Rice line LLRICE62 was genetically 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 these rice lines is the result of
introducing a gene encoding the enzyme
phosphinothricin-N-acetyltransferase (PAT) isolated from the common
aerobic soil actinomycete, Streptomyces hygroscopicus, the same
organism from which glufosinate was originally isolated. 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. The PAT encoding gene (bar) was introduced
into the rice genome by direct gene delivery transformation, and
the resulting rice lines displayed field tolerance to
phosphinothricin-containing herbicides.
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