Bupleurum falcatum L. is frequently used in traditional herbal medicine in Asia. Saikosaponins (SSs) are the main bioactive ingredients of B. falcatum, but the biosynthetic pathway of SSs is unclear, and the biosynthesis of species-specific phytometabolites is little known. Here we resolved the transcriptome profiles of B. falcatum to identify candidate genes that might be involved in the biosynthesis of SSs. By isoform sequencing (Iso-Seq) analyses of the whole plant, a total of 26.98 Gb of nucleotides were obtained and 124,188 unigenes were identified, and 81,594 unigenes were successfully annotated. A total of 1033 unigenes of 20 families related to the mevalonate (MVA) pathway and methylerythritol phosphate (MEP) pathway of the SS biosynthetic pathway were identified. The WGCNA (weighted gene co-expression network analysis) of these unigenes revealed that only the co-expression module of MEmagenta, which contained 343 unigenes, was highly correlated with the biosynthesis of SSs. Comparing differentially expressed gene analysis and the WGCNA indicated that 130 out of 343 genes of the MEmagenta module exhibited differential expression levels, and genes with the most “hubness” within this module were predicted. Manipulation of these genes might improve the biosynthesis of SSs.

Bupleurum chinense DC. is a well-known traditional Chinese medicinal plant that produces saikosaponins (SSs), which possess hepatoprotective, antipyretic, and anti-inflammatory activities. Methyl jasmonate (MeJA) is a signalling phytohormone that can increase the accumulation of SSs in the root of Bupleurum plants. However, the molecular understanding of MeJA-mediated SS biosynthesis is not clear. Therefore, it is necessary to explore the molecular mechanism underlying the response of B. chinense DC. to MeJA in roots. In this study, we performed comparative transcriptome analysis of B. chinense DC. roots with different MeJA treatment times. In total, 104,057 unigenes were identified, of which 4053 were differentially expressed genes (DEGs). Most of the DEGs were downregulated after MeJA treatment, and GO enrichment analysis showed that they were mainly related to biological processes involved in stress responses and development. A total of 88 DEGs encoding enzymes known to be involved in the SS synthesis pathway were found, and most were significantly downregulated within 24 h. Based on the DEGs, 99 transcription factors (TFs) belonging to the AP2/ERF, WRKY, bZIP, ZFP, and bHLH families with different expression patterns were also identified. Further integrated analysis indicated that 20 DEGs involved in the SS synthesis pathway and 12 DEGs encoding TFs presented strong correlations with the SS contents, and these DEGs may be critical for the biosynthesis and regulation of SSs. These findings will be critical for further study of the response of B. chinense DC. to MeJA for SS biosynthesis.

Although DNA elimination, gene silencing and duplication and pseudogenization are associated with allopolyploidization in wheat, the effect of allopolyploidy on the ecogeographical expansion and domestication of this species remains unknown. In the present study, we used 1862 mapped loci to investigate genetic changes associated with allopolyploidization by comparing bands between synthetic wheat SHW-L1 and its parental lines Aegilops tauschii ssp. tauschii AS60 (DD) and Triticum turgidum ssp. turgidum AS2255 (AABB). A total of 338 (18.15%) loci from AS60 or AS2255 were found to have been eliminated from SHW-L1. Of these loci, 56 were present only in AS2255; 212 ones were found only in AS60 and 70 ones were detected in both AS2255 and AS60. The different numbers of eliminated loci originating from AS2255 and AS60 suggest that the D genome of SHW-L1 suffered more disruption during the allopolyploidization process than the A and B genomes. In addition, 82 eliminated loci were tightly linked to express quantitative trait loci, with 53 of these loci containing open reading frame sequences predicted to encode proteins related to disease resistance, environmental adaption, nitrogen fixation, nitrogenase reductase and other processes. Further investigation of changes in these gene sequences should help elucidate the genetic mechanisms underlying the increased fitness, adaptability and competitiveness that have accompanied wheat during domestication.