Profiling of the Major Phenolic Compounds and Their Biosynthesis Genes in Sophora flavescens Aiton

Abstract

Sophorae Radix (Sophora flavescens Aiton) has long been used in traditional medicine in East Asia due to the various biological activities of its secondary metabolites. Endogenous contents of phenolic compounds (phenolic acid, flavonol, and isoflavone) and the main bioactive compounds of Sophorae Radix were analyzed based on the qualitative HPLC analysis and evaluated in different organs and at different developmental stages. In total, 11 compounds were detected, and the composition of the roots and aerial parts (leaves, stems, and flowers) was significantly different. trans-Cinnamic acid and p-coumaric acid were observed only in the aerial parts. Large amounts of rutin and maackiain were detected in the roots. Four phenolic acid compounds (benzoic acid, caffeic acid, ferulic acid, and chlorogenic acid) and four flavonol compounds (kaempferol, catechin hydrate, epicatechin, and rutin) were higher in aerial parts than in roots. To identify putative genes involved in phenolic compounds biosynthesis, a total of 41 transcripts were investigated. Expression patterns of these selected genes, as well as the multiple isoforms for the genes, varied by organ and developmental stage, implying that they are involved in the biosynthesis of various phenolic compounds both spatially and temporally.

Figure 1

(a) A schematic presentation of general flavonoid biosynthetic pathway. Multiple arrows indicate two or more steps in the pathway, and flavonoids that analyzed in this study are highlighted in red. PAL, phenylalanine ammonia lyase; CNL, cinnamoyl-CoA ligase; C4H, cinnamic acid 4-hydroxylase; C3H, p-coumaroyl ester 3-hydroxylase; COMT, caffeic acid 3-O-methyltransferase; 4CL, 4-coumaroyl:CoA-ligase; CHS, chalcone synthase; CHR, chalcone reductase; CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase; F3′H, flavanone 3′-hydroxylase; FLS, flavonol synthase; UFGT, UDP glucose: flavonoid-3-O-glucosyltransferase; FLS, flavonol synthase; DFR, dihydroflavonol 4-reductase; LAR, leucoanthocyanidin reductase; ANS, anthocyanidin synthase; ANR, anthocyanidin reductase; IFS, isoflavone synthase; IOMT, isoflavone O-methyltransferase; I3′H, isoflavone 3′-hydroxylase; I2′H, isoflavone 2′-hydroxylase. (b) Contents of flavonoid compound in roots, leaves, stems, and flowers of Sophorae Radix (ug/g dry weight). R, roots; SL, small leaves; ML, medium leaves; LL, large leaves; SS, small stems; MS, medium stems; LS, large stems; F, flowers.

Figure 2

Semiquantitative RT-PCR transcript analysis of the flavonoid biosynthesis genes in root, leaves, stems, and flower of Sophorae Radix. (a) Phenylpropanoid biosynthetic genes. (b) Phenolic acid biosynthetic genes. (c) Flavonoid biosynthetic genes. (d) Isoflavonoid biosynthetic genes. Transcript levels were determined after normalization with Actin11 as the reference gene. R, root; SL, small leaf; ML, medium leaf; LL, large leaf; SS, small stem; MS, medium stem; LS, large stem; F, flower.