Contact Information Jian-Kang Zhu 520-626-2229 jkzhu@ag.arizona.edu Related Link(s) The Zhu Lab

Scientists at the University of Arizona have discovered a critical cold-tolerance gene in Arabidopsis, a cruciferous plant related to cabbage and broccoli. As published in the April 15 issue of "Genes & Development," the identification of ICE1 by Jian-Kang Zhu and his colleagues holds promising implications for the improvement of cold tolerance in agriculturally important crops.

Cold is a major factor affecting crop yield in temperate climates, with the farming industry losing billions of dollars each year to freezing temperatures. Researchers have focused on ways to improve crop tolerance to cold and/or freezing temperatures, to both increase productivity and to broaden the geographic range for crops.

In 1988, scientists identified the Arabidopsis CBF (C-repeat binding factor) family of genetic transcription (coding) factors. These CBF proteins regulate the expression of cold- responsive genes in Arabidopsis, which enable the plant to acclimate to, and survive in, cold temperatures.

Zhu, a professor of plant sciences in the UA College of Agriculture and Life Sciences, and his colleagues have discovered a key transcriptional regulator of those CBF genes ? a marked advance in the research effort to understand and ultimately improve cold tolerance in plants.

To identify genes that act upon CBF genes and affect cold tolerance in plants, Zhu and his team carried out a genetic screen with Arabidopsis plants that were genetically engineered to glow in the cold. They inserted a modified gene containing the firefly enzyme luciferase into the Arabidopsis genome, to generate plants that glow under cold stress. These cold-responsive bioluminescent plants were then induced to mutate, and plants that no longer glowed in cold temperatures were selected.

"If a plant is not glowing, or glowing too brightly, we know a particular gene is involved," Zhu says.

This process is painstaking and yields results slowly, but works much faster than traditional breeding methods, which can take years as different plant generations are grown out and evaluated. Since the luciferase enzyme induces a glow too weak to be seen by the naked eye, Zhu uses a camera to view the steady glow.

One particularly striking mutant exhibited ten times less luminescence after 12 hours at 0ºC than the wild-type bioluminescent plants.

Zhu and his colleagues cloned the gene that had been mutated in this plant, and named it ICE1 (inducer of CBF expression). Further research by the group revealed that ICE1 is also a transcription factor: During periods of cold stress, ICE1 binds to and turns on the CBF3 gene, which, in turn, induces the expression of cold-responsive genes.

Using microarray analysis, the researchers demonstrated that in ICE1-mutant plants, more than 70 percent of cold-responsive genes are misregulated, causing the plants to exhibit severely reduced cold tolerance.

The team also demonstrated that the increased expression of ICE1 in Arabidopsis plants leads to increased cold tolerance.

This result is expected to garner significant attention from the agricultural community, as the transgenic expression of ICE1 in domesticated, cold-sensitive crops - like soybeans, tomatoes, potatoes, rice and barley - may provide a new way to increase the ability of such plants to survive in the cold.

"The significance of our findings on ICE1 may be two-fold," Zhu says. "It is likely useful for the genetic improvement of plant freezing tolerance, and the identification of ICE1 takes us one step closer to address the question how cold signals are sensed and transduced."

Contact Jian-Kang Zhu at (520) 626-2229, jkzhu@ag.arizona.edu
His lab web page is at http://ag.arizona.edu/pls/zhulab

The article, ?ICE1: a regulator of cold-induced transcriptome and freezing tolerance in Arabidopsis? is online at http://www.genesdev.org/cgi/reprint/U-10775Rv1.pdf