UV Glare Gets Genes Jumping

A thinning ozone layer may ultimately send maverick DNA segments called transposons jumping throughout the genome of corn plants, according to a report in today's Nature. These nomads could lead to a flood of mutations, the author says.

Transposons are snippets of DNA that can clip themselves out of the genome and reinsert themselves at random in another gene. Scientists have known for several years that a bombardment of ultraviolet light, particularly long wavelength UV, can activate corn transposons. But no one had studied whether UV light at more ambient levels might also set transposons in motion.

So corn geneticist Virginia Walbot of Stanford University examined the effects of short wavelength UV irradiation on corn plants growing on an experimental plot near Stanford. She collected pollen and irradiated it in a lab for 3 minutes with UV light, simulating the amount of UV that can reach the Earth's surface in Patagonia and other regions in the southern hemisphere under the seasonal ozone hole. Because pollen only remains viable for 30 minutes, Walbot then says she "ran like the devil" back to the field to use the irradiated pollen to fertilize plants in an adjacent plot.

In the resulting ears of corn, Walbot measured the amount of transposon migration by looking for reddish spots on the kernels, an indication that a transposon had inserted itself into a color-producing gene. Seven of the 19 ears and 6.2% of the kernels overall showed spotting; this occurs in less than a fraction of a percent of normal plants. Such heightened transposon activity--if it is occurring in plants down under--could be a significant consequence of ozone depletion, Walbot says.

The specter of active transposons "is certainly something to be concerned about, especially in wild plants," says agronomist Patrick Schnable of Iowa State University in Ames. On the other hand, he says, the findings could help researchers who are using transposons to deliberately insert beneficial genes into plants. "One could use UV to increase transmission rates," he says.