An international team of researchers from the University of Georgia and the Max Planck Institute (MPI) for chemical ecology in Germany has uncovered a promising strategy for decoding metabolic pathways for plant compounds important in medical treatments, according to a new study published in Nature Chemical Biology.
Led by Chenxin Li of the Center for Applied Genetic Technologies at UGA’s College of Agricultural and Environmental Sciences, the research team studied the biosynthesis of two alkaloids from the Madagascar periwinkle (Catharanthus roseus) that are used as anticancer agents in human medicine. . The genes for the formation of these active substances are expressed in different cell types. Using single-cell analyses, the scientists were able to discover new genes important for biosynthesis and show that metabolic pathway intermediates accumulate in specific cell types. Intermediates are molecules that are the precursors or metabolites of biologically significant molecules.
The researchers expect that this methodological approach will provide important new insights into the biosynthesis of many other natural products of the plant kingdom.
Plants are impressive in their diversity, especially in the variety of metabolites they produce. Many natural plant products are composed of highly complex molecules, such as the alkaloids vincristine and vinblastine, produced by the Madagascar periwinkle. These two substances are already indispensable in cancer therapy and researchers are interested in finding out which individual biosynthetic steps are required to form the complex molecules.
“Currently, these compounds are still obtained in very small quantities from the plant’s leaf extract. We can learn from the plant how this compound is produced and use this knowledge to develop more cost-effective, scalable and sustainable production systems.” said Li, first author of the study, describing the goal of the research.
Investigate specialized cell types
Scientists know that gene activity differs between plant cells and that chemistry can differ dramatically from cell to cell. The goal of the recent study was to use a new set of methods collectively called single-cell omics to study specialized and rare cell types that play a central role in the biosynthesis of natural plant products and whose signals are often obscured by more abundant cell types. in plant organs.
“With single-cell omics, we have a method that allows researchers to assign genetic and metabolic information to individual cells. The term ‘omics’ refers to the fact that an entire collection of genes or metabolites is quantified and analyzed,” explained Lorenzo Caputi. , head of the Alkaloid Biosynthesis Project Group in the Natural Products Biosynthesis Department at MPI and one of the lead authors.
Understanding of biosynthetic pathways
As the analyzes showed, the entire biosynthetic pathway of the vinblastine alkaloid is organized into three stages and three distinct cell types.
“The first stage is expressed exclusively in specialized cells associated with vascular bundles in the leaf, called IPAP. The second stage of the biosynthetic pathway is expressed only in cells of the epidermis, the layer of cells that cover the leaves, and the last known stages of the biosynthetic pathway are exclusively expressed in idioblasts, a rare cell type in the leaf,” Li summarized.
The researchers measured the concentrations of several intermediates in the vinblastine metabolic pathway in single cells and were surprised by the results.
“Two important precursors of vinblastine catharanthine and vindolin are found in idioblastic cells at millimolar concentrations, about three orders of magnitude higher than vinblastine itself. The concentration of the two precursors in these cells was much higher than we expected and even exceeded the their concentrations in all organ extracts. However, this observation makes sense as catharanthine and vindoline were found only in the rare idioblastic cells. The abundant other cells in the leaf dilute the high concentration when whole leaves are crushed,” said Sarah O’Connor, head of the MPI’s Department of Natural Products Biosynthesis.
New techniques for studying natural products
The research team is confident that the organization of biosynthetic pathways for medically relevant alkaloids in Catharanthus roseus is not an isolated phenomenon. “We are just beginning to understand how and why such cell-type-specific organization exists. Furthermore, analyzing simultaneously expressed genes in a particular cell type has helped us identify new players in this metabolic pathway,” said Robin Buell, of the Georgia Research Alliance (GRA) Eminent Scholar Chair in Crop Genomics at UGA. “The same technique can be used to study the biosynthesis of many other natural products. Finally, the exact sites of accumulation of plant compounds, such as the epidermis, vascular system or latex duct, can help us hypothesize the ecological roles of natural products. For example, depending on the pattern of accumulation, the compounds may be more effective against biting insects than against sap-sucking insects.”
A better understanding of the biosynthetic pathways of the anticancer drugs vincristine and vinblastine may also help produce or harvest these compounds more effectively in the long term. The use of the methods described is also promising for the study of many other interesting and medically important natural products of the plant kingdom.
The approach described in the study will help narrow down these rare and specialized cells and uncover the gene activities and chemistry that are unique to them.
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