis of loganic acid. Taken together, this study systematically identified WRKY transcription factors related to the biosynthesis of secoiridoids in G. macrophylla, which could be used as a cue for further investigation of WRKY gene functions in secondary metabolite accumulation.