Bob Cohen asked: "What are Agrobacterium plasmids?"
answer:
For several years now the plant parasite Agrobacterium tumefaciens (a
bacterium related to the nitrogen-fixing bacterial symbiote Rhizobium) has
been used to genetically engineer plants. Agrobacterium carries an
extrachromosomal piece of DNA (a plasmid) that it injects into plant cells at
wound sites. This plasmid DNA makes its way to the chromosomes of the
infected plant cells and integrates into the host cellular DNA. From this
vantage the inserted DNA directs the plant cell to do two things: 1) divide
without growth control ("tume"-faciens" for tumour promoting) and 2) make
nitrogen-containing compounds such as nopaline and other things that the
bacteria can feed upon.
Basically, the bacteria induces the plant to make it a home and also to
synthesize its food. Plant geneticists have taken advantage of this natural
genetic engineering property of A. tumefaciens plasmids by 1) removing the
tumour-inducing qualities of the plasmids, 2) removing the nopaline synthetase
and other "bacterial" genes and have 3) retained in the plasmid the ability to
insert into DNA. New genes of interest to the invesigator are put in place of
the "bad" genes. In the processes derived to date, the plasmids are directed
to carry in DNA of interest to the researcher or plant breeder. Because many
plant cells are pluripotential in that they can be induced with appropriate
hormones to regenerate into whole plants, cells infected with recombinant
Agrobacterium plasmids can be made and propagated in "germ-line" (carried in
pollen, ovum, or seed) contexts.
My interest is in "transforming" Drosera cells with DNA from other plant
species. Many genes have been cloned from other plants that control the
differentiation potential of the plant (elongated stems, whorl formation,
flower color etc.). Many of these genes have been inserted into Agrobacterium
plasmids and shown to change the size/shape/character of the infected plant--
sometimes quite dramatically. Most interesting are those genes that effect
the homeotic and pattern formation of plant growth. This involves such things
as branching, leaf shape, leaf placement etc.
A simple example of a likely naturally occurring homeotic mutations in CP
would be the D. binata to D. dichotoma to D. multifida series. D. binata is
likely to be the only obvious living ancestor of the group. There probably
was capensis-like ancestor to binata in which homeotic mutation in a gene
responsible for leaf shape induced a bifurcation in the leaf development
process. "strong" alleles (mutants) of this gene induce the dichotoma
phenotype. "stronger" alleles give multifida etc. until one reaches multifida
extrema. The original selection of the capensis-like to binata transformation
basically set the stage (I hypothesize) for further homeotic mutations along
the multifida path. It's possible that we can induce similar dramatic changes
in Drosera shape with appropriate engineering.
Anyone, that's a long discourse on where my interests with Drosera lay. I
think some interesting and novel shapes can be generated from the basic
species without too much ado. Agrobacterium plasmids are the means to such an
end.
Garry Nolan