Transgenic RF2 plants contain the barstar gene, isolated from
Bacillus amyloliquefaciens. The barstar gene codes for a
ribonuclease inhibitor (barstar enzyme) expressed only in the
tapetum cells of the pollen sac during anther development. The
ribonuclease inhibitor (barstar enzyme) inhibits barnase RNAse
expressed by lines engineered to be male steril and together, the
RNAse and the ribonuclease inhibitor form a very stable one-to-one
complex, in which the RNAse is inactivated. As a result, when
pollen from the restorer line RF2 is crossed to a male sterile
line, the resultant progeny express the RNAse inhibitor in the
tapetum cells of the anthers, allowing hybrid plants to develop
normal anthers and restoring fertility.
RF2 was also engineered to express tolerance to glufosinate
ammonium, the active ingredient in phosphinothricin herbicides
(Basta®, Rely®, Finale®, and Liberty®). Glufosinate chemically
resembles the amino acid glutamate and acts to inhibit an enzyme,
called glutamine synthetase, which is involved in the synthesis of
glutamine. Essentially, glufosinate acts enough like glutamate, the
molecule used by glutamine synthetase to make glutamine, that it
blocks the enzyme's usual activity. Glutamine synthetase is also
involved in ammonia detoxification. The action of glufosinate
results in reduced glutamine levels and a corresponding increase in
concentrations of ammonia in plant tissues, leading to cell
membrane disruption and cessation of photosynthesis resulting in
plant withering and death.
Glufosinate tolerance in this canola line was the result of
introducing a gene encoding the enzyme
phosphinothricin-N-acetyltransferase (PAT) isolated from the common
aerobic soil actinomycete, Streptomyces hygroscopicus. The PAT
enzyme catalyzes the acetylation of phosphinothricin, detoxifying
it into an inactive compound. The PAT enzyme is not known to have
any toxic properties.
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