A recent study has unveiled the independent evolution of pathways in plants to produce the same substance for defense.
“Enzymes that catalyze the same chemical reaction can evolve independently many times,” wrote the study authors.
“However, examples of independent evolution of an entire pathway that consists of many enzymatic steps are rare. In this manuscript, we report the discovery of two biosynthetic pathways that both synthesize a class of plant defensive molecule called benzoxazinoid.”
Benzoxazinoids are crucial for maize plants. Serving as a defense against herbivores, they suppress their appetite while also possessing antimicrobial properties.
Furthermore, these compounds play a role in facilitating interactions between plants. Their production process in maize has been familiar to researchers since the 1990s.
However, what’s remarkable is that even though specialized metabolites often are seen in related plant species, benzoxazinoids deviate from this trend. They appear sporadically across numerous unrelated plant families.
A team of researchers led by Tobias Köllner at the Max Planck Institute for Chemical Ecology set out to investigate this peculiar behavior. The goal was to determine whether different species developed the ability to form benzoxazinoids independently of each other.
The researchers explored two unrelated eudicot plant species known for producing benzoxazinoids: the golden dead-nettle Lamium galebodolon and the zebra plant Aphelandra squarrosa.
The team developed comprehensive datasets of the compounds and genes expressed in different tissues of these plants.
By contrasting them with related species that don’t produce benzoxazinoids, they were able to pinpoint potential genes that might be implicated in the formation of these compounds.
“This approach allowed us to identify candidate genes that may be involved in the formation of these compounds,” explained study first author Matilde Florean.
“We further characterized the candidate genes by expressing them in tobacco to find out if they are really involved in the production of benzoxazinoids.”
The results were surprising. The study revealed that the metabolic pathway of benzoxazinoids evolved independently in maize, the golden dead-nettle, and the zebra plant.
Unlike in maize, where a set of closely related cytochrome P450 enzymes handle specific steps, the golden dead-nettle and the zebra plant employ entirely different enzyme classes.
Remarkably, these two plants utilize a dual-function flavin-containing monooxygenase for this process, instead of the two separate cytochrome P450 enzymes observed in grasses.
“With this work, we have shown how flexible plant metabolism can be. We have shown that plants can independently invent very different strategies to make the same chemical compounds, and this has happened at least three times in the evolutionary history of benzoxazinoids,” said Sarah O’Connor, the director of the Department of Natural Product Biosynthesis.
The research team’s next goal is to explore the biosynthesis of benzoxazinoids in a broader range of plant families.
The research is published in the journal Proceedings of the National Academy of Sciences.
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