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Overexpression of phytoene synthase gene in Arabidopsis resulted in delayed germination, increased levels of chlorophyll, and changes in relative levels of carotenoids.

Manipulated Organism: Arabidopsis (Thale Cress; mustard family).

Inserted Transgenes: Multiple copies of the phytoene synthase gene from Arabidopsis, fused to the seed-specific napA promotor from oilseed rape to ensure that the genes are expressed in the seeds.

Goal: Increase the production of carotenoids in the seeds of Arabidopsis. The overall aim of this research is to engineer crops in a way that their seeds become a commercial resource for carotenoids. (See also: canola_001.)

Intended Effect: The transgenic Arabidopsis plants produced darker seeds, and extracts from the seeds showed a 43-fold average increase in the amount of beta-carotene. Significant amounts of lycopene and alpha-carotene were also found.

Unintended Effects:
  • The relative levels of the different carotenoids in the transgenic seeds were strikingly different from the composition in seeds of unaltered plants. For example, beta-carotene made up 28% of the carotenoids in transgenic seeds while in the seeds of controls only 4%; lutein made up 40% of carotenoids in the transgenic seeds and 61% in the seeds of controls.
  • In the seeds of transgenic plants several known and unknown carotenoids appeared that were not present in the seeds of the control plants.
  • The level of chlorophyll was increased, although the researchers had expected a decrease.
  • Seeds from the transgenic plants exhibited delayed germination. The carotenoid level was negatively correlated with germination.

Additional Comments: The authors remark: "Some of the results are in sharp contrast to results obtained from similar expression studies in canola. For example, overexpression of a bacterial phytoene synthase resulted in an equal increase of alpha- and beta-carotene amounts, whereas the levels of violaxanthin and lutein remained unaltered (Shewmaker et al. 1999). The increase of beta-carotene accumulation is similar to the result obtained in this study. . . . A clear difference in the accumulation of alpha-carotene was . . . found because the Arabidopsis plants did not produce relative levels of alpha-carotene as high as the canola seed. Even more intriguing is the difference between the levels of chlorophyll. In Arabidopsis, the levels of chlorophyll were significantly increased, and in canola the levels were decreased. We have no explanation for this difference" (p.783). To view the report on Shewmaker et al. 1999 click here.

Source: Lindgren, L. O., K. G. Stålberg, and A.-S. Höglund (2003). "Seed-Specific Overexpression of an Endogeneous Arabidopsis Phytoene Synthase Gene Results in Delayed Germination and Increased Levels of Carotenoids, Chlorophyll, and Abscisic Acid," Plant Physiology vol. 132, pp. 779-85.

Author Affiliations: Department of Plant Biology, Swedish University of Agricultural Science, Uppsala.

Funding: Stiftelsen för Lantbruksforskning, Ulla och Curt Nicolins Stipendiefond, and AstaCaroteneAB.

Product Status: Not on the market as of 2008.

Copyright 2008 The Nature Institute.

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