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San Marcos duo digs into roots


San Antonio Express-News (05/12/2006)
by Cindy Tumiel

Growing a plant appears to be a simple matter — poke a seed into dirt, add sunlight, water and maybe some fertilizer, and green shoots will appear within a matter of days.

But plant geneticists have spent decades trying to understand precisely how this happens. What makes roots grow downward and green shoots aim for the sun? What causes branches to grow and flowers and fruits to form?

San Marcos scientists now have illuminated that picture a bit more, as part of an international team that has described how root cells use auxin, an important hormone that regulates a plant's growth.

Sunethra Dharmasiri and her husband, Nihal Dharmasiri, both of Texas State University, say a protein called AXR4 allows root cells to properly use the growth hormone auxin.

"It regulates how much auxin is going into the cell," said Sunethra Dharmasiri."This protein gets auxin in the right concentrations into the right places in the cell."

The paper, which involved scientists from Indiana University, Sweden and the United Kingdom, was published Thursday by the online journal Science Express.

Scientists have spent decades trying to understand plant genetics, knowledge they say will help botanists develop hardier plants that could be more drought or pest tolerant or able to produce bigger crop yields.

Auxin and its role in proper plant growth was discovered 70 years ago, but only recently have scientists been able to understand exactly how it is transported through a plant.

The Dharmasiris were part of a team at Indiana University that last year identified a key receptor that is the hormone's doorway into the cell. That discovery was considered a breakthrough; Science magazine later included it in its year-end report on the most significant scientific findings of 2005.

Since then, the Dharmasiris were recruited to Texas State, where they have their own laboratory and continue to work on the underlying mechanisms that make plants grow.

Athanasios Theologis, senior scientist at the Plant Gene Expression Center at University of California, Berkeley, said the latest study fills in a little more of the story about how auxin does its job. AXR4 is one of several transporter molecules and understanding of how it works is a significant step, he said.

"This is one more part of the big puzzle," Theologis said.

Knowledge about how these molecules work in plants could potentially offer insights into human medicine as well, he added. It also could help plant biologists learn how to control root growth, Sunethra Dharmasiri said.

"If we know how to regulate auxin, we can manipulate how much of the root system can develop," she said. "If you want to maximize how much the roots can grow, the understanding of this protein certainly can help."