Distribution of flavonoids in Paeonia suffruticosa and analyses of the genes involved in flavonoid biosynthesis in plants

Paeonia suffriticosa is a woody peony that is an important medicinal plant in Korea, China, and Japan. Flavonoids are a class of polyphenolic secondary metabolites. We analyzed seven flavonoid compounds in various tissues of Korean landrace P. suffriticosa. Of these, flavonols were more abundant compared with other flavonoids in the roots, leaves, and petals, whereas flavones (apigenin and luteolin) were present in low abundance in all tissues. The root tissues generally contained higher flavonoid content compared with the other tissues. Because molecular analyses of the genes involved in flavonoid biosynthesis genes have not been systematically conducted in P. suffriticosa, we performed a transcriptome analysis, which identified 34,629 unigenes in the transcriptome. Our functional matching results using the NCBI Nr and in EMBL-EBI EMBL Interpro databases were similar to those of previous reports in P. suffriticosa. The highest matching species for the annotated genes was V. vinifera, which was corroborated in reports from other Paeonia species. The genes encoding enzymes in the shikimate pathway and aromatic amino acids biosynthesis genes were identified from the transcriptome data. We also identified homologous genes in other Paeonia species as well as Arabidopsis and rice. The number of gene copies varied from one in DHQS and CS to seven to ten in 4CL. Sequence and phylogenetic analyses revealed that several conserved blocks were observed in 4CLs from nonvascular to vascular plants. A CHS analysis revealed that there were at least three homologs of CHSs in the genus Paeonia. The sequences of the catalytic residues, CoA binding sites, and structural activity of the CHSs were conserved from the basal plant of liverwort to vascular flowering plants. In a phylogenetic analysis of CHS and CHI, the CHSs from the major plant lineages formed their own cluster, whereas CHIs from diverse plant lineages were clustered together. Protein sequences were highly conserved among the CHIs within clades, but diverged between clades. Thus, CHSs of each major plant lineage may have evolved independently following divergence, whereas CHIs in each clade in the phylogenetic analysis may have evolved separately from basal plants to angiosperms.