SmKFB5 Protein Regulate Phenolic Acids Biosynthesis via Controlling the Degradation of Phenylalanine Ammonia-Lyase in Salvia miltiorrhiza.

Phenolic acids are the major secondary metabolites and significant bioactive constituents of medicinal plant Salvia miltiorrhiza. Many enzyme-encoding genes and transcription factors involved in phenolic acids biosynthesis have been identified, but the underlying posttranslational regulatory mechanisms are poorly understood. Here, we demonstrated that the S. miltiorrhiza Kelch repeat F-box (KFB) protein SmKFB5 physically interacted with three Phenylalanine Ammonia-Lyase (PAL) isozymes and mediated their proteolytic turnover via the ubiquitination-26S proteasome pathway. Disturbing the expression of SmKFB5 reciprocally affected the abundance of SmPAL protein level and accumulation of phenolic acids, suggesting that SmKFB5 is a posttranslational regulator responsible for the turnover of PAL and negatively controlling phenolic acids. Furthermore, we discovered that treatment of hairy root of S. miltiorrhiza to Methyl jasmonate (MeJA) suppressed the gene expression of SmKFB5 while inducing the transcription of SmPAL1 and SmPAL3. These data suggested that MeJA consolidated both transcriptional and posttranslational regulation mechanisms to enhance phenolic acids biosynthesis. Taken together, our results shed insights into the molecular mechanisms on SmKFB5 mediating Jasmonic acid (JA) regulating phenolic acid biosynthesis and provide valuable targets for plant breeders in tailoring new cultivars.