Rhizobial inoculation promotes glycyrrhizic acid production through jasmonic acid signaling in Glycyrrhiza uralensis.

We previously found that inoculation with rhizobia tends to increase both biomass production and glycyrrhizic acid (GL) production in the medicinal plants Glycyrrhiza uralensis and G. glabra. In this study, we investigated the mechanism by which rhizobial inoculation promotes GL production. Transcriptome analysis of plants grown for 3, 6, 9, and 13 weeks after rhizobial inoculation revealed significant enrichment of GO terms related to root tissue differentiation and reorganization in inoculated plants. In addition, jasmonic acid (JA)-mediated signaling pathway, fatty acid biosynthetic process, and isoprenoid biosynthetic process were specifically enriched in inoculated plants, and these terms included Jasmonate ZIM-domain protein (JAZ)-like, MYC-related transcription factor 2 (MYC2)-like, Allene oxide cyclase (AOC)-like, Allene oxide synthase (AOS)-like, and Squalene synthase 2 (SQS2)-like genes. Time-course analysis of the expression patterns of these genes showed that JAZ-like genes were upregulated at the early growth stages in inoculated plants, whereas at 13 weeks after inoculation, expression of JAZ-like genes decreased while MYC2b and CYP88D6 expression increased. These results suggest that CYP88D6 expression may be regulated by MYC2. These results suggest that activation of JA biosynthesis and JA signaling is involved in the promotion of GL production by rhizobial inoculation, thereby supporting our previously proposed hypothesis at the transcriptome level. Further studies, including JA quantification, elucidation of transcriptional regulatory mechanisms, and functional analyses, will be necessary.