Methyl 3-(4-hydroxyphenyl) propionate modulates plant growth and secondary metabolite accumulation by inducing metabolic changes in Perilla frutescens

As one of the components of root exudates, methyl 3-(4-hydroxyphenyl) propionate (MHPP) not only functions as a nitrification inhibitor in soil but also modulates plant growth and root system architecture (RSA); however, the physiological and molecular mechanisms underlying MHPP-mediated plant growth remain largely unclear. Here, we investigated the effects of MHPP treatment on growth and secondary metabolite accumulation by integrating physiology, transcriptome and metabolome analyses using perilla (Perilla frutescens), a type of medicinal and edible plant. MHPP reduces primary root growth but markedly induces lateral root formation in perilla seedlings. The full-length transcript sequencing combined with the comparative transcriptomic analysis revealed that the differential expression of genes involved in carbon/nitrogen metabolism and secondary metabolism contributed to the MHPP-mediated plant growth. An investigation of the differentially expressed genes showed that MHPP modulates the growth and metabolism of leaves and roots in distinct pathways. The genes involved in the phenylpropanoid metabolism pathway showed opposite expression patterns between the roots and leaves, thereby resulting in the differential accumulation of secondary metabolites in the roots and leaves. Furthermore, the differential expression of PER genes and elevated peroxidase activity in the MHPP-treated roots were responsible for modulating the equilibrium of ROS and the components of lignin and phenolic compounds, thereby affecting plant growth and secondary metabolite accumulation. MHPP modulates RSA and metabolite profiles and improves the contents of medicinal ingredients in perilla plants. These results suggested that the application of MHPP may represent a useful strategy for the medicinal plant cultivation.