An ABA-responsive transcription factor SmbZIP38 positively regulates salvianolic acids biosynthesis and stress-associated morphogenesis of Salvia miltiorrhiza

Abstract

Salvia miltiorrhiza Bunge (danshen in Chinese) is a valuable medicinal crop. It is widely used clinically in the treatment of cardiovascular and cerebrovascular diseases. Basic region-leucine zippers (bZIPs) are evolutionarily conserved transcription factors in plants. Here, SmbZIP38, an abscisic acid (ABA)-responsive Group A member of bZIPs, was isolated from S. miltiorrhiza and functionally studied. Overexpression of SmbZIP38 in S. miltiorrhiza hairy roots (SmbZIP38-OE) increased the content of salvianolic acids, while inhibition of its expression in S. miltiorrhiza hairy roots (SmbZIP38-RNAi) decreased the accumulation of salvianolic acids. Meanwhile, SmbZIP38 overexpressing danshen plantlets have well-developed root system, reduced leaf area and size, and increased number of leaves. Transcriptomic analysis revealed differentially expressed genes in SmbZIP38-OE and SmbZIP38-RNAi hairy roots were significantly enriched in both defense and stress response-related pathways as well as phenylpropanoid biosynthesis. Yeast hybridization, electrophoretic mobility shift assay, and dual-luciferase expression assay showed that SmbZIP38 could form homodimers and bind to the ABRE element of the SmTAT promoter region and activate SmTAT transcription. This study demonstrated that SmbZIP38 acts as a positive regulator in salvianolic acids biosynthesis as well as in the morphological construction of S. miltiorrhiza roots and leaves, favoring resistance to abiotic stresses, which indicates that SmbZIP38 is a potential transcription factor to improve the crop quality properties of S. miltiorrhiza.