Unmasked. The standard plant (top) reveals exotic new forms if HSP90 is restricted.

Mustard Mutants Revealed

The common mustard plant (Arabidopsis thaliana) may look drab, but a study shows it has a surprising ability to break out into new forms--some of them weird and exotic--when it is under stress. The researchers suggest that this ability may play an important role in evolution in a variety of organisms, possibly allowing organisms to store alternative survival strategies and express them only during environmental extremes.

Previous experiments showed that reducing a protein called heat shock protein 90 (HSP90) in developing fruit flies produces dramatic changes--such as misshapen wings and abnormal eyes. This suggested that the fruit fly genome harbors many developmental mutations that are normally suppressed by HSP90, which stabilizes other cellular proteins. Its moderating effect is transitory, however. During periods of extreme stress, HSP90 protection fails. Researchers proposed that HSP90 allows the flies to store many genetic mutations in normal times but express them only in tough times.

To see how widespread the phenomenon might be, Christine Queitsch, a molecular biologist, and her colleagues at the University of Chicago, tried a similar experiment in an organism quite unlike the fruit fly. They treated Arabidopsis seedlings with chemicals that inhibit the function of HSP90 genes and produced a stunning array of developmental changes. They found, for example, that leaves that are normally held at right angles come out in a whirl, the plant's gentle green hue turns dark, and roots reach for the sky. The team reports its findings in a 13 May advanced online publication in Nature.

The study is "excellent," and the analysis of this genetic puzzle is "really super-interesting," says botanist John Archibald of the University of British Columbia in Vancouver, Canada. Next, the team hopes to conduct experiments to investigate whether the variation caused by changing HSP90 levels could play a role in evolution, Queitsch says. They also plan to use HSP90 to bring out hidden variations that could be valuable in agriculture--looking for ways to modify plants without controversial germ line alterations.

Related sites
Senior author Susan Lindquist's site
Arabinet--Arabidopsis links