Table_3_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，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。我们前期研究证实，SmMYC2b为正向转录因子，可调控丹参中酚酸与丹参酮的生物合成。此外，MYC2家族基因已被广泛报道可诱导侧根发育。由于丹参酮主要分布于周皮组织，促进侧根发育或可提升丹参酮的积累水平。本研究首次发现，SmMYC2b可通过激活丹参酮生物合成通路并促进侧根发育，对丹参酮积累发挥双重调控作用。此前已研究的通路基因SmCPS1、SmKSL1、SmCYP76AH1、SmCYP76AH3及SmCYP76AK1的表达量均显著上调。此外，实验证明SmMYC2b与其他同源基因功能相似，可通过促进侧根发育扩增丹参酮的合成组织，进一步增强丹参酮的生物合成。RNA测序（RNA-seq）分析显示，受SmMYC2b调控的基因占茉莉酸（JA）响应基因总数的30.6%（6210个基因中含1901个），证实SmMYC2b在茉莉酸介导的基因转录调控中发挥关键作用。综上，本研究认定SmMYC2b可通过激活丹参酮生物合成通路并促进侧根发育，提升丹参酮的积累量。该研究为定向提高目标丹参酮产量提供了有效策略，同时丰富了相关调控网络的认知。