TOBACCO plants that switch on a gene in the presence of ethanol could lead to
flowers that bloom on demand or crops that produce pesticides only when under
attack.
When biotechnologists insert foreign genes into a crop plant to make it
resistant to certain pests or change its growing patterns, the plant normally
churns out the genes鈥� products for the rest of its life. In the laboratory,
however, researchers can control the timing of gene expression using promoter
genes, which switch on certain other genes in response to compounds such as
tetracycline or elements such as copper.
Brian Tomsett of the University of Liverpool was using such chemical switches
to study gene expression in plants. But he was aware that they are not perfect.
For instance, they don鈥檛 allow you to switch a gene off entirely; the plants
always make a small amount of the protein, even in the absence of the promoter.
This makes it impossible to study toxic or lethal genes, for example.
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So Tomsett set out to look for a better gene control system, and he has found
one鈥攅thanol. It could also be used on farmers鈥� crops, as unlike
tetracycline or copper, it could be sprayed over whole fields.
Tomsett knew that a filamentous fungus called Aspergillus nidulans
has a promoter gene that is activated by ethanol. His team altered this genetic
system slightly so that it would work in tobacco, then delivered the genes using
a bacterium that integrates its DNA into the plant鈥檚 chromosomes.
The team showed that the tobacco plants switched on a certain protein only
when the roots or leaves were sprayed with a 0.1 per cent ethanol solution. They
also used ethanol to trigger late production of a highly toxic protein,
cytosolic invertase, after the plants鈥� leaves had developed normally. Their
findings appear in this month鈥檚 Nature Biotechnology (vol 16, p
177).
If ethanol doesn鈥檛 harm the root growth of plants, this could be the first
gene expression control that would be practical for widespread use in
agriculture. 鈥淲e鈥檙e talking about levels that are much lower than your alcoholic
beverage,鈥� says Tomsett, who adds that some agricultural chemicals already use
ethanol as a solvent. 鈥淎s far as I鈥檓 aware, this is probably the only system
around that has this potential.鈥�
Other experts agree. 鈥淚t looks like a really interesting possibility,鈥� says
biologist John Benedict of Texas A&M University in Corpus Christi. 鈥淎s
geneticists continue to search for appropriate promoters, they鈥檒l find more
things like this.鈥�
Compounds that control the timing of gene expression would allow farmers to
regulate the flowering and development of their transgenic crops to fit in with
the weather. It would also mean that plants could be made to express pesticide
genes, like that of Bacillus thuringiensis , only when they were under
major attack by insects. This would avoid the constant exposure that allows
pests to become resistant.
While engineering a response to ethanol is a big step towards that goal,
Benedict points out that agricultural companies would probably want to engineer
their own proprietary compounds to activate promoters specific to their own
plant varieties. Farmers would have to buy these rather than using something
generic like ethanol.