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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.

Intended 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.

Unintended 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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