Downregulation of Cinnamoyl CoA Reductase Affects Lignin and Phenolic Acids Biosynthesis in Salvia miltiorrhiza Bunge

Abstract

The biosynthesis of salvianolic acid B shares the phenylpropanoid pathway with lignin, and cinnamoyl CoA reductase (CCR; EC 1.2.1.44) is a specific enzyme in the lignin pathway. In this study, a CCR gene (SmCCR1) from Salvia miltiorrhiza Bunge was cloned using DNA walking technology (GenBank ID: JF798634). The full-length SmCCR1 is 2,489 bp long and consists of four introns and five exons encoding a polypeptide of 324 amino acid residues. Sequence alignment revealed that SmCCR1 shares 83 % identity with CCR sequences reported in Camellia oleifera and other plant species. Expression pattern analysis indicated that expression of SmCCR1 can be induced by exposure to Xanthomonas campestris pv. Campestris or methyl jasmonate. To demonstrate its functioning, we selected a 296-bp fragment and established an RNA interference construct that was introduced into S. miltiorrhiza by Agrobacterium tumefaciens-mediated gene transfer. Transgenic plants exhibited dwarfing phenotypes, and both syringyl and guaiacyl lignin monomers were decreased more than 60 %. In contrast, biosynthesis of phenolic acids—danshensu, rosmarinic acid, and salvianolic acid B—was strongly induced by 2.03-, 1.41-, and 1.45-fold, respectively, in the roots of transgenic plants from line CCR-10. Consistent with these phytochemical changes, downregulation of SmCCR1 also affected the expression of related genes in the phenolics and lignin biosynthetic pathways. Our results also provide potential opportunities for engineering danshensu and salvianolic acid B production in S. miltiorrhiza.