A key gene that controls tolerance to drought, salt and cold in rice has been identified and tested by researchers at the University of Arkansas Division of Agriculture.

Understanding the gene's function may be important to breeders developing rice varieties that can tolerate drought and salt in areas of eastern Arkansas where ground water sources are declining in quantity and quality, said Yinong Yang, molecular biologist for the Arkansas Agricultural Experiment Station.

Yang said the gene, designated “mitogen-activated protein kinase 5,” or MAPK5, also may be used to improve stress tolerance in other crops.

It was one of more than 200 rice genes isolated by Yang and his research group that are involved in disease resistance and stress tolerance. Understanding exactly what each of these genes does requires studying them one-by-one.

“We can't study all of them in detail, so we selected the genes that seemed most important and started with MAPK5,” Yang said.

An article by Yang and research associate Lizhong Xiong, describing their detailed study of the gene, has been published in the March issue of The Plant Cell, the journal of the American Society of Plant Biologists.

MAPK5 regulates the production of kinase, a protein that regulates plant response to abiotic stress. These include stresses induced by non-living sources, such as lack of water or excess salt or cold. To a lesser degree, MAPK5 seems to play a role in interrupting biotic stresses caused by diseases.

“This gene is induced by abiotic stress,” Yang said, “but it is also activated by blast and some other rice diseases.”

To study the gene's function, Yang and Xiong genetically modified rice plants in two ways. In some of the plants, MAPK5 was suppressed so that it would remain dormant under stress. In other plants, the gene was over-expressed, meaning that it would respond faster or stronger to stress. The results were compared to control plants in which the gene was not modified.

“The over-expressed plants survived drought and cold,” Yang said. “The suppressed plants tended to die under stress.”

Yang said their tests demonstrated that MAPK5 is a key regulatory gene for plant defense.

“Regulatory genes are the white collar workers in biology,” he said. “They're the managers that turn ‘blue collar’ structure genes on or off.”

Structure genes provide the labor force that sustains life in the plant. “Regulatory genes and structure genes work together to control plant function,” Yang said. “Some genes cross the lines to do the work of both types.”

Yang's and Xiong's article in The Plant Cell can be read online at www.plantcell.org/cgi/content/full/15/3/745.


Fred Miller is science editor for the Arkansas Agricultural Experiment Station. e-mail: fmiller@uark.edu.