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The transgenic MS1 plants do not produce viable pollen grains and
cannot self-pollinate. In order to restore fertility in the hybrid
progeny, line MS1 must be pollinated by a modified plant containing
a fertility restorer gene. The resultant hybrid seed derived from
the cross generates hybrid plants that produce pollen and are
completely fertile.
The male-sterile trait was introduced in MS1 by inserting the
barnase gene, isolated from Bacillus amyloliquefaciens, a common
soil bacterium that is frequently used as a source for industrial
enzymes. The barnase gene encodes for a ribonuclease enzyme (RNAse)
that is expressed only in the tapetum cells of the pollen sac
during anther development. The RNAse affects RNA production,
disrupting normal cell functioning and arresting early anther
development, thus leading to male sterility.
MS1 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.
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