Alternative splicing of tanshinone synthesis genes and related splicing factors in Salvia miltiorrhiza in response to hormones

Phytohormones have been shown to stimulate tanshinone synthesis in Salvia miltiorrhiza Bunge. Alternative splicing (AS) and splicing factors (SFs) play crucial roles in the regulation of metabolic processes in response to hormonal signals. However, whether hormones affect tanshinone synthesis through AS remains unclear. In this study, we first screened the existing AS events in tanshinone-associated genes in S. miltiorrhiza, utilizing the transcriptome from hairy roots or roots treated with abscisic acid (ABA), gibberellin (GA), indole-3-acetic acid (IAA), and methyl jasmonate (MeJA). Our analysis identified 12 tanshinone-associated genes harboring alternative spliced isoforms, resulting in a total of 38 AS events. Notably, seven of these events demonstrated dynamic responses to hormones, including SmbHLH3;A3, which was influenced by both MeJA and ABA. Furthermore, the SFs related to those AS events were identified through correlation analysis. A serine/arginine-rich SF stood out with a positive association with many genes involved in tanshinone synthesis, including SmbHLH3. Additionally, we employed weighted gene correlation network analysis (WGCNA) to investigate other AS events potentially involved in tanshinone regulation in response to hormones. The event LOC130987356;A5, which was commonly regulated by ABA, GA, IAA, and MeJA, was an important candidate, with its associated gene module enriched in terpenoid backbone biosynthesis pathway, the critical upstream process in tanshinone production. These findings advance our understanding of the role of AS in the regulation of tanshinone synthesis in response to phytohormones, and facilitate the further exploration aimed at modulating tanshinone production.