process, in which the damaged DNA might then be replaced by the similar, but not iden-
tical, template introduced into the cell (Fig. 16.4). As with many biotechnologies, the
relatively rich field of biomedical science often spills over into plant biology. A number
of researchers agree that the idea seems promising, but this technology is relatively new
and only time tell whether it will be effective for engineering crop plants. If it lives up
to promise, there will be many applications for zinc-finger nucleases, such as correcting
mutant sequences in plants (“plant gene therapy”), engineering herbicide resistance by
point mutations, and applications similar to those proposed for site-specific recombination
systems indicated above (Wright et al. 2005).
16.4 The Future of Food (and Fuel and Pharmaceuticals)
One of the unexpected developments in plant biotechnology has been the concern of food
companies about accidental transgene transgenic product “contamination” in foods—called
adventitious presenceoradmixture. These companies often employ biotechnology in their
own right, but are concerned about potential marketing problems and food safety issues,
especially in export markets. For example, a beer company was not happy that transgenic
rice for human pharmaceuticals was being grown in the same state that was home to its rice
fields—they were worried about admixture that might complicate its product. And there was
concern among farmers that admixture might harm export markets to “no GMO” countries.
While industry and farmers are generally pro-innovation, this was a case in which they
were more worried about potential harmful occurrence that might hamper economics of
existing products.
What does the admixture problem mean for the future of plant biotechnology? It has
been argued that using biotechnology to modify food plants for pharmaceuticals and
now bioenergy production must take into consideration food uses first. For example, engin-
eering a soybean for a better diesel fuel would have to first consider soybean oil for
Figure 16.4.A promising approach for homologous gene replacement. Site-directed DNA cleavage
by a zinc finger nuclease, with each zinc finger (triangles) recognizing a 3-nucleotide sequence, pro-
motes DNA repair that leads to higher rate of homologous recombination. Example shows replace-
ment of gene 2 by gene 2^0.
364 THE FUTURE OF PLANT BIOTECHNOLOGY