Professor finds key to plant growth

We all know how plants grow. You put a seed in the dirt, you water the dirt for a while, and with a little bit of sunshine and patience you get a plant. \nOf course, it's a little more complicated than that. \nBut for a process that seems so simple, a great deal of mystery surrounds the biological process of plant growth.\nIU researchers Mark Estelle, Nihal Dharmasiri and Sunethra Dharmasiri have solved a large part of the puzzle by unlocking some of the mystery surrounding the hormone auxin, which has been known to play an important role in the growth of plants for many years. \nCharles Darwin began research on plant growth in 1880 by writing a book entitled "The Power of Movement in Plants," according to www.plant-hormones.info. Darwin began his research after observing that grass seemed to grow toward its source of sunlight. Since then, auxin, which takes its name from the Greek word for "to grow," has been identified as an important component of plant growth and is known to be responsible for several plant functions, including the upward growth of stems and the downward growth of roots. But little was known about how the substance worked to create these results. \nEstelle, who teaches a course in genetics at IU, set out to understand the nature of auxin nearly 20 years ago. \n"We've known that auxin exists since the 1930s, so this is a very old problem in plant biology," he said. "People have been trying to understand this for decades."\nEstelle said the key to understanding how auxin works was identifying auxin's receptor. \n"What we've learned recently is that auxin works through a protein which is called TIR1," he said. "TIR1 functions as the receptor for auxin, so plant hormones work in a way that at least, generally, is similar to animal hormones: they interact with a receptor. And so the recent discovery is what that receptor is."\nEstelle said he and his colleagues performed experiments on Arabidopsis thaliana, a plant more commonly known as thale cress. They identified the receptor by showing that radioactively-labeled auxin binds to TIR1; in simpler terms, the researchers highlighted auxin in order to trace it and discover where it binds. \nAlthough the results are only now being published, Estelle said the culmination of their research began last spring. \n"We were really, really excited," he said. "These kind of discoveries often occur over a period of months, but I guess it was about a year ago when Nihal (Dharmasiri) obtained the results which suggested that TIR1 really was the receptor. It takes some months for all these things to happen." \nDharmasiri is a post-doctoral research associate who has worked with Estelle for nearly six years, along with his wife, Sunethra. He said the TIR1 receptor is part of a protein complex, known as an SCF complex, that exists in many other organisms. Because the findings show that an SCF complex can be controlled by a regulatory molecule, Dharamasiri said he expects the influence of the results to be considerable. \n"This will have a tremendous impact not only on plant research, but on other areas such as health research," he said. "There will be many practical applications down the road ... knowing how plants recognize auxin could be useful in controlling the plant growth we desire. This finding will have an impact on the herbicide industry too." \nThe discovery of auxin's receptor is an important turning point in the science of plants, but Dharmasiri said his interest in the research was motivated by scientific curiosity rather than personal or professional distinction. \n"If you devote yourself to a task, do it for the sake of the task, not for the personal gain or fame," he said. "That's when you can look back at what you've achieved and be happy that you've done something important. "\nWhile the full impact of these findings remains to be seen, Estelle said he does not consider this a stopping point for research on plant growth. \n"It's an important landmark," he said. "But there are still many questions that remain to be answered"