Scientists reveal secrets of drought resistance

A Mysterious Hormone

When drought-tolerant plants detect dry conditions, they synthesize abscisic acid, which causes changes from root tips to leaves and flowers. Plants under the influence of this hormone begin to conserve water. Their seeds lie dormant in the ground. Their leaves close microscopic pores to stop water loss. They slow their own growth, and they signal numerous genetic changes, reprogramming themselves to accomplish their single most pressing goal - survival.

"Abscisic acid triggers an array of plant drought-tolerance mechanisms," said co-investigator Julian Schroeder of UC San Diego.

The hormone abscisic acid was discovered in the early 1960s, and plant biologists have known for decades that it plays this crucial role in keeping plants alive during drought. Despite this fact, says Getzoff, who is a professor in the Department of Molecular Biology and The Skaggs Institute for Chemical Biology at Scripps Research, nobody has understood how the hormone functions.

"That has been pretty mysterious," Getzoff says, "yet solving this mystery is key to controlling drought responses to protect plants." Collaborating closely with Schroeder and his lab, Getzoff and her group decided to try to figure out exactly how PYR1 was involved in drought resistance by looking at PYR1 and abscisic acid molecules on the micro-and nano-scales.

... The research showed that two copies of PYR1 fit snugly together in plant cells. There, they are targeted by abscisic acid. Each copy of the PYR1 molecule has an internal open space like the inside of a tin can, and when a hormone molecule comes along, it fits neatly into one of the two spaces. This induces part of the PYR1 protein that the team calls the "lid" to close. Further structural changes to other parts of the PYR1 molecule initiate interactions with other proteins thus triggering plant processes for resisting drought.

Tantalizing Possibilities

The structure may reveal new ways of improving drought tolerance in plants, notes Getzoff. Such improvements would be a boon for agriculture, which is the single largest use for water in most of the world, consuming up to 90 percent of available water in some of the hottest and most arid parts of the world, which are often prone to drought.

One possible way to translate this research to agricultural products, says Getzoff, would be to design chemicals to mimic the action of abscisic acid. Such chemicals would then be sprayed on crops to protect them in the face of looming drought. The hormone itself would not work for this purpose because industrial-scale production of abscisic acid would be very expensive and sunlight can convert it into an inactive form.

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