Integrated Environmental Biotechnology 263Once the T-DNA is integrated into the host plant cell genome, these genes may
be expressed leading to the establishment of crown gall disease.Agrobacterium
tumefaciensthen contains a very effective delivery system for bacterial genes into
a plant cell; a natural process which is utilised by genetic engineers to introduce
‘foreign’ genes into plants as described in Chapter 9.
Cauliflower mosaic virus
The study of plant viruses has lagged behind that of animal or bacterial viruses
due to difficulties in their culture and isolation. While some may be grown in
isolated plant cultures, many require the whole plant and some also require an
insect intermediate either simply as a means of transmission between plants, or
additionally as a site for virus replication. Transfer of viruses between plants by
insects is the most common means, especially by insects which penetrate and
suck plants, aphids being an example. However, there are other routes such as
transfer by plant parts through infected seed, tubers or pollen. Other agents are
those able to penetrate plant tissue which include soil nematodes and parasitic
fungi. The genetic material of most plant viruses is RNA, either double or single
stranded. Caulimovirus, or more commonly, Cauliflower Mosaic Virus is unusual
in having a DNA genome. This has proven very fortuitous for genetic engineer-
ing as it possesses two very strong constitutive promoters, the 35S and the 19S;
for an explanation of the term ‘promoter’ see Chapter 2. Since these promoters
originated from a plant virus, any construct made with the intention of expressing
the ‘foreign’ gene in a plant has a higher likelihood of the signals being recog-
nised by the transcription machinery of the plant than if they were derived from,
for example, bacterial promoters. These promoters have proved very successful
and particularly the 35S, often designated in publications as ‘35S CaMV’, has
become almost the archetype promoter to drive the expression of ‘foreign’ genes
in plants. Examples of these are given in Chapter 9. However, while genetic
engineering, building on these and other natural abilities, may permit novel tech-
nological approaches to emerge, which have major potential relevance to the
environmental sphere, currently they are of somewhat limited commercial appli-
cation. At present, there seems to be much more scope, at least in practical terms,
for the bundling of existing technologies into treatment trains, or the re-entry of
post-processed biological material into the chain of commercial utility.
Closing Remarks
Biotechnological integration often permits a number of key environmental con-
cerns to benefit. The use of phytotechnology using whole organism systems to
clean effluents has been discussed in an earlier chapter. Recently, waste biomass
from the brewing industry, which normally represents a disposal problem to the
industry, was found to have unexpected abilities to remove a number of common