Crucial Chemical Pathway in Plants Traced Back to Ancient Groups of Bacteria

A fundamental chemical pathway that can be found in all plants has now been traced back to two groups of ancient bacteria. The findings reveal a bit more about the evolution of these pathways and could lead to future advances in plant science.

"We have been trying to unravel the source of the phenylalanine amino acid for some time," said Hiroshi Maeda, one of the researchers, in a news release. "Plants use this pathway to make natural products that are vital to plants and also to our food, medicine, fiber and fuel. One of the most important is lignin, found in the plant cell wall, which allows trees to stand tall and transport water."

In order to learn a bit more about plant metabolic pathways, the researchers compared the genetic sequence for the plant phenylalanine pathway enzymes to a genetic database covering numerous organisms. A computer program then narrowed down the choices to similar sequences, which the scientists narrowed down even further with phylogenetic analysis.

In the end, the scientists found that the plant sequence was the most similar to a class of bacteria called Chlorobi and Bacteroidetes.

"This was surprising because when people do a similar analysis for other plant genes, they usually find the closest sequence in fungi, or in cyanobacteria whose ancestor came into plants and now make plants green and photosynthetic," said Maeda. "Our results did not fit what people expected."

The scientists then followed up their findings by arranging the protein sequences from other organisms according to how closely they resembled the plant sequence. In the end, they identified two amino acid sites that are crucial for phenylalanine production.

"The enzyme that plants adopted from the ancient bacteria was helpful to them when they acquired it, and plants ended up maintaining it, rather than other types from fungi or cyanobacteria," said Maeda. "This enzyme and its pathway are now seen across the plant kingdom and allows plants to make such a large variety and quantity of phenolic compounds."

The findings reveal a bit more about plants, which may be crucial for future research. Because the phylalanine pathway is critical to the production of so many valuable plant products, it could potentially be used to help increase the production of nutrients and medicinal compounds.

The findings are published in the journal The Plant Cell.