Transgenic tomatoes altered with a marker gene construct showed
significant changes in morphological and physiological characteristics.
Tomato (Lycopersicon esculentum mill.).
GUS (uidA) gene for the synthesis of the enzyme beta-glucuronidase
(GUS); GUS is a marker gene and was fused to the cauliflower mosaic
virus (CaMV-35S) promoter so that it would be expressed in all tissues
of the plant. The construct was inserted into tomato tissue via
Goal of This Study:
Investigate whether transgenic tomatoes carrying gene constructs with
a marker gene, which would not be expected to change a plant's
morphology and physiology, show any differences from the parent variety
out of which the transgenic tomatoes were developed. Three transgenic
tomato lines were compared with the parent variety: one line that showed
high expression of GUS; a second line where GUS expression was silenced;
and a third line that had lost the GUS gene through outcrossing so that
it was genetically equivalent to the unmanipulated controls but had been
subjected to the genetic manipulation and to tissue culture regeneration.
Results of This Study:
In 11 of 25 morphological and physiological characteristics that were
subjected to statistical analysis, the unmanipulated parent variety
differed significantly from all three genetically engineered lines. With
respect to an additional seven characteristics, the parent variety
differed significantly from one or two of the genetically engineered
lines. The largest number of differences (15) were found between the
parent variety and the line with the silenced GUS gene. Surprisingly,
the line that had lost the gene construct through outcrossing
differed from the parent variety just as much as the line that had
high expression of GUS. The transgenic lines were more similar to each
other morphologically and physiologically than they were to the parent
variety. The characteristics in which the parent variety differed from
one or more of the transgenic lines included plant height, thickness of
the main shoot, leaf shape and size, leaf color, number and organization
of fruit branches (inflorescence branching pattern), and fruit number
For example, in comparison to the parent variety, all three transgenic lines
(except where noted) had:
On average two fewer fruit-bearing branches per plant, but in
proportion more subdivided fruit-bearing branches (changed inflorescence
architecture) and two fruits more per branch.
On each inflorescence, the first fruit that formed originated at a further
distance from the main stem, which might increase the likelihood of the
fruit-bearing branches tearing and breaking off the main stem.
A significantly larger number of tomatoes with a green collar around the
upper part of the tomato - an area of thickened tissue that stays green
(a commercially undesirable trait).
Significantly lower total acid content in fruits of two of the three
Larger and darker green leaves that were more rolled in at the margins
than those of the parent variety.
Exactly how the genetic manipulation was related to these changes in
morphology and physiology is unclear. Since both the line with the
silenced marker gene and the line that had lost the construct differed
in many features from the parent variety and were more similar in those
features to the line that expressed the marker gene, the changes cannot
be due solely to the expression of the marker gene but rather to the
whole process of genetic transformation.
The fact that three different transgenic lines could be chosen for
investigation in this study already indicates that the production of
the transgenic lines involved unintended effects. The goal had been to
create transgenic tomatoes with high expression of the GUS gene. The lines
showed variable expression of the GUS gene, and one high-expressing line
was used in this study. The line with the silenced GUS gene represents,
of course, an unintended effect.
Schätzl, A. (2007). "Nicht Beabsichtigte Effekte von Gentechnischen
Veränderungen bei Tomaten (Lycopersicon esculentum Mill.)."
[Unintended Effects of Genetic Modifications of Tomatoes], Diploma Thesis,
Fachhochschule Weihenstephan, Germany.
This study was a thesis research project.
Not on the market as of 2008.
Copyright 2008 The Nature