Suppression of DHS gene in tomatoes was associated with
lack of fruiting, altered leaf morphology, higher rate of
photosynthesis and other changes.
Manipulated Organism:
Tomato (Lycopersicon esculentum mill.).
Inserted Transgenes:
Tomato gene DHS altered so that the gene would not be
correctly expressed. To achieve this it was inserted in an antisense
orientation. The antisense DHS gene was attached to the cauliflower
mosaic virus (CaMV-35S) promoter so that the target gene would be
expressed in all parts of the plant.
Goal:
Repress the expression of the enzyme DHS and examine the effects on
growth and development of the tomato plant. DHS catalyzes the conversion
of lysine to deoxyhypusine, an unusual amino acid. DHS is thought to be
present in all plant and animals cells, and is thought to be involved
generally in aging processes. In unmanipulated tomatoes it is expressed
in dying flowers, in softening fruit, and in prematurely dying leaves
of plants subjected to environmental stress. The overall aim of this
research is to investigate whether repressing DHS expression might be
a means to delay fruit ripening in tomatoes, which could make possible
longer transportation and storage times as well as increased shelf life.
Target Effect:
Nine plants (primary transformants) contained the transgenic antisense
DHS gene; of these, four produced fruit and from three of these,
transgenic tomato plant lines with suppressed DHS expression were
established and exhibited delayed fruit softening.
Nontarget Effects:
Five of the nine primary transformants that contained transgenic antisense
DHS did not produce fruits at all. One line was propagated
vegetatively; it had higher levels of DHS suppression than
the other three lines that formed fruit, and it exhibited significant
morphological and physiological side effects:
-
deformed pollen
-
no fruit unless cross-pollinated with wild-type pollen
-
larger and thicker leaves
-
more chlorophyll per unit surface area in the leaves
-
fewer internodes
-
in young leaves, 1.9 times higher photosynthesis activity than in wild
tomatoes, corresponding with increased starch deposition in the leaves
(up to 78% higher)
-
increased size of the stem pith
Additional Comments:
This research group carried out a similar experiment with the mustard
plant
Arabidopsis.
The highly contrasting results indicate how context-dependent gene
function is.
Source:
Wang, T., C. Zhang, W. Wu, L. Nowack et al. (2005). "Antisense
Suppression of Deoxyhypusine Synthase in Tomato Delays Fruit Softening
and Alters Growth and Development," Plant Physiology vol. 138,
pp. 1372-82.
Author Affiliations:
Department of Biology, University of Waterloo, Canada.
Funding:
Natural Sciences and Engineering Research Council of Canada.
Product Status:
Not on the market as of 2008.
Copyright 2008 The Nature
Institute.
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