| Abstract Detail
Phytochemical Suttiyut, Thiti [1], Auber, Robert [2], Wisecaver, Jennifer [3], Widhalm, Joshua [4]. Investigating the biochemical evolution and metabolic connections of the shikonin biosynthesis in red gromwell (Lithospermum erythrorhizon). Shikonin is 1,4-naphthoquinones produced exclusively in Boraginaceae species. The compound and its derivatives are predominantly made in roots where they function in mediating plant-plant (allelopathic) and plant-microbe interactions. Moreover, this compound has been a target for drug development due to its strong anti-cancer properties. Our recent assembly and analysis of Lithospermum erythrorhizon genome uncovered metabolic innovation events that contributed to the evolution of the shikonin biosynthesis. This metabolic innovation also reveals the evolutionary link between shikonin biosynthesis and ubiquinone biosynthesis, part of the central metabolisms. In fact, shikonin biosynthesis shares the same precursors and has similar pathway architecture with ubiquinone biosynthesis suggesting that there might be more connections between these two pathways. To gain more insight, we used a transcriptome-based network analysis which uncovered a shikonin gene network model that predicts strong associations between primary metabolic pathway genes and known shikonin biosynthesis genes, as well as links with uncharacterized genes. One of the candidates predicted by the network model was L. erythrorhizon geranyldiphosphate (GPP) synthase (LeGPPS), which encodes a cytoplasmic enzyme shown in vitro to produce GPP. we used RNAi-downregulation to knockdown expression of LeGPPS in L. erythrorhizon hairy roots resulting in reduced shikonin content without affecting expression of the canonical plastid-localized GPPS. This result provides functional evidence that cytoplasmic LeGPPS supplies GPP precursor to the shikonin pathway. Downregulation of LeGPPS also increased ubiquinone content, further supporting our hypothesis on the metabolic and evolutionary connection between shikonin and ubiquinone biosynthesis. RNA-seq analysis of LeGPPS-RNAi lines revealed that downregulating LeGPPS reduces the expression of upstream genes in the mevalonic acid (MVA) pathway and increases expressions of genes involved in isopentenyldiphosphate (IPP) utilization. It also showed that downregulating LeGPPS significantly reduces expression of benzenoid/phenylpropanoid genes, indicating the presence of factors that coordinately regulate the pathways providing the 4-hydroxybenzoic acid and GPP precursors to the shikonin pathway. In addition to LeGPPS, we also found Coenzyme Q4-like gene (LeCOQ4-L) which provided another evolutionary link between shikonin and ubiquinone biosynthesis. The canonical COQ4 is known to provide the structural integrity for ubiquinone biosynthesis. With the existing connections between shikonin and ubiquinone biosynthesis, it is possible that shikonin biosynthesis requires LeCOQ4-L as a structural protein to function efficiently. In addition to investigating the biochemical evolution of the shikonin biosynthesis, our study demonstrates that global coexpression analysis with limited transcriptomic data generated from well-designed experiments is effective for uncovering gene associations within a defined metabolic network.
1 - Purdue University, Department Of Horticulture And Landscape Architecture, 625 Agriculture Mall Dr, West Lafayette, IN, 47907, United States
2 - 125 South University Street, West Lafayette, IN, 47907, United States
3 - 175 South University St, West Lafayette, IN, 47907, United States
4 - Purdue University, Horticulture And Landscape Architecture, 625 Agricultural Mall Drive, West Lafayette, IN, 47907, United States
Keywords:
shikonin
ubiquinone
metabolic origin
metabolic innovation.
Presentation Type: Poster
Number: PPM004
Abstract ID:1175
Candidate for Awards:Phytochemical Best Poster Award |
