In 1982, the first transgenic plants were produced in tobacco plants (Nicotiana tabacum) which expressed antibiotic resistance.  A gene resistant to PPT (L-phosphinothricin), an active ingredient of herbicide ‘Basta’, was isolated from Medicago sativa. It inhibits the enzyme GS (glutamine synthase) which is involved in ammonia assimilation. This gene resistant to PPT was incorporated into tobacco, as a result of which transgenic tobacco was produced which was resistant to PPT.

Source: ForumIAS