SmTIR1 positively regulates the growth and root development of Salvia miltiorrhiza

Abstract The roots of Salvia miltiorrhiza are widely used as medicinal materials in China and other East Asian countries. Root morphology and development are important factors that affect the quality and yield of this herb, but the molecular mechanism underlying root morphogenesis in S. miltiorrhiza remains elusive. Auxin is one of the main phytohormones that regulate root development in plants, and auxin receptor transport inhibitor response 1 (TIR1) plays pivotal roles in this biological process. In this study, SmTIR1 gene was cloned and transgenic S. miltiorrhiza plantlets were obtained to investigate the function of SmTIR1 in root development of S. miltiorrhiza. As the results shown, SmTIR1 positively regulated the growth and root development in S. miltiorrhiza. The SmTIR1 overexpression lines showed increased leaf number, root biomass, lateral root number, and lateral root diameter. The SmTIR1 RNAi lines showed the opposite morphological indices compared with the SmTIR1 overexpression lines. Besides, the contents of phenolic acids in leaves of SmTIR1 overexpression lines were remarkedly increased, but accumulation of bioactive compounds in roots of SmTIR1 transgenic S. miltiorrhiza was did not altered compared with the control. The RNA-seq analysis was performed and a total of 26 differential expressed genes in the auxin signaling pathway were identified in SmTIR1 RNAi lines, these genes may be relevant to the SmTIR1 regulated growth and root development in this species. Our results shed new light on the molecular mechanism of root morphogenesis of S. miltiorrhiza and is helpful to improve the quality of this herb with biological method in the production practice.