Smart crops

farmers can now grow tobacco plants on demand or crops that produce pesticides only when under attack. Scientists have found a gene that can be switched on in tobacco plants or other crops in the presence of ethanol to get the desired result.

When foreign genes are inserted into a crop to make it resistant to certain pests or to change its growing patterns, the plant normally churns out the genes' products for the rest of its life. In the laboratory, however, researchers can control the timing of the gene expression with the help of promoter genes, that switch on certain other genes in response to compounds such as tetracycline or elements such as copper (New Scientist, Vol 157, No 2120).

Brian Tomsett of the University of Liverpool, uk, was using such chemical switches to study gene expression in plants.But they did not allow a gene to be switched off entirely as the plant always made a small amount of protein, even in the absence of the promoter. This made it impossible to study toxic or lethal genes.

Tomsett has found a better gene control system called ethanol. This system could also be used on farmers' crops and could be sprayed over whole fields, unlike tetracycline or copper.

A filamentous fungus called Aspergillus nidulaus has a promoter gene that is activated by ethanol. This genetic system was slightly altered by Tomsetts' team so that it could work in tobacco. Then the genes were delivered into the plants chromosomes, using a bacterium that integrates its dna.

The team showed that a certain protein was switched on by the tobacco plants only when the roots or leaves were sprayed with a 0.1 per cent ethanol solution. Ethanol was also used to trigger late production of highly toxic protein, cytosolic invertase, after the plants' leaves had developed normally. If ethanol does not harm the root growth of the plants, this could be the first gene expression control that would be practical for widespread use in agriculture.

According to Tomsett, the levels were much lower than alcoholic beverages. Some agricultural chemicals are already using ethanol as a solvent, he added.

Compounds that can control the timing of gene expression would help farmers to regulate the flowering and development of their transgenic crops to fit in with the weather. Plants could also be made to express pesticide genes, like that of Bacillus thuringiensis, only when they are under major attacks by insects. This would avoid the constant exposure that allows pests to become persistent.