<p style="text-align: justify;">Maize line MS6 (tradename InVigor&reg;) was developed to provide a reliable hybridization system based on nuclear male sterility. The transgenic line was produced by genetically engineering plants to be male sterile and tolerant to the herbicide glufosinate ammonium, where herbicide tolerance was used as a selectable marker to identify the male sterile plants. These transformed maize lines contain the barnase gene for male sterility, isolated from <i>Bacillus amyloliquefaciens</i>, 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.</p>

<p style="text-align: justify;">The male sterile maize line MS6 also contained the <i>bar</i> gene isolated from the common soil microorganism <i>Streptomyces hygroscopicus</i>, for use as a selectable marker. The <i>bar</i> gene encodes a phosphinothricin acetyl transferase (PAT) enzyme, which, when introduced into a plant cell, confers tolerance to the herbicide glufosinate ammonium. The herbicide tolerance trait was introduced into the maize line as a selectable marker to identify transformed plants during tissue culture regeneration, and as a field selection method to identify the male sterile lines at any growth stage. Under field conditions, plants that were not male-sterile could be eliminated by application of the herbicide glufosinate ammonium. The novel hybrid system provided an efficient and effective way to identify male-sterile plants for use in hybrid seed production.</p>

<p style="text-align: justify;">Glufosinate ammonium is the active ingredient in phosphinothricin herbicides (Basta, Rely, Finale, and Liberty) and acts by inhibiting the plant enzyme glutamine synthetase, a key enzyme in plants that detoxifies ammonia by incorporating it into glutamine. Inhibition of this enzyme leads to an accumulation of ammonia in the plant tissues, which kills the plant within hours of application. PAT catalyses the acetylation of the herbicide phosphinothricin and thus detoxifies glufosinate ammonium into an inactive compound.</p>

<p style="text-align: justify;">In the United States, the male-sterile line MS3 was designated as the antecedent organism for MS6 for the purposes of conducting the environmental safety assessment. Maize lines MS3 and MS6 were genetically modified using the same transformation technique and the same genetic elements. Based on the similarity between MS6 and the antecedent organism MS3, and on an analysis of scientific data and field tests of MS6, the maize line MS6 was judged not to have any characteristics that would pose a greater impact on the environment or non-target organisms.</p>

<p style="text-align: justify;">For additional information related to either the environmental or food safety assessment of the antecedent organism, MS3, the reader is referred to the description for that product.</p>
