"Die and let live" strategy dramatically boosts drought resistance in rice: study

China and U.S. researchers said Monday that engineering rice and the model plant Arabidopsis to produce high levels of a protein known as PYL9 can dramatically increase their drought tolerance.

Under severe drought conditions, the transgenic plants triggered the death of their old leaves -- a process known as senescence -- to conserve resources for seeds and buds, a survival strategy some plant scientists refer to as "die and let live," they said.

The study, published in the U.S. journal Proceedings of the National Academy of Sciences, offers insights into the drought survival mechanisms of plants and presents a possible means of protecting crops from severe drought stress.

"This study shows that controlled senescence is good for plants under drought conditions," said first author Yang Zhao of the Shanghai Center for Plant Stress Biology in China.

"This combination of death and life is similar to a triage strategy. If old leaves die, then the buds and small leaves might gain life," said Zhao, who is also a research assistant in the Jian-Kang Zhu lab in the Purdue University.

Plants' drought responses are controlled by a hormone known as abscisic acid (ABA), which regulates growth and development and directs plants' reaction to stress.

Zhao and his fellow researchers found that altering Arabidopsis and rice to overexpress PYL9 made them highly sensitive to ABA, enabling them to better withstand severe drought stress and causing older leaves to yellow sooner compared with the plants' wild type counterparts.

They found PYL9 transgenic rice had a 50 percent survival rate after a two-week drought compared with 10 percent survival in wild type rice.

Zhao, however, did not test the yield and quality of the transgenic plants.

"We still can't really solve the problem of drought," he said. "But we can make it better. In extreme drought conditions, even a bad yield would be better than nothing in terms of preserving human life."

The transgenes did not affect plant growth and development under normal conditions, which suggests that they could be used to improve crop drought tolerance.

"This study not only illuminates the function of PYL9 in stress-induced leaf senescence but also demonstrates a great potential for using PYL9 to improve plant drought resistance," Jian-Kang Zhu, distinguished professor of plant biology and the study's principal investigator, said in a statement.

Unexpectedly, when transgenic plants were treated with ABA under normal conditions, the old leaves started to wilt, even though the plants received enough water.

This suggests that the plants had blocked their old leaves' access to water, preferentially driving water to developing tissues instead, they added. Endit