Tomato line 8338 was developed by introducing into the genome of a
processing tomato cultivar UC82B a gene for
1-amino-cyclopropane-1-carboxylic acid deaminase (ACCd) derived
from a nonpathogenic soil bacterium (Pseudomonas chlororaphis). In
the plant, this enzyme catalyzes metabolism of
1-amino-cyclopropane-1-arboxylic acid (ACC), an essential precursor
for the biosynthesis of the plant ripening hormone ethylene.
The initiation and progression of tomato fruit ripening depends on
increased levels of ethylene. In line 8338, ACC is sufficiently
reduced in detached fruit so that ethylene becomes limiting and the
ripening process is delayed. Line 8338 has also been transformed
with the nptII gene derived from Escherichia coli that encodes the
enzyme NPTII. NPTII confers resistance to certain antibiotics, such
as kanamycin, that are used to select transformed cells.