UMD-Led Team Cracks 60-Year Code Through Discovery of Enzyme that Optimizes Plant Life

A UMD-led team of researchers has answered a question that scientists have been pondering for 60 years: Exactly how do plants turn off the action of the vital plant growth hormone auxin?

It turns out the answer is an enzyme now identified and characterized for the first time by scientists from the University of Maryland’s College of Agriculture and Natural Resources (AGNR) and from the Agricultural Research and Development Center of The Ohio State University, The researchers published their findings this week in a paper in the Proceedings of the National Academy of Sciences (PNAS).

Auxin is the determining factor in how a plant grows, develops and responds to the environment.  Scientists have long known the processes of synthesis and breakdown by which plants optimally regulate the amount and effects of the hormone. However, what has been unknown until now is what enzyme or enzymes catalyze the breakdown, or oxidation, of auxin. 

Led by UMD’s Jun Zhang, a recent AGNR PhD graduate from plant science and landscape architecture, and Wendy Peer, Ph.D., an assistant professor in AGNR’s department of environmental science and technology, the research team used a combination of biochemistry, genetics, molecular biology, physiology and metabolomics (the study of small molecules found in plant cells and fluids) to show the primary breakdown enzyme is dioxygenase of auxin oxidation (DAO).

This is promising new knowledge for horticulturalists and farmers. Controlling when and where and how much auxin is active via DAO could lead to new ways to improve plant growth and productivity. This could have wide-ranging effects in crops from improving drought stress to increasing biomass. Benefits for the nursery industry include improved rooting of cuttings from tomatoes to trees.

Zhang and Peer and colleagues used a small flowering plant or weed called Arabidopsis as their plant model for this research. In this plant, they were able to showcase the inactivation of auxin by way of DAO, facilitating the process of that turns auxin off. Prior to these findings, the enzymes that catalyze this process and how they work to maintain hormone balance and influence plant growth only had been hinted at in studies of apple trees and rice plants.

“We are excited about solving this puzzle at last,” says Peer. “Our goal is to address the world food crisis in the face of climate change. Understanding and then controlling the activity of this essential plant hormone is one of the keys to doing just that.”

Their paper in the Proceedings of the National Academy of Sciences (PNAS) is titled “DAO1 catalyzes temporal and tissue-specific oxidative inactivation of auxin in Arabidopsis thaliana.”

This is one of three papers published together on this subject with UMD and Ohio State demonstrating the biochemistry, genetics, physiology, and metabolomics of DAO; Umeå Plant Science Centre, Sweden, showing auxin metabolomics, genetics and physiology; and the University of Nottingham, UK, modelling DAO functions in auxin homeostasis in roots.

Image is by INRA and Jean Weber Under Creative Commons License. Link (link is external) to original photo in Flickr Commons.