Table_4_SmMYC2b Enhances Tanshinone Accumulation in Salvia miltiorrhiza by Activating Pathway Genes and Promoting Lateral Root Development.docx

Salvia miltiorrhiza Bunge (Lamiaceae) is an economically important medicinal plant as well as an emerging model plant. Our previous studies indicate that SmMYC2b is a positive transcription factor that can affect the biosynthesis of phenolic acids and tanshinones in S. miltiorrhiza. Moreover, MYC2s are well known to induce the development of lateral roots. As tanshinones are mainly distributed in the periderm, the promotion of lateral root development probably leads to increased accumulation of tanshinones. In this paper, we firstly discovered that SmMYC2b played a dual regulatory role in effectively enhancing the tanshinone accumulation by activating tanshinone biosynthetic pathway and promoting lateral root development. The expression levels of the previously studied pathway genes SmCPS1, SmKSL1, SmCYP76AH1, SmCYP76AH3, and SmCYP76AK1 dramatically increased. In addition, SmMYC2b was proved to exhibit a similar function as other homologs in promoting lateral root development, which increased the tanshinone produced tissue and further enhanced the biosynthesis of tanshinones. RNA-seq assays revealed that SmMYC2b-regulated genes comprised 30.6% (1,901 of 6,210) of JA-responsive genes, confirming that SmMYC2b played a crucial role in transcriptional regulation of JA-regulated genes. Overall, we concluded that SmMYC2b could enhance tanshinone accumulation by activating the tanshinone biosynthetic pathway and promoting lateral root development. Our study provides an effective approach to enhance the production of desired tanshinones and enriches our knowledge of the related regulatory network.

丹参（Salvia miltiorrhiza Bunge）隶属于唇形科（Lamiaceae），是兼具重要经济价值的药用植物与新兴模式植物。本团队既往研究表明，SmMYC2b是一类正向转录因子，可调控丹参中酚酸类物质与丹参酮的生物合成过程。此外，MYC2家族成员诱导侧根发育的功能已被广泛证实。由于丹参酮主要分布于周皮组织中，促进侧根发育或可提升丹参酮的积累量。本研究首次发现，SmMYC2b可通过双重调控机制有效提升丹参酮积累：一方面激活丹参酮生物合成通路，另一方面促进侧根发育。经检测，已报道的通路关键基因SmCPS1、SmKSL1、SmCYP76AH1、SmCYP76AH3及SmCYP76AK1的转录水平均显著上调。此外，研究证实SmMYC2b与其他同源蛋白功能类似，可通过促进侧根发育扩大丹参酮的合成组织范围，进一步提升丹参酮的生物合成效率。RNA测序（RNA-seq）分析显示，受SmMYC2b调控的基因中，有30.6%（6210个基因中的1901个）为JA响应基因，这证实SmMYC2b在JA介导的基因转录调控中发挥关键作用。综上，本研究明确SmMYC2b可通过激活丹参酮生物合成通路并促进侧根发育，进而提升丹参酮的积累量。本研究为定向提升目标丹参酮的产量提供了有效策略，同时丰富了相关调控网络的认知。