Recreate metabolic evolution in plants

Plants have evolved to produce a variety of compounds that vary from one species to another. These compounds play a key role in plant survival strategies. Compounds that are bitter and toxic prevent plants from being eaten by insects and animals. Meanwhile, odorous compounds or colored pigments attract insects carrying pollen.

Of the compounds produced by plants, some have medicinal uses because of their physiological effects on the human body. Researchers have reported that the matrine could be used as a depressant of the central nervous system, like morphine, and that hperizin A could also be used as an adjunct in the treatment of Alzheimer 's disease. ; Alzheimer's. These compounds are called alkaloids, which are also metabolites produced from the amino acid lysine in some plant species.

Now, how has the alkaloid system derived from lysine evolved in plants? In 2016, the research team of Chiba University discovered that lysine-derived alkaloid-producing plants possess particular enzymes that possess bifunctional decarboxylating activity towards ornithine. and lysine (lysine / ornithine decarboxylase). These enzymes were developed by a micro-mutation of the ancient enzyme (ornithine decarboxylase), essential for the production of polyamine used in fundamental and biological activities, such as cell division, in various organisms. These enzymes can decarboxylate and activate lysine, an amino acid, and then send it to the production of alkaloids in plant cells. Micro-mutation is crucial for metabolism producing alkaloids and is common for plants using lysine as a material for the production of alkaloids.

Since this discovery in 2016, the research team expects the micromated enzyme to be a key factor in the evolution of plants for the production of some type of disease. Alkaloid, this mutation being visible only in plant species producing alkaloids derived from lysine. .

Finally, research teams from the University of Chiba, RIKEN and the Kazusa DNA Research Institute confirmed in an article published in the Plant Journal of July 31, 2019 that alkaloids had been generated by inserting the gene of the Lysine / ornithine decarboxylating enzyme of Lupinus angustifolius producing lysine. alkaloid derived in Arabidopsis thaliana (A. thaliana). The team also identified the type of metabolites newly generated in A. thaliana, a model plant initially devoid of the function to produce an alkaloid.

It is worth noting that the research team recreated the metabolic evolution of the alkaloid-producing plant in a model plant. A. thaliana has been transformed to produce alkaloids by inserting the gene of the enzyme to modify the metabolic flux. The expression of the introduced gene in A. thaliana resulted in the production of cadaverine (1,5-diaminopentane) from lysine, which is then metabolized by endogenous enzymes. These processes led to the generation of new alkaloid-related metabolites; 5-aminopentbad, 5-aminopentanoic acid and δ-valerolactam of A. thaliana.

It is interesting to note that the research team identified the newly generated substances by detecting metabolite changes before and after the introduction of the gene, which is a daunting task since plants typically contain several thousand metabolites.

"We have been able to modify the metabolic flow by manipulating one of the genes in the plant and by identifying the types of alkaloids generated in the cells, which is a big step forward for the next discovery," he said. said Mami Yamazaki, an badociate professor at Chiba. University, who led the experiment. "Our research has opened the door to the possibility of producing new compounds, which do not yet exist in nature, by carrying out a similar genetic engineering on plants with different metabolic capacity potentials." This expansion of diversity chemical is an important theme for the development of seeds in the pharmaceutical industry ".

The research team hopes that the elucidation of the metabolic mechanism in plants with the recently developed method will result in a stable intake of medical ingredients over the next few years.

Reference: Shimizu et al. 2019. Metabolic diversification of nitrogen-containing metabolites by the expression of a heterologous lysine decarboxylase gene in Arabidopsis. The journal of plants. https://doi.org/10.1111/tpj.14454.

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