By Fred Miller, Science Editor

Arkansas Agricultural Experiment Station

March 20, 2003

fmiller@uark.edu

A key gene that controls tolerance to drought, salt and cold in rice has been identified and studied 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 cereal crops.   It was one of more than 200 rice genes isolated by Yang and his research group that are associated with disease resistance and stress tolerance. Understanding exactly what each of these genes does requires subjecting them one-by-one to molecular, biochemical, genetic and genomic analysis. "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 leading journal of plant biology by the American Society of Plant Biologists.

Yinong Yang, UA molecular biologist, is studying the functions of a gene that triggers stress tolerance in rice. In experimental transgenic rice plants --- some with the gene suppressed and others with the gene over-expressed --- he is measuring the plants' responses to drought, salt and cold stresses.

MAPK5 in rice gene encodes kinase, a protein that regulates plant defense response to various environmental stresses. "This gene is activated in rice plants by abiotic stress, including drought, salinity and cold," Yang said. "It is also induced by biotic stresses such as fungal and bacterial pathogens."

 

He said at least five research groups in Japan, Taiwan and the U.S. have isolated the same gene, but only Yang's group has identified its biological function with transgenic analysis.

 

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 had a higher survival rate under drought, salt and cold conditions," Yang said. "The suppressed plants tended to die under the same levels of stress."

 

Yang said their tests demonstrated that MAPK5 is a positive regulatory gene for abiotic stress tolerance in rice plants. "Regulatory genes are the 'white collar' workers in biology," he said. "They pass along cellular signals that turn 'blue collar' structural genes on or off.

 

"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.