Researchers Find Important Clue in the Evolution of Plants

Contact: F. Robert Tabita, (614) 292-4297; [email protected] Written by Darrell E. Ward, (614) 292-8456; [email protected]

RESEARCHERS FIND IMPORTANT CLUE IN THE EVOLUTION OF PLANTS

COLUMBUS, Ohio - Scientists have long known that plants and certain microorganisms use an important protein to convert carbon dioxide from the air into useable carbon. What they haven't understood was how plants and bacteria learned to do this.

Now, researchers investigating green sulfur bacteria - microbes capable of breaking down sulfur compounds- have uncovered a new link they believe to be an ancestor of that carbon-fixing protein.

The study was published in the April 10 issue of the Proceedings of the National Academy of Science and funded by grants from the National Institutes of Health and the Department of Energy.

The discovery could lead to a better understanding of how modern plants and microorganisms evolved the ability to use CO2, and it might even suggest ways to improve plants' carbon-absorbing ability -- an important possibility in the present era of greenhouse warming.

In addition, it should give researchers a better understanding of how bacteria break down sulfur compounds and might perhaps lead to faster-growing plants help enhance agricultural productivity.

The link is known as the "RubisCO-like protein." In structure, it strongly resembles the protein known as RubisCO, which modern plants and various bacteria use to convert CO2 to organic carbon.

"We were surprised to find the RubisCO-like protein in green sulfur bacteria," said F. Robert Tabita, professor of microbiology and plant biology at Ohio State University. Thomas E. Hanson, a post-doctoral student, was co-author on the paper.

"This finding gives us an idea as to how the CO2-fixation protein originated, and tells us that it may have had different functions before it evolved into a protein that does what it does today."

Green sulfur bacteria are found in many environments, including stagnant areas of lakes, in rice paddies, in the oceans, and in sand just beneath the surface. They take energy from sunlight and break down, or oxidize, sulfur compounds in the absence of oxygen, converting them into other compounds, said Tabita.

He and Hanson were using a database of bacterial genomes, studying the genome of a species of green sulfur bacteria, when they discovered that a gene sequence in the bacterium resembled the sequence for the RubisCO protein.

The researchers then shut down the gene to learn what the organism would do in the gene's absence.

"That led us to its function in sulfur metabolism," said Tabita, who is also director of Ohio State's Plant-Microbe Genomics Facility and Plant Molecular Biology/Biotechnology Program. The work also suggested that the protein was involved in the bacterium's response to stress.

"Finally, it led us to believe that this protein might be an evolutionary precursor to the RubisCO protein that developed later in plants."

Tabita and Hanson are now trying to identify the specific role the protein plays in sulfur metabolism. They are also studying the molecular control of the stress response.

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