Fundamental Plant Chemicals Rooted in Bacteria

A fundamental chemical pathway that all plants use to create the essential amino acid phenylalanine has now been traced to two groups of ancient bacteria, a new study reports.

"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," Hiroshi Maeda, an assistant professor of botany at the University of Wisconsin-Madison, explained in a university news release.

Scientists were surprised to find that this particular metabolic pathway was tied to bacteria, given that so many others are linked with fungi or cyanobacteria, "which are pretty close to plants in terms of evolution," Maeda said.

In the journal The Plant Cell, Maeda and his colleagues described how they traced the phenylalanine pathway to two groups of bacteria. They compared the genetic sequence for the plant phenylalanine pathway enzymes to a genetic database covering numerous organisms.

"We asked the computer to fish out similar sequences, and we got thousands of sequences," Maeda said. "We took the closer sequences and did phylogenetic analysis. Essentially we were asking, 'Who is your closest sibling?'"

They found that the plant sequence was most similar to a class of bacteria called Chlorobi and Bacteroidetes.

"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," Maeda noted.

The researchers followed up this result by arranging the protein sequences from other organisms according to how closely they resembled the plant sequence, and identified two amino acid sites that are crucial for phenylalanine production.

Since the phenylalanine pathway is crucial to the production of so many valuable plant products, Maeda believes these findings can eventually lead to practical applications.

"We hope this might help increase production of nutrients and medicinal compounds," he added.