Comparative transcriptome analysis and identification of candidate bZIP transcription factors involved in anthraquinone biosynthesis in Rheum officinale Baill.

Rhubarb is a traditional medicinal plant in China, whose pharmacological effects derive mainly from its anthraquinones. However, the regulatory mechanism affecting anthraquinone biosynthesis in R. officinale remains poorly understood. We assembled a high-quality, full-length transcriptome using single-molecule real-time (SMRT) sequencing. 274 unigenes potentially involved in the biosynthesis of anthraquinones, including those in the shikimate, polyketide, MVA and MEP pathways, were identified based on full-length transcriptome. Differentially expressed genes (DEGs) induced by MeJA treatment and DEGs between different tissues were identified through next-generation sequencing (NGS), revealing the genes that may be involved in the biosynthesis of anthraquinones. The basic leucine zipper (bZIP) transcription factors of R. officinale were systematically identified. Key genes such as RobZIP50 and RobZIP53 were systematically identified and found to be associated with anthraquinone biosynthesis in R. officinale through differential expression, co-expression and protein interaction analyses. RobZIP50 and RobZIP53 were highly expressed in roots and rhizomes, and significantly increased after 12 h of MeJA treatment. Additionally, both RobZIP50 and RobZIP53 were localized exclusively in the nucleus, with RobZIP53 showing significant transcriptional activity. Taken together, our results suggest that RobZIP53 may play a role in regulating anthraquinone biosynthesis in R. officinale.